connecting rod & rod length too stroke info

[grumpyvette]

I build mostly BBC engines, but most of this info also applies to SBC connecting rod selection,
I was asked if stock rods were ok or should they swap to better ARP bolts or BUY the BETTER RODS WITH THE UPGRADED BOLTS,
the first thing Id point out is that, in most cases, when I diagnose engine failures , I see that its usually related to rod bolt stretch or valve train control issues or failures to check clearances, or occasionally failure to provide cooling or lubrication that are the major factors that cause problems, but by far, failure to check clearances , valve train stability issues at higher rpms and rod bolt stretch , and detonation issues are more common.
no connecting rod made can successful compress bent valves or loose chunks of detonation damaged piston, without damage occurring


http://www.wiseco.com/Calculators.aspx

failure to verify clearances, verify valve train geometry , provide lubrication, and maintain cooling , stay out of DETONATION,or use of inferior components or exceeding your engines valve train control limitations, or red line on rotating assembly design strength can get darn expensive
read these links

notice how the longer crank stroke effects the piston stroke distance in the bore, both at the lower and upper end of the cylinder
http://arp-bolts.com/pages/technical_failures.shtml

http://www.hotrod.com/techarticles/stee ... index.html

the 7/16" ARP connecting rod bolts are about 18% larger in cross sectional area than the 3/8" bolts and the better L19 or ARP 2000 bolts are a MINIMUM of 150% stronger than stock bolts even in the smaller 3/8" size,, the larger 7/16" is at least 200% stronger than the stock bolts in the rods., now rods can fail from high rpms and stress in other areas but its the rod bolts that fail in many cases, and in no case would I advise the use of stock 3/8" bolt connecting rods with lots of mileage on them be reused. the (H) design rods can be made slightly lighter in total weight for a given strength level, than a similar (I) beam rod, in the common 4340 steel forgings ,but tends to cost slightly more,(notice I DIDN,T SAY STRONGER, but STRONGER FOR A GIVEN WEIGHT) the weak point is usually the connecting rod bolts not the rod forging itself, always go with the 7/16" ARP bolts and the BOLT upgrade is advisable to L19 or better bolts once you start expecting to exceed 4000 feet per minute in piston speed, and its almost mandatory over 600hp and 4500 fpm (FEET PER MINUTE)in piston speed.
strength, obviously it depends on materials, design, care in manufacturing and which connecting rods are being compared properly prepared LS7 or L88 big block rods are a whole lot stronger than the stock 3/8" rod bolts big block rods, but many of the better aftermarket rods are significantly stronger that even the l88 rods
I beam rods typically have a balance pad and thats a good feature, typical H beam rods are SUPPOSED TO BE nearly identical in weight, as they are usually machined not castings (obviously they too occasionally need to be balanced)
theres not a thing wrong with either the (H) or (I) designs if the quality is there in the design and manufacturing.
for most high performance cars,the choice should probably be based on which design has better clearance too the cam lobes and block rails and the use of 7/16" arp bolts, and what kind of package deal you can get on an INTERNALLY BALANCE CRANK, DESIGNED FOR THE RODS if your looking to build the better assembly


look most stock chevy connecting rods are rated at no more than 6000rpm and 450-500hp
one factor to keep in mind is that rods typically have a side that rides against its matched companion and a side thats BEVELED for clearance on the crank journals radias EXAMPLE


notice how one side of the bearing holding section has a radias (left) but the opposite sides flush (right)


if you wonder why I suggest using SCAT (H) beam style cap screw connecting rods vs stock or most (I) beam designs this picture should show the increased cam to connecting rod clearance

notice the pin height in the pistons pictured above allow a longer or shorter connecting rod length


heres a selection of commonly available big block chevy connecting rod lengths
now I may be in the small minority here, but I have always given away 3/8" bolt sbc or bbc rods rather than use them and purchased the 7/16" versions or aftermarket 7/16" cap screw rods, WITH the L19 bolt upgrade,the 7/16" rods ARE significantly stronger. rod bolts are critical, high stress items and one of the areas most likely to cause problems at high rpms and loads.
cross sectional area of a 3/8" bolt is approx .11 sq inches, a 7/16" bolt is approx .15 sq inches BTW when you go to buy a ring compressor....this type works far better than the others




http://store.summitracing.com/partdetail.asp?autofilter=1&part=PRO%2D66766&N=700+115&autoview=sku

Proform 66766 $31


how they work is you clamp it around your piston and adjust it to that size before the rings are installed so the piston is a snug slide thru fit, then, install the rings, dip the rings and piston in clean oil, place the compressor over the cylinder on the block with the base firmly held against the block deck and push the piston into its much larger open entrance, as it slides thru the funnel like construction squeezes the rings into the grooves and they can,t spring back until they are in the bore, remember to line up the rod bolts and having them covered with the ends of a 3 ft long section or 3/8" fuel line to protect the crank journal is a good idea, having a ROD GUIDE TOOL you can use to guide and PULL THE PISTON INTO THE BORE WITH IS EVEN A BETTER IDEA
use those good L19 bolts and assuming you sellected the good L19 bolts that test at 220,000 psi, for each the differance is 24.2 thousand lbs vs 33 thousand lbs or a 36% increase in strength, but the stock rod bolts are 160,000 psi so your really swapping from about 17.6 thousand to 33 thousand in strength or an 88% stronger rod bolt


http://arp-bolts.com/pages/technical_torque_us.shtml

http://arp-bolts.com/pages/technical_installation.shtml

viewtopic.php?f=53&t=1168&p=12205&hilit=cleaning+rods#p12205

http://issuu.com/arpbolts/docs/catalog2 ... ipBtn=true

viewtopic.php?f=54&t=8463&p=29691&hilit=piston+squirters#p29691

reasonable quality connecting rods are CHEAP

http://www.cnc-motorsports.com/product.asp?ProdID=3150

http://www.cnc-motorsports.com/product.asp?ProdID=8817

viewtopic.php?f=86&t=10680&p=46162#p46162

keep in mind if a rod comes loose at high rpms you'll be LUCKY to save the intake, heads, blocks and cam are frequently damaged, spending an extra $90 for the better rod bolts is a total no brainer, in my opinion, if spending an extra $400-500 on rods and $90 on better bolts prevents rod failures, thats a minor consideration, when you may be spending $5500-$12,000 plus on an engine build.
you might also want to be aware that over revving and floating the valves, and using a poorly designed oil system is a major potential source of engine failures
I see rods and rod bolt failures blamed frequently when engines self destruct at high rpms, but its NOT always what it at first might appear to be....are there any detailed pictures of the rods or rod bolts that failed??? in many cases the source of the problem can be seen with a careful detailed exam, if you don,t know the SOURCE of the problem your doomed to repeat the sequence... [b]and keep in mind a good deal of what might appear to be rod/rod bolt failures, are ACTUALLY the result of over revving the valve train,and loss of valve train control, OR detonation, theres no way to compress a bent valve or broken piston ring land without potentially damaging the rods

well worth reading

http://www.rehermorrison.com/techtalk/63.htm

viewtopic.php?f=53&t=1168

viewtopic.php?f=53&t=1110&p=5644#p5644

http://arp-bolts.com/pages/technical_failures.shtml

IM OFTEN ASKED WHY I DON,T REBUILD CHEVY CONNECTING RODS, WELL MAYBE A PICTURE WILL HELP,

a good set of SCAT FORGED 4340 forged connecting rods costs less than $400 and they are 150%-200% stronger than MOST OEM chevy SBC rods
it will cost you almost that much to replace the bolts with ARP wave lock bolts, balance and polish and resize stock rods and you have far weaker rods when your done



Do not assume all the rod bolts will all take the same torque to get to the specified listed stretch

SUMMIT SELLS ROD BOLT STRETCH GAUGES
http://www.summitracing.com/parts/ARP-100-9942/

[grumpyvette]

http://victorylibrary.com/mopar/rod-tech-c.htm

http://www.stahlheaders.com/Lit_Rod%20Length.htm

http://emweb.unl.edu/Mechanics-Pages/Lu ... s%20VI.htm

http://rustpuppy.org/rodstudy.htm

http://www.iskycams.com/techtips.php#2005

viewtopic.php?f=53&t=247

http://drag.race-cars.com/techtips/tech ... 1047440910

http://www.grapeaperacing.com/GrapeApeR ... ngrods.pdf

http://www.hotrod.com/techarticles/stee ... index.html
more good info, BTW if your going to buy aftermarket connecting rods a stroker crank, higher compression pistons ETC,
BUY A COMPLETE BALANCED ROTATING ASSEMBLY FROM A SINGLE SOURCE

http://www.adperformance.com/index.php? ... x&cPath=71


http://www.ohiocrank.com/rotatepage1.html

http://www.dougherbert.com/enginecompon ... 1_611.html


when you go to clearance a block and select components read the fine print on what your buying and remember to clearance the block and rods to clear the cam lobes, a clearance of,0.050" is OK, Ive always suggested 0.060" but thats not enough difference in clearance in that application to worry about.
EXAMPLE SCAT,IF your looking to save money theres a good deal of variation in kit components,aftermarket connecting rods with ARP 3/8" bolts are significantly stronger than stock rod bolts, and connecting rods so they are a big improvement, but in the future Id suggest looking at similar 7/16" cap screw rod kits with internally balanced cranks for most builds as the cost is usually only minimally higher.
forged cranks are nice, to brag about, but certainly more expensive and not required for a street/strip 383 that seldom sees 6400rpm,or similar applications
as a general rule you'll find 7/16" rods add about 20% more strength for a minimal cost upgrade.

3/8" rods(Fastener Yield Strength (psi) 160,000 psi)
http://www.summitracing.com/parts/ESP-5700BPLW/


7/16" rods
Fastener Yield Strength (psi)200,000 psi

http://www.summitracing.com/parts/SCA-26000716/

http://www.summitracing.com/parts/SCA-25700716/

[grumpyvette]

I get asked all the time,
"should you re-use those stock rods, when I rebuild my 350 or when I build my 383 stroker"
most sbc gen I stock rods are designed to be cheap, and dependable in engines spinning under 6000rpm that make under 400hp,
this is one area where Im simply amused at the lack of thought shown in selecting components, by some guys.
most stock chevy small block rods are VASTLY inferior in strength to many of the mid range and better aftermarket rods available.
a 7/16" cap screw type ARP rod bolt is EASILY 200%-300% stronger than a stock 3/8" factory rod bolt and frankly, the cost & TIME to correctly modify and prep stock rods is a total waste, its almost always cheaper to buy decent aftermarket rods.

example

http://www.sdparts.com/product/12495071/5700quotPMConnectingRods.aspx
$265 for a set of stock rods and then you should still have ARP bolts installed, polish, balance and sized your looking at easily $500-$600 or more for a set ready to run

compared to something like this below its a joke

http://store.summitracing.com/partdetail.asp?part=SCA%2D6570021&autoview=sku

http://store.summitracing.com/partdetail.asp?part=SCA%2D25700716&autoview=sku


keep in mind theres far stronger rods available if you have some extra cash, and that connecting rods and their rod bolts are under a huge amount of stress at high rpms....one rod bolt stretching at high rpm will usually result in engine failure and its common for only the intake, valve covers, distributor, and water pump and a few other parts to be salvageable if that were to happen at high rpms...stretch a rod bolt and the piston contacts the head, or bends a valve, the rod bends, the heads destroyed, the block can be history and it can go down hill rapidly from there as fragments work their way around thru other of the moving parts as the engine locks up
ITS not generally HP but RPMS or lack of lubrication to the bearings that kills rods, I know guys with turbo cars that have carefully reworked stock rods pushing over 700 hp but they don,t generally exceed 6300rpm, rods generally fail in TENSION when the rod or rod bolts stretch /stretches not in compression due to cylinder pressure.
thats why the 7/16" rod bolts are so much better, as the bolts are the weakest component in most designs
on the compression stroke the whole rod structure resists deformation on the exhaust stroke the rod bolts are playing crack the whip and the rods trying to keep the piston from pulling/distorting it maybe 25-40 thousands it takes to prevent head to piston contact, and the bearing shells from distorting ,under the load so they don,t loose the oil pressure support, if the rod elongates and hits the head or valves in valve float bad things cascade into worse things fast.
the rod bolt cross sectional area is generally far smaller than the rod itself and if the piston compresses the rod a few thousands on the power stroke there not much effected, but let the rod stretch and bad things happen real fast.
a 7/16" rod bolt is about 20% larger in cross section than a 3/8" rod bolt and the L19 ARP steel in the better rod bolts is easily 50%-100% stronger than the stock rod bolt steel in many cases, giving a decent aftermarket cap screw rod design a significant strength advantage

[grumpyvette]

connecting rods and rod bolts are under a high stress, levels, if your going to buy cheaper non-brand name rods your taking a greater chance on having a part not meet minimal specs and strenght levels than the better brand rods and ARP rod bolts, but that doesn,t mean the rods are necessarly bad or not a good deal.
Ive used several OFF brand rods, in builds but I INSIST the guys supplying the parts for those builds use 4340 steel rods with 7/16" ARP rod bolts

SCAT , EAGLE and CAT parts have all proven to function
heres some sources I use

http://www.scatenterprises.com/

http://www.survivalmotorsports.com/

http://www.adperformance.com/

http://www.dougherbert.com/

[grumpyvette]

don,t get too concerned about your choice, between connecting rod lengths, here Ive built enought engines with both rod lengths to be sure both can result in a good combos

http://www.cnc-motorsports.com/product.asp?ProdID=8089

http://www.cnc-motorsports.com/product.asp?ProdID=8087

http://www.cnc-motorsports.com/product.asp?ProdID=3145&CtgID=1003

http://www.cnc-motorsports.com/product.asp?ProdID=6922&CtgID=1003

PROS/cons for 6"

KEEP IN MIND!!
the crank you select must have counter weights and clearances matching the rods you select, an INTERNALLY BALANCED CRANK IS UNDER LESS HIGH RPM STRESS
NEXT the ROD BOLTS you use in EITHER rod should be the ARP 7/16" CAP SCREW DESIGN as they are at least 150% -200% stronger than the stock 3/8" rod bolt and nut designs, and its the rod bolts stretching that cause many problems, BALANCING THE FULL ASSEMBLY IS CRITICAL TO LONG LIFE


Longer rod ratios have a longer dwell at TDC ,
In theory thats more high rpm tq for the 6" rods due to more efficient use of cylinder pressure at those high rpms but cam timing, scavenging and compression ratio must match to get the benefits, and detonation could be slightly more common
MATCHED ,CAM TIMING, PORT CROSS SECTION AND LENGTH< <COMPRESSION< AND EXHAUST HEADER CONSTRUCTION, DESIGNED TO MATCH THE LONGER ROD DWELL TIME IS REQUIRED TO ACCESS THE POTENTIAL BENEFITS, FAIL TO DO THAT CORRECTLY AND YOU LOOSE THE SLIGHT POTENTIAL GAINS
a 5.7" will have longer DWELL at BDC and move away from TDC slightly faster so in theory it can produce better low rpm tq and higher port vacuum readings but again,but cam timing, scavenging and compression ratio must match to get the benefits

less cylinder side wear/loading
lower angle reduces side thrust, and ring wear but the differance is something like two degrees of angle so its not super critical

lower over all piston/rod weight
longer rod allows a shorter piston that weights less and has more counter weight to skirt clearance between piston and crank, generally this makes for slightly less high rpm stress

HIGH PISTON PIN
the 6" rod places the upper edge of the piston pin hole in the lower oil ring, this is generally not a huge problem but more a P.I.T.A. due to extra precausions need to prevent the lower oil scraper from placing the ring gap in the unsupported areas

LOWER PISTON PIN
longer piston skirt, more stable piston in the bore and lower oil ring fully supported, but heavier piston and less clearance on crank counter weights

BOTTOM LINE
ITs generally a toss up as to which is better in a street application, I prefer the 6" but you will have fewer assembly problems with the 5.7" rods


HERES WHAT ISKY CAMS SAYS

"Rod Lengths/Ratios: Much ado about almost nothing.

Why do people change connecting rod lengths or alter their rod length to stroke ratios? I know why, they think they are changing them. They expect to gain (usually based upon the hype of some magazine article or the sales pitch of someone in the parts business) Torque or Horsepower here or there in rather significant "chunks". Well, they will experience some gains and losses here or there in torque and or H.P., but unfortunately these "chunks" everyone talks about are more like "chips".

To hear the hype about running a longer Rod and making more Torque @ low to mid RPM or mid to high RPM (yes, it is, believe it or not actually pitched both ways) you'd think that there must be a tremendous potential for gain, otherwise, why would anyone even bother? Good question. Let's begin with the basics. The manufacture's (Chevy, Ford, Chrysler etc.) employ automotive engineers and designers to do their best (especially today) in creating engine packages that are both powerful and efficient. They of course, must also consider longevity, for what good would come form designing an engine with say 5% more power at a price of one half the life factor? Obviously none. You usually don't get something for nothing - everything usually has its price. For example: I can design a cam with tremendous high RPM/H.P. potential, but it would be silly of me (not to mention the height of arrogance) to criticize the engineer who designed the stock camshaft. For this engine when I know how poorly this cam would perform at the lower operating RPM range in which this engineer was concerned with as his design objective!

Yet, I read of and hear about people who do this all the time with Rod lengths. They actually speak of the automotive engine designer responsible for running "such a short Rod" as a "stupid SOB." Well, folks I am here to tell you that those who spew such garbage should be ashamed of themselves - and not just because the original designer had different design criteria and objectives. I may shock some of you, but in your wildest dreams you are never going to achieve the level of power increase by changing your connecting rod lengths that you would, say in increasing compression ratio, cam duration or cylinder head flow capacity. To illustrate my point, take a look at the chart below. I have illustrated the crank angles and relative piston positions of today's most popular racing engine, the 3.48" stroke small block 350 V8 Chevy in standard 5.7", 6.00", 6.125" and 6.250" long rod lengths in 5 degree increments. Notice the infinitesimal (look it up in the dictionary) change in piston position for a given crank angle with the 4 different length rods. Not much here folks, but "oh, there must be a big difference in piston velocity, right?" Wrong! Again it's a marginal difference (check the source yourself - its performance calculator).

To hear all this hype about rod lengths I'm sure you were prepared for a nice 30, 40, or 50 HP increase, weren't you? Well its more like a 5-7 HP increase at best, and guess what? It comes at a price. The longer the rod, the closer your wrist pin boss will be to your ring lands. In extreme situations, 6.125" & 6.250" lengths for example, both ring and piston life are affected. The rings get a double whammy affect. First, with the pin boss crowding the rings, the normally designed space between the lands must be reduced to accommodate the higher wrist pin boss. Second, the rings wobble more and lose the seal of their fine edge as the piston rocks. A longer Rod influences the piston to dwell a bit longer at TDC than a shorter rod would and conversely, to dwell somewhat less at BDC. This is another area where people often get the information backwards.

In fact, this may surprise you, but I know of a gentleman who runs a 5.5" Rod in a 350 Small Block Chevy who makes more horsepower (we're talking top end here) than he would with a longer rod. Why? Because with a longer dwell time at BDC the short rod will actually allow you a slightly later intake closing point (about 1 or 2 degrees) in terms of crank angle, with the same piston rise in the cylinder. So in terms of the engines sensitivity to "reversion" with the shorter rod lengths you can run about 2-4 degrees more duration (1-2 degrees on both the opening & closing sides) without suffering this adverse affect! So much for the belief that longer rod's always enhance top end power!

Now to the subject of rod to stroke ratios. People are always looking for the "magic number" here - as if like Pythagoras they could possibly discover a mathematical relationship which would secure them a place in history. Rod to stroke ratios are for the most part the naturally occurring result of other engine design criteria. In other-words, much like with ignition timing (spark advance) they are what they are. In regards to the later, the actual number is not as important as finding the right point for a given engine. Why worry for example that a Chrysler "hemi" needs less spark advance that a Chevrolet "wedge" combustion chamber? The number in and of itself is not important and it is much the same with rod to stroke ratios. Unless you want to completely redesign the engine (including your block deck height etc.) leave your rod lengths alone. Let's not forget after all, most of us are not racing at the Indy 500 but rather are hot rodding stock blocks.

Only professional engine builders who have exhausted every other possible avenue of performance should ever consider a rod length change and even they should exercise care so as not to get caught up in the hype.





5.70" Verses 6.00" Rod Length Comparison Chart

http://www.iskycams.com/ART/techinfo/ncrank1.pdf


MORE INFO, and yes its worth your time to read thru it

http://www.stahlheaders.com/Lit_Rod%20Length.htm

http://victorylibrary.com/mopar/rod-tech-c.htm

http://em-ntserver.unl.edu/Mechanics-Pages/Luke-schreier/unzip/Tension%20and%20Compression%20in%20Connecting%20Rods%20VI.htm

http://www.grapeaperacing.com/tech/connectingrods.pdf

[grumpyvette]

I build mostly BBC engines but this also applies to SBC connecting rod sellection, I was asked if stock rods were ok or should they swap to better ARP bolts or BUY the BETTER RODS WITH THE UPGRADED BOLTS

look most stock chevy connecting rods are rated at no more than 6000rpm and 450-500hp

now I may be in the small minority here, but I have always given away 3/8" bolt sbc or bbc rods rather than use them and purchased the 7/16" versions or aftermarket 7/16" cap screw rods, WITH the L19 bolt upgrade,the 7/16" rods ARE significantly stronger. rod bolts are critical, high stress items and one of the areas most likely to cause problems at high rpms and loads.
cross sectional area of a 3/8" bolt is approx .11 sq inches, a 7/16" bolt is aprox .15 sq inchs
use those good L19 bolts and assuming you sellected the good L19 bolts that test at 220,000 psi, the differance is 24.2 thousand lbs vs 33 thousand lbs or a 36% increase in strength

http://arp-bolts.com/pages/technical_torque_us.shtml


reasonable quality connecting rods are CHEAP

http://www.cnc-motorsports.com/product.asp?ProdID=3150

http://www.cnc-motorsports.com/product.asp?ProdID=8817

keep in mind if a rod comes loose at high rpms youll be LUCKY to save the intake, heads, blocks and cam are frequently damaged, spending an extra $90 for the better rod bolts is a total no brainer, in my opinion, if spending an extra $400-500 on rods and $90 on better bolts prevents rod failures, thats a minor consideration, when you may be spending $5500-$12,000 plus on an engine build.
you might also want to be aware that over reving and floating the valves, and useing a poorly designed oil system is a major potential source of engine failures

I see rods and rod bolt failures blamed frequently when engines self destruct at high rpms, but its NOT always what it at first might appear to be....are there any detailed pictures of the rods or rod bolts that failed??? in many cases the source of the problem can be seen with a careful detailed exam, if you don,t know the SOURCE of the problem your doomed to repeat the sequence... [b]and keep in mind a good deal of what might appear to be rod/rodbolt failures, are ACTUALLY the result of over reving the valve train,and loss of valve train control, OR detonation, theres no way to compress a bent valve or broken piston ring land without potentially damaging the rods

read thru this

http://arp-bolts.com/pages/technical_failures.shtml

[grumpyvette]

no one ever said this hobby is cheap! think how foolish youll feel if a rod fails simply because you got cheap and tried to save $50-$100 at the cost of allowing your rods to be %50 weaker than spending $50-$100 more on your combo could have done.
lets look at it...
the first thing I do with 3/8" bolt big block rods is sell them,you can usually get ($50-$70 a set for them)
heres why
the 7/16" ARP connecting rod bolts are about 18% larger in cross sectional area than the 3/8" bolts and the better L19 or ARP 2000 bolts are a MINIMUM of 150% stronger than stock bolts even in the smaller 3/8" size,, the larger 7/16" is at least 200% stronger than the stock bolts in the rods.
but ID strongly resist the urge to just drill out and install 7/16" ARP rod bolts in rods designed for the 3/8" rod bolts, theres a very good chance youll have removed enought material from around the bolt to effect its strength.
the amazing thing is that the total out the door cost of even the moderate aftermarket forged 4340 cap screw rods, is similar or even cheaper than the ,machine shop cost of the arp bolts and reworking the stock connecting rods.
BTW THE $90 ROD BOLT UPGRADE IS WELL WORTH IT IF YOUR PUSHING THE UPPER RPM LIMITS IN YOUR ENGINE BUILD

http://www.adperformance.com/index.php? ... cts_id=519

http://www.adperformance.com/index.php? ... cts_id=243



your average machine shop charges at least $120 to add the bolts and resize the rods, the bolts themselfs cost about $80, so your into those rods for about $200 minimum,now if your smart youll also have them magnaflux checked for stress cracks (another $50 minimum)now that $$200-$250 machine shop cost plus the $50-$70 minimum youll normally make selling the stock rods goes a LONG WAY toward upgradeing) yet a 3/8" rod bolt is a MINIMUM of 7000psi weaker than a 7/16 rod bolt due to the differance in cross section, now add to that the fact that the (H) style rods are rated at LEAST 50% stronger,are usually lighter in weight and closer in tollerance and require less ballancing and youll quickly find that the work necessary to get those 3/8" rods up to racing condition is wasted time and money in a true high performance engine

http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=1397&prmenbr=361

lets see, recondition old 3/8" rods = hours of work and costs $250-$300 minimum and they are still 50% weaker
OR
buy new (H) style cap screw 7/16" rods that are 50% stronger that require HOURS less work, are closer tollerance and cost on average $350-$400 NEW [color:"black"]remember that $400 is really minus the $250-$300 youll spend on the old rods so its only $50-$100 more for the up-grade [/color] plus they have more cam to rod bolt clearance in the block and require less grinding on the pan rails if a stroker cranks used, and if your buying pistons also you can buy a longer rod at minimal cost to improve the engines rod/stroke ratio!

http://www.flatlanderracing.com/crhbeamscat.htmlIF you already have 3/8" bolt big block rods and are about to rebuild the big block engine, please understand IM CERTAINLY NOT trying to rain on your parade! what I am trying to do is show anyone reading the thread, that the stock 3/8" rods are not the best choice to spend your money on and that proper planing helps the over all combos strength for the money spent
IVE seen to many guys spend major amounts of money
pollishing
shot peaning
resizing
ballancing
and ,magnafluxing stock rods
and winding up spending more and having less with stock rods then they might have had for the same or less money with aftermarket FORGED 7/16" bolt rods with careful shopping. you will occasionally get great deals on those rods on EBAY or at the LOCAL speed shops

[grumpyvette]

GOSFAST posted this great photo to illustrate the differance between rod designs



http://www.scatcrankshafts.com/index.htm

rods designed like the 3 SERIES generally won,t work with stroker cranks while the 2 series usually will

the connecting rods you sellect make a huge differance in the rod to cam lobe clearance, even a small base cam won,t clear some designs, it should be obvious that the connecting rod with the thru bolt has a great deal less cam lobe clearance potentially than the cap screw design next to it., and the cap screw rod probably clears the blocks oil pan rail area easier also

Im running that crane 119661 cam retarded 4 degrees BTW but detonation has not been a problem, remember that the coolant temp, air temps the engine sees, QUENCH distance, type of head gasket and its construction ,ignition advance,plug heat range,piston to bore clearance, exhaust valve seat width, and oil temp and pollishing your combustion chamber and piston domes, and your AIR/FUEL RATIO , and the effective DYNAMIC compression ratio, have a noticable effect on detonation


and if you do see detonation, theres octane boosters like TOULUENE

http://www.gnttype.org/techarea/misc/octanebooster.html

http://www.team.net/sol/tech/octane_b.html

http://www.elektro.com/~audi/audi/toluene.html

READ THIS

http://www.rehermorrison.com/techtalk/02.htm

many guys don,t realize that the rod bolt material and cross sectional area are critical to durrability , especially in a high rpm range combo,while the rods themselfs ocassionally fail, its much more likely that the rod bolts lost thier clamping strength, stretched a bit first and that was a major contributing factor in the bearing failure or the rod failure process.



interesting info from ARP





Other Stresses

It must be realized that the direct reciprocating load is not the only source of stresses in bolts. A secondary effect arises because of the flexibility of the journal end of the connecting rod. The reciprocating load causes bending deformation of the bolted joint (yes, even steel deforms under load). This deformation causes bending stresses in the bolt as well as in the rod itself. These bending stresses fluctuate from zero to their maximum level during each revolution of the crankshaft.

Fastener Load

The first step in the process of designing a connecting rod bolt is to determine the load that it must carry. This is accomplished by calculating the dynamic force caused by the oscillating piston and connecting rod. This force is determined from the classical concept that force equals mass times acceleration. The mass includes the mass of the piston plus a portion of the mass of the rod. This mass undergoes oscillating motion as the crankshaft rotates. The resulting acceleration, which is at its maximum value when the piston is at top dead center and bottom dead center, is proportional to the stroke and the square of the engine speed. The oscillating force is sometimes called the reciprocating weight. Its numerical value is proportional to:
It is seen that the design load, the reciprocating weight, depends on the square of the RPM speed. This means that if the speed is doubled, for example, the design load is increased by a factor of 4. This relationship is shown graphically below for one particular rod and piston


http://www.arp-bolts.com/Tech/TechWhy.html


I did a quick DOUBLE TAKE on that bottom graph the first time also....look closer at the edges of the graph, its points out the STRONGER the material USED the SMALLER the dia. necessary for a given tensile strength, your limited in clearance on rod bolt max size so the material needs to have higher yeild strength, and potential durrability, to increase the rod bolt strength

FROM ARP

"Metallurgy for the Non-Engineer

By Russell Sherman, PE

1. What is grain size and how important is it?

Metals freeze from the liquid state during melting from many origins (called allotropic) and each one of these origins grows until it bumps into another during freezing. Each of these is a grain and in castings, they are fairly large. Grains can be refined (made smaller); therefore, many more of them can occupy the same space, by first cold working and then by recrystallizing at high temperature. Alloy steels, like chrome moly, do not need any cold work; to do this – reheat treatment will refine the grain size. But austenitic steels and aluminum require cold work first. Grain size is very important for mechanical properties. High temperature creep properties are enhanced by large grains but good toughness and fatigue require fine grain size-the finer the better. (High temp creep occurs at elevated temperature and depending on material and load could be as much as .001 per inch/per hour.) All ARP bolts and studs are fine grain – usually ASTM 8 or finer. With 10 being the finest.

2. How do you get toughness vs. brittleness?

With steels, as the strength goes up, the toughness decreases. At too high a strength, the metal tends to be brittle. And threads accentuate the brittleness. A tool steel which can be heat-treated to 350,000 psi, would be a disaster as a bolt because of the threads."

http://www.arp-bolts.com/Tech/TechMetals.html

[grumpyvette]

theres a wide sellection of connecting rods you can choose from,and even some of the less expensive 4340 steel rods with ARP 7/16" rod bolts make a decent component for a street strip engine up to easily 600hp, , but its very hard to tell just looking, because the type of steel,critical measurements, heat treating and pollishing are hard to identify by looks,alone,IVE used alot of SCAT,AND CROWER rods and a few LUNATI and MANLEY and all the 4340 STEEL RODS with 7/16" ARP bolts have worked just fine.
I would strongly suggest a KNOWN NAME brand and insist on ARP bolts
NEVER SCRIMP ON RODS, ROD BOLTS, BEARINGS OR VALVE SPRINGS
more connecting rod info

http://www.nolimitmotorsport.com/eagle/

http://emweb.unl.edu/Mechanics-Pages/Lu ... s%20VI.htm

[grumpyvette]

http://store.summitracing.com/partdetai ... toview=sku


http://store.summitracing.com/partdetai ... toview=sku

heres a stretch chart
http://www.arp-bolts.com/Tech/TechTorque.html


Do not assume all the rod bolts will all take the same torque to get to the specified listed stretch

SUMMIT SELLS ROD BOLT STRETCH GAUGES
http://www.summitracing.com/parts/ARP-100-9942/


heres the short version,AFTER each rods installed with its bearing on the crank, durring the short block assembly process,set the stretch gauge to zero on the bolts unstretched length, you use a torque wrench on rod bolts lubed with assembly lube too tighten each of them in several stages, tighten the rod bolts to the recomended torque then loosen them and re-tighten them a minimum of three times each, after the final torque value is reached for the third time, you check each bolt against the chart values, most will be a bit short,of the full permited stretch value, while the bolts being meassured , you can slip the stretch gauge off for a second and use the correct long wrench to further tighten them slowly and carefully too just under or up too the stretch chart limits in length, if they are not at that length due to the torque wrench stretching the bolt,this insures max clamping loads, without exceeding the bolts elastic limits so its at max holding strength for the application. cycling the bolt thru several cycles tends to make sure its firmly seated and fully stretched and tends to find problems like deffective bolts, and bolt that doesn,t shrink back below the chart value when the tensions released is deffective and needs replacement




FROM ARP

"We highly recommend using a stretch gauge when installing rod bolts and other fasteners where it is possible to measure the length of the fastener. It is the most accurate way to determine the correct pre-load in the rod bolt.

Simply follow manufacturer’s instructions, or use the chart on page 25 of the ARP catalog for ARP fasteners.

Measure the fastener prior to starting, and monitor overall length during installation. When the bolt has stretched the specified amount, the correct preload, or clamping load, has been applied.

We recommend you maintain a chart of all rod bolts, and copy down the length of the fastener prior to and after installation. If there is a permanent increase of .001˝ in length, or if there is deformation, the bolt should be replaced. "

http://www.carcraft.com/techarticles/11 ... index.html


a few more less expensive tools

http://www.chevyhiperformance.com/techa ... rices.html

[grumpyvette]

in the constant quest for increased performance many guys install stroker cranks to gain displacement, many guys don,t consider the changes in stroke mandate other changes such as increased friction from the changed rod angles and clearance issues plus the reduction in peak rpms that the increased piston speeds the longer strokes mandate will require.
longer strokes tend to have increased rotational friction and lower rod length to stroke ratios
both tend to limit upper rpm cylinder filling efficiency, longer strokes are not necessarily, a bad thing as the increased displacement helps torque but your valve size needs to keep pace with the displacement, and in many cases the restriction in max valve size, and the related curtain or flow potential, that the engines bore limits you too, will cause major increases in stroke to only produce slightly more torque
the IDEAL bore to stroke ratio and rod length, (from seeing the results of many engine dynos) seem to fall close to a range of stroke should be between about .70-.75 of bore diam.and rod length should be between about 1.55-1.9 times the stroke, but theres been many successful combos that did not fall into that basic range
examples of very efficient engines that maximize the horsepower per cubic inch of their displacement
are the 302 Chevy with its 3" stroke and 4" bore and the 477 BIG BLOCK with its 4.5" bore and 3.76" stroke
neither is ideal but both engine combos tend to produce excellent power for their displacement when the correct components are used to build them, but Id also point out that the common strokes on the same bore (the 383 in the 302s case and the 540bbc in the 477s case)produce MORE TORQUE AND HORSEPOWER, just not as much horse power PER CUBIC INCH OF DISPLACEMENT
in an ideal world having a 1.9:1 rod/stroke is great, in theory its worth a few extra hp and reduces friction and thrust drag on the cylinder walls, in the real world as long as your crank counter weights clear the piston skirts at bdc by at least .060 and the pistons don,t get closer than about .037 to the heads at TDC the rod length is not super critical as long as the piston speed stays under about 4000 fpm (feet per minute)with components similar to stock and with forged balanced components 4500fpm may be tolerated for brief periods...youll seldom have problems unless the valve train or lube system fails

QUOTE
"Under-square engines

These produce strong torque at low to mid range rpm's because of the "leverage" advantage of a longer stroke. But, under-square can be a negative trait, since a longer stroke usually means greater friction, a weaker crankshaft and a smaller bore means smaller valves which restricts gaseous exchange; however, modern technology has lessened these problems (explanation?). An under-square engine usually has a lower redline, but should generate more low-end torque. In addition, a longer stroke engine can have a higher compression ratio with the same octane fuel compared to a similar displacement engine with a much shorter stroke ratio. This also equals better fuel economy and somewhat better emissions. Going undersquare can cause pistons to wear more quickly (greater side-loads on the cylinder walls) and can cause ring seal problems and lubrication problems; with increased loads on the crankshaft, pistons, the piston pins, connecting rods, and rod bearings (due to piston speed). In general, a longer stroke leads to higher thermal efficiency through faster burning and lower overall chamber heat loss. A longer stroke will have greater port velocity at a given RPM, more torque due to more leverage on the crank, will achieve it's greatest efficiency at a lower RPM. Smaller combustion chambers are also more efficient, with the flame front having a shorter distance to travel- this leads to being more detonation resistant, and having an advantage for emissions.


Over-square engines

These are generally more reliable, wears less, and can be run at a higher speed. In over-square engines power does not suffer, but low-end torque does - it being relative to crank throw (distance from the crank center to the crank-pin). An over-square engine cannot have as high a compression ratio as a similar engine with a much higher stroke ratio, and using the same octane fuel. This causes the over-square engine to have poorer fuel economy, and somewhat poorer exhaust emissions. Breathing is an important advantage for over-square engines, as the edges of the valves are less obstructed by the cylinder wall (called "un-shrouded"). The big bore can fit larger (or more) valves into the head and give them more breathing room.

With shorter crankshaft stroke (and therefore piston travel) parasitic losses are reduced. Ring drag is the major source of internal friction and the crankshaft assembly also rotates in a smaller arc, so the windage is reduced. Oil-pressure problems caused by windage and oil aeration are lessened."

you might want to read thru these links

http://www.strokerengine.com/RodStroke.html

http://www.wallaceracing.com/enginetheory.htm

viewtopic.php?f=53&t=343&p=6341&hilit=redline#p6341

http://www.purplesagetradingpost.com/su ... ngine.html

viewtopic.php?f=53&t=510

http://www.rbracing-rsr.com/runnertorquecalc.html

http://hemrickperformance.com/valve.aspx

http://www.rustpuppy.org/rodstudy.htm

http://www.wallaceracing.com/runnertorquecalc.php

http://www.swartzracingmanifolds.com/tech/index.htm

http://tomorrowstechnician.com/Article/ ... adder.aspx

http://victorylibrary.com/mopar/intake-tech-c.htm

viewtopic.php?f=53&t=343&p=6341&hilit=redline#p6341

http://victorylibrary.com/mopar/chamber-tech-c.htm

http://victorylibrary.com/mopar/cam-tech-c.htm

http://victorylibrary.com/mopar/rod-tech-c.htm

http://victorylibrary.com/mopar/piston_position-c.htm

viewtopic.php?f=52&t=1070

[grumpyvette]

Connecting Rods - Enginology
On The Rod Again...
From the November, 2010 issue of Circle Track
By Jim McFarland

http://www.circletrack.com/enginetech/c ... ength.html

Connecting Rods
Connecting rod geometry, particularly...



read full caption
Connecting Rods
Connecting rod geometry, particularly center-to-center length, can have a material influence on a variety of engine conditions.
It is generally acknowledged that connecting rod geometry, particularly center-to-center length, can have a material influence on a variety of engine conditions. These include specific relationships to valve timing (camshaft design), cylinder pressure history, spark ignition timing requirements and torque output, the latter with respect to the actual shape of torque curves. We'll touch on the more important of these a bit later.

Depending upon specific applications, connecting rods are perhaps some of the most highly stressed parts in an engine, particularly those intended for racing. From the high loads experienced at and just beyond TDC piston position during combustion to the tensile and unsymmetrical loading caused by offset piston pin axis, loads that are actually opposite to combustion pressure loads and stresses set up by lateral inertia, connecting rods become virtual "whips" that mechanically join pistons to the crankshaft.

Further complicating the issue are vibratory loads caused by oscillatory motion of a crankshaft, rotating about its axis while spinning in a normal direction. Visualize this set of load conditions in very slow motion. Each firing impulse intended to accelerate crankshaft rotation is applied as a force delivered in a span of time. Because of its inertia, a crankshaft can't immediately increase its speed and, therefore, is momentarily deflected in the same direction as its rotation. This deflection is local to the crank pin to which the load-delivering connecting rod is attached. Then, because of its elasticity, the crankshaft (at that pin location) will spring back against its direction of rotation, continuing this back-and-forth oscillatory motion until the next firing pulse is delivered to that particular crank pin. The connecting rod is thereby required to absorb what amounts to a series of tensile and compressive loads caused by oscillations of the crank pin, during primary crankshaft rotation.

Keep in mind that we've just provided a very simplistic description of the load dynamics experienced by the connecting rod for only one operational cylinder. The complexity of this varying load environment is increased by orders of magnitude when you add another seven cylinders and turn up the wick on rpm. So, when you think about connecting rods as "shock absorbers," several issues come to mind.

For example, consider cylinder pressure loads not as "hammer blows" to a piston but very rapid pressure rises that are influenced by combustion flame rate and net combustion pressure development. We also know that this pressure "history" is not constant or uniform as it is applied to a piston. Plus, whatever auxiliary forces are applied to a piston are also transferred in some way into the connecting rod. Rods can be designed too stiff, thereby transferring combustion pressure too aggressively to rod bearings and crank journal bearings. They can also be too flexible, and neither condition is acceptable. But in any case, rods need to absorb load spikes and minimize pressure transfer loss to prevent a waste of torque that's ultimately produced by the crank.

Perhaps one area of concern where connecting rod stiffness is important deals with vibratory loads produced by the torsional stiffness of a connecting rod's beam section, as piston weight is reduced. As you might expect, the reduction of rotating and reciprocating mass in an engine's crankshaft assembly can become a trade-off to the absorption of gas and mechanical loads by sheer mass alone. Visualize throwing a medicine ball to a 150-pound person and then to a 250-pounder and you may understand this more clearly.

Of course, to minimize the rotational resistance of a crankshaft assembly, reducing the weight of pistons and rods is a time-honored approach. However, compromising weight for strength and durability is the fulcrum about which this issue pivots. Perhaps one exception to this "rule" was in the early design of composite connecting rods (the so-called "poly motor" of years past), in which first-design rods were inordinately stiff and caused rod bearing failures for a lack of load absorption capability. On the other hand, lightweight materials that offer strength and low mass may be too costly to market, even in the average racing engine. So while other considerations must be included, the fundamental objectives should include strength, low weight, and durability.

In speaking with leading connecting rod manufacturers, you often hear that a high percentage of rod failures don't occur during the high pressure of combustion. Rather, it's during the exhaust stroke that a rod gets "yanked" away from TDC. This sudden movement of the piston causes abnormally high tensile loads in the rod's beam and leads to a fracture in this area, typically somewhere just below the piston pin end.

Also, failures can occur during either valve float or conditions of over-revving the engine. What happens is that the open valves (and lost combustion pressure) don't provide any sort of a cushion for pistons heading toward TDC. So when they pass through TDC, there's nothing to stop them from being "pitched" at the cylinder heads, often leading to another cause of tensile fracture in the beam section. In fact, the "effective" or dynamic weight of a piston passing through TDC under these conditions can be far in excess of its actual static weight. Multiple times, in fact.

Connecting Rods - Enginology

Connecting Rods
Connecting rods become virtual...

read full caption
Connecting Rods
Connecting rods become virtual "whips" that mechanically join pistons to the crankshaft and sometimes they fail. But situations like the one pictured above can be avoided by properly selecting and integrating various internal engine components.
Yet another common location for rod failure is a portion sometimes called the "hinge point," which is generally where a connecting rod's beam section changes in cross-section area (wide to narrow). Connecting rod designers frequently work in this area to determine the best compromises between rod strength and material selection. Of course, you should always include proper rod side-clearance, making certain not to provide excessive dimension that allows oil to create over-oiling of cylinder walls. Insufficient side-clearance can lead to over-heated and failed rod bearings, as well.

Finally, if we assume that a piston represents the "floor" of an engine's combustion space, then the rate of piston movement and time spent at each crankshaft angle will affect the rate of change in combustion space (volume). Of the reasons this is important, one is that piston movement can affect mixture density during the compression stroke (and subsequent flame rate and rise of combustion pressure). This, in turn, bears influence on spark ignition timing and the optimization of IMEP (minimizing "negative" torque). During an exhaust cycle, piston motion can also affect efficient cylinder evacuation and, therefore, is linked to proper exhaust valve timing.

Just considering these two peripherals of piston movement, we can immediately see that any changes to a piston's rate of travel may affect net cylinder pressure and power. Connecting rod length can, and does, influence cylinder pressure. Perhaps obscure is the fact that while longer connecting rods produce a larger included angle between rod axis and crank throw (stroke) at the same piston position and crank angle, it is piston motion approaching and leaving TDC and BDC that provides some interesting study.

Here's an example of that. As connecting rod length is increased, piston motion (both acceleration and velocity) away from TDC decreases. This results in a slower rate of pressure drop across the inlet path, therefore causing a reduction in intake flow rate (all else being equal). Unless compensation is made for this change in piston speed, some degree of volumetric efficiency may be lost.

In contrast to this effect upon volumetric efficiency (potential torque), piston "residence time" at and near TDC during combustion tends to hasten flame rate, correspondingly raise cylinder pressure per unit time, and enhance the tendency toward detonation. Reduced initial (or total) ignition spark timing, applied to reduce pre-TDC cylinder pressure, also increases IMEP by the reduction of negative torque. Or it can work against the piston as it approaches TDC during combustion.

Long rod combinations usually like intake manifold passages (actually heads and manifold) that help boost flow rates not provided by more rapidly descending pistons associated with shorter rods. So in addition to adjusting valve timing and lift patterns to match changes in piston speed needed to increase volumetric efficiency for increased rod length, port section areas and even carburetor sizing can be used to help restore reduced flow rates.

There is also the issue with reduced piston side-loading with long rod use. This reduction in friction horsepower has been attributed to power gains, especially when piston speed increases beyond about 2,500 feet/second. Improved ring life with long rods has also been claimed by some engine builders.

So while none of this month's Enginology was intended to advocate the use of short or long connecting rods, it emphasizes the importance of contemplating other engine functions that required consideration when making material changes to the rate of piston travel as a direct function of crankshaft angle. You will find that knowledgeable parts manufacturers, relative to the subject of connecting rod length, generally have a store of information linking how their components can affect an engine's ability to capitalize on rod length changes. If they don't, you may want to consider finding manufacturers who do. The concept of functional parts integration isn't without basis.

[enigma57]

Thanks, Grumpy! As it happens, I am right in the middle of a long stroke small block build and I will certainly read over all the links you posted before proceeding.

Best regards,

Harry

[grumpyvette]

Figuring Compression Height of a piston

The compression height is the distance from the center of the wrist pin hole to the top deck of the piston. (see attached pix)

Custom pistons are available in any practical compression height to compensate for stroker or de-stroker cranks, long rods, or blocks which have been milled excessively, etc. Winston Cup & Busch motors usually have a very low or small compression height. (1.245 to 1.12 inches) The reason is that they have a shorter than stock stroke with a longer than stock rod length.
Ive always preferred to keep the piston pin out of the lower oil ring groove if I can, a compression height in the 1.5-1.375 range or larger will frequently allow that , but obviously each piston supplier will have a slightly different design, and obviously the applications will differ so you may be required to select something thats not always your ideal compromise
keep in mind theres some leeway, in that head gaskets can be used with different thicknesses to maintain a set quench distance, so if a piston sticks lets say as an example .010 out of the bore a .050 thick head gasket could be selected to maintain a .040 quench, if the pistons .015 down the bore, a thinner .025 head gasket could be used, so if your calculations show you need a 1.4" compression height a 1.390-1.410 could be used in most cases giving you a bit more choice selecting pistons

1st thing you need to know is the block height. To find this you need to measure from the crankshaft center line to the deck (cylinder head mounting surface) of the block.



2nd Next thing is rod length. To determine exact rod length, you should have a good pair of calipers to measure with. Measure the size of the rod bearing opening (big hole) and the size of the wrist pin opening, and divide them in two (or one half) Finally, determine the distance between the two openings (center of the rod) and add the half you just calculated. That gives you the rod length. It comes out to be the distance between the center of the two holes.

Finally you need the stroke length.









Stroke length is;

twice the distance from the center line of the crankshaft main bearing journals to the cente rline of the connecting rod journals or ;

It is also the distance the piston moves up and down in the cylinder



Now that you have all the info, you can calculate the compression height of the piston;



To calculate the compression height, use the following formula:

Block Height minus 1/2 the crank stroke, minus the rod length, minus the deck clearance (amount piston is "in the hole").

For example, a 350 Chevy engine with a stock 3.480 stroke, stock length 5.700 rod, standard .017 deck clearance and standard 9.025 block height would be:

3.480 stroke divided by 2 = 1.740

9.025 - 1.740 - 5.700 - .017 = a compression height of 1.568.

if you were building a 496 BBC the deck height on the standard blocks 9.8"
rods are typically 6.385"
stroke is 4.25", so half the stroke is 2.125" plus 6.385" rod length, subtracted from 9.8" deck height, =1.29" piston compression height

https://www.uempistons.com/index.php?ma ... iston_comp

related info

viewtopic.php?f=52&t=4081&p=12278&hilit=quench#p12278

viewtopic.php?f=52&t=727

http://www.kb-silvolite.com/calc.php?action=piston_comp

viewtopic.php?f=53&t=3061&p=8095&hilit=piston+suppliers#p8095

viewtopic.php?f=53&t=2208&p=5942&hilit=piston+suppliers#p5942

viewtopic.php?f=69&t=2645&p=6834#p6834

http://www.lunatipower.com/Tech/Pistons ... eight.aspx

[enigma57]

Great info, Grumpy! The diagrams make it much easier to visualize the relationship of the various component parts that make up an engine and how they work together.

Thanks,

Harry

[grumpyvette]

quote=enigma57

"If I replaced the entire reciprocating assembly with a crank having 1/8" less stroke and went to longer 6" rods and pistons having a comp. height of 1.0875", it would improve rod/stroke ratio somewhat.....

4.000" stroke / 5.850" rod = 1.462:1 (My present combo)
3.875" stroke / 6.000" rod = 1.548:1 (New combo)
3.75" stroke / 6.000" rod= 1.6:1


Or I could destroke to 3.300" and use 6.2" rods along with my present 4.125" bore pistons having 1.170" comp. height......

3.300" stroke / 6.200" rod = 1.878:1 (This combo should rev easily and nets 352.8 cu. in. displacement)
3.000" stroke / 5.700" rod = 1.900:1 (stock 265,283,302)"


ok lets say youve got a new dart block with a 4.125" bore and your selecting a crank, youve narrowed the choices to a 3.30", a 3.75" and a 4" stroke crank combo


I think your placing a bit more concern on rod to stroke ratio and rod angle than is warranted, under the conditions.
every choice has a compromise in some area, and as the rpms go up so does the stress on the rotating components and valve train.

keep in mind that your likely to produce about 1.25-1.35 hp per cubic inch with a well tuned combo like you've described , lets assume the larger combo only makes 1.25 hp per cubic inch and a de-stroker with its better rod angle makes a full 1.35:1 cubic inch

427 x 1.25=534(4" stroke)
372 x 1.35=502 (3.75" stroke)
352 x 1.35=476 (3.30 stroke)
but keep in mind the larger engines going to have about a 30-60 ft lb or more torque advantage over the smaller displacement combos over most of the rpm range and that power will come in at about 400rpm-600rpm lower and its responsive low and mid rpm torque that tends to be far more important than peak hp on a street car.
and its going to be cheaper and easier to maintain valve train control,at 6300rpm and below a good hydraulic roller cam,possibly with a rev kit should control the valve train,
yes there's some advantage in the better rod stroke ratio, but it will quickly be compromised by the need to rev the engine to higher rpms and valve train control issues , in many combo, less say your limiting the engine to 4200fpm in piston speed?
a 4" stroke=6300rpm . or about the max rpm any hydraulic lifter valve train is likely to function reliably
a 3.75" stroke=6700rpm =surely solid lifter rpm with a stud girdle
a 3.5" stroke=7200rpm=surely solid lifter rpm =shaft rocker time
a 3.3" stroke=7600rpm=surely solid lifter rpm =shaft rocker time
I get asked why the 301/302-327-331 sbc engine, is just not seen as commonly any more, the basic reason is the 283-327 they were built from is no longer as common as the current 350 basic core engine the 383-396-401 gets built from, as the 350 sbc is far more common.
just some info guys....there's a GOOD REASON why the 302 is less than popular compared to a 383-401 stroker built from a 350 basic block.
THERE'S NO way a 302 with its 3" stroke and the higher stress on the valve train that rpms over 7000rpm that the 302 sees will match the results and dependability a 383-396-401 stroker combo with its 3.75"-3.875" stroke and under 6500rpm valve train stress will produce
lets say a 302 can produce 1.25-1.4 hp per cubic inch, you can do the same with a 396 sbc
your looking at say 410 hp for the 302 and a similar 396 sbc costing almost the same will produce 535 hp with the same hp per cubic inch WITH LOWER VALVE TRAIN STRESS, its a FACT your far more likely to have valve train problems at over 6500rpm than under that rpm
there's also a much faster ramp up on the torque curve with the larger displacement.
we USED to build 301-327-331 sbc when the cylinder heads flow limited the effective displacement that could effectively be fed, those days are long gone, with the current aftermarket heads.

example

http://airflowresearch.com/articles/article031/A-P1.htm

http://www.chevytalk.org/fusionbb/showt ... id/131229/

http://www.bracketmasters.com/small_blo ... 383_cu.htm

http://airflowresearch.com/articles/art ... A14-P1.htm

http://airflowresearch.com/articles/art ... A16-P1.htm

BTW USING A HYDRAULIC LIFTER VALVE TRAIN in a 302-331 SBC that's built for MAX HP,is about as useful as snow shoes on a snake

ID also point out the differences in bearing sizes and the difficulty in building good compression with flat top pistons with the shorter stroke combos



for those guys that think high rpms are the way too go....,think about this, in a correctly clearanced and balanced lower assembly,
piston speeds should almost always be UNDER 4000fpm with correctly reworked stock type parts , or 4500FPM with all forged aftermarket race quality parts, if you expect the lower assembly to live a decent life span, that's,
between 8000-9000rpm on a 302 and 6400-7200 rpm with a 383 so as you should see, its far more likely the valve train is the weak link that determines the RED LINE
since the cars engine speed is usually restricted to the rate of acceleration of the car due too the engine being locked into driving the drive train,the larger engine has a slight advantage in acceleration with equal rear gears but in the real world you'll run 3.73:1-4.33:1 rear gears with a 383 and 4.56:1-5.13:1 with a 302, making the crank acceleration rates similar, or higher with the 302.
personally Ive never seen any advantage to spinning a smaller stroke engine to higher rpms, to make power, the stress on the valve train and lower assembly tends to cause more parts failures, its a whole lot easier to control valves at 6000rpm than at 8000rpm, and it gets darn expensive when pistons kiss valves, keep the engine operating well within its safe/ low stress speed,limits and it will last far longer.
at 8000rpm the valves open and close in each cylinder 67 TIMES A SECOND, your approaching absurd inertial loads and control problems well under that at 6400 rpm where the valves open and close at 53 times a second






[/color]
the discussion about whats the best connecting rod length to stroke ratio and what rod design should be selected has been hashed thru in a near endless debate, I,d suggest you pay a great deal of attention to the quality of the connecting rods, bearings used, quench,clearances and engine lubrication, and preventing detonation, and maximize oil and coolant cooling to keep both in a reasonable range (THERE THREADS ABOUT THIS) and use an internally balanced rotating assembly, and while longer rod ratios are in theory beneficial the proven benefits are usually minimal as long as you keep the piston speeds reasonable
before I even begin,to discuss this Id strongly suggest IF your planing an engine build, that you purchase a complete matched rotating assembly, thats internally balanced from a well known manufacturer, and an SFI certified DAMPER AND FLYWHEEL OR FLEX-PLATE because any attempt at matching, miss matched components will result in zero warranty on any problem, fitting, matching or breaking in,the components

anyone who understands physics and geometry and can use a calculator or do minimal research into those questions,understands that a change in rod length will also change several other of the parameters of the engine, not only do you change the rod length, you also change rod angles, ring drag, piston weight, piston pin height, ring stack height in some cases, crank counter weigh, piston dwell, exhaust scavenging timing etc.

If you take some time and actually calculate out , or do the math,what changes happen between lets say a 5.7” rod and a 6.0” rod on a 3.48” , or 3.75"stroke crank, in a 350 or 383 sbc.. You will soon see the actual amounts of the angle changes are very minimum. Then , your forced to ask your self how or even if these small changes in rod angle will affect the engines hp/torque, and to what extent, and will the changes be beneficial or hurt your results, and Id also point out that the compression and cam timing will also effectively change your results in some cases.

yes the internet is full of claims, claims that The motor will carry the power and torque curve father up into the rpm range with a longer connecting rod.
But you are forced to ask, by how much? and is the result , because of the rod length,change or because you used totally different lighter piston with a different ring package,and in many cases changed quench or compression etc. There are sure to be other changes that were required inside an engine with a rod length change, so you can't instantly conclude that the change in connecting rod length alone made the changes (IF ANY) you see on a dyno.

I doubt its even possible to build two virtually identical engines where only the rod length alone changed, not I personally have tried to install the longer rods and try to get a rod to stroke ratio as close to 2:1 AS OTHER FACTORS ALLOW.
this rod to stroke ratio,can be built with a 6" connecting rod and 3" stroke to build a 302 with a 283 crank and using a 327 or 350 4" bore block, or the same 283 crank in a 400 larger bearing size block with custom machined bearing spacers, to build a 4.155 bore and 3" stroke combo, correctly set up these combo are known to make very good horsepower per cubic inch, but theres no question that the added cubic inches of a 3.75" stroke crank far exceeds the results even with a less desirable rod to stroke ratio.
now a 350 with a 3.48" stroke with a 5.7' rod has a 1.64 rod to stroke ratio,
a 383 with a 5.7" rod has a 1.52:1 ratio
a 383 with a 6" rod has a 1.6"1 ratio and in every case Ive ever seen the increased displacement had a far greater effect on the 383 performance than the change in rod length seemed to induce.
as to connecting rods , from a mechanical limitations point of view, the rod bolts and the area they connect tend to be the connecting rod weak point, so Id strongly suggest ARP 7/16" rod bolts in cap screw rod designs, with the (I) beam in theory having a almost non-existent strength advantage IF THE ROD MATERIAL CROSS SECTION IS IDENTICAL, which it is usually not! I would simply suggest you shop carefully ,demand a 7/16" ARP rod bolt cap screw connecting rod of the length you prefer from a quality manufacturer, scat has been my connecting rod of choice for most engine builds


SBC
SCAT I BEAM
http://www.summitracing.com/parts/sca-25700/overview/

http://www.summitracing.com/parts/sca-2 ... /overview/


SCAT H BEAM
http://www.summitracing.com/parts/sca-6570020/overview/

http://www.summitracing.com/parts/sca-6 ... /overview/