Ok youve decided to buy/build a 383 from parts youve collected from that 350 in your car, youve got the parts an your iching to start assembly....should you take the time to ballance the parts or just slap it together....
ballancing/clearancing the rotating assembly will effectively reduce the stress on the components, the amount that stress will be reduced depends on how far off the components are from the orriginals the crank,damper and flexplate or flywheel were designed for , now I think ballancing the new assemblys a NO BRAINER as its usually under $200 and even if it reduced the stress only 15% its a big improvement, but the truth here is that without reballancing youve more than likely got zero idea how far off the new parts are and you might be assembling a combo that will shake itself to pieces in 10K......Id suggesst spending the $200 and getting it done correctly.

yeah! we all know guys that skip the ballance work and run engines, we all also know guys that have constant freak engine and drive train breakage and tunning, and oil control issues/ problems, with thier cars and can,t seem to locate the source.
you can spend $150-200 in most cases up front to prevent problems or a take a chance on spending a good deal more once they occure, your choice!
and Id figgure the chances are about like playing russian roulette with two or three cylinders loaded in your revolver.

the next question that comes up,
("can I re-use my 350 damper and flexplate or flywheel ?")


that depends on several factors, 3.75" stroke cranks come in BOTH internally ballanced and EXTERNALLY BALLANCED designs, the 400 crank cut down to use in a 350 block is externally ballanced and requires in most cases a 400 damper and flexplate or flywheel, if the cranks designed for an EXTERNALLY ballanced flexplate and damper like a 400 has ,you CAN get it RE-ballanced for a INTERNALLY ballanced flexplate and damper like a 350, so that you can use internally ballanced components like a 350 damper and flywheel/flexplate... but the cost is frequently higher than just buying a new crank of the correct design, generally your stuck using the type of ballance the cranks originally designed for due to counter weight size, placement and cost issues, as welding in extra mallory metal weights gets expensive fast, and forged 3.75" SBC internally ballanced cranks are not all that expensive. theres also the option of installing counter weights on the 350 components to use with the 400 crank, if you choose to go that route




http://www.scatcrankshafts.com/


theres a DIFFERANCE between CAN, you physically do something and CAN you do it at a reasonable cost!
I know of no-one that will take the time and effort and go thru the expense to modify a 400 crank to run 350 components because an INTERNALLY ballanced 3.75" stroke crank thats designed to run those 350 components is fairly cheap and easily obtainable, but a decent shop can weld up counter weights and add enough mallory metal to reballance almost any crank to internally ballance it

The chevy v8 flywheel or flexplate usually has seven holes in it. 6 for bolts and one for a locator dowel pin, which can be missing, on some cranks.
on the mount flange in the back of the crankshaft, so the flywheel will bolt on 6 different ways if the dowel pin is missing as the bolt hole spacing is the same. Check to be sure the dowel pin hole in flywheel is aligned with the dowel hole in the crankshaft flange, if the pins missing, or its will unballance the assembly.


Ive always suggested buying a complete ballanced rotating assembly from a single name brand source like LUNATI , CROWER, SCAT,OLIVER,EAGLE, HERBERT PERFORMANCE,OHIO CRANK, or several other sources, but even supposedly factory ballanced assemblies need to be checked as Ive seen some (SUPPOSEDLY BALLANCED) assemblys that were obviously just matched weight components

will this help?
IT will if you take the effort to read thru the linked INFO

http://victorylibrary.com/mopar/crank-bal-c.htm

http://www.circletrack.com/techarticles ... index.html

http://www.centuryperformance.com/engin ... g-145.html

http://victorylibrary.com/mopar/crank-bal-c.htm

http://www.centuryperformance.com/engine-balancing-for-life-power-amp-efficiency-spg-145.html

http://www.torquecars.com/tuning/engine-balancing.php

http://www.eddiesvalvegrinding.com/balancing.htm

http://www.completeautorepair.net/engine_balancing.htm

http://www.babcox.com/editorial/ar/eb10330.htm

http://www.carcraft.com/howto/ccrp_0803_engine_balancing/index.html

http://www.fordmuscle.com/archives/2008 ... /index.php

http://www.fordmuscle.com/archives/2003/09/stroker/

worth reading thru


you can build an internal or externally ballanced engine, just because the stock 400 and 454 chevys are externally ballanced in no way prevents you from building a 383,396, 406 sbc or 454,496,540,572 BBC thats INTERNALLY BALLANCED, its just generally more expensive to do so.
Ive found that buying complete ballanced rotating assemblies from a single source is usually the best route, you can get either internal or externally ballanced assemblies, it helps a great deal to use light weight tool steel piston pins, pistons and (h) rods to lower the rotating/reciprocating weight, if you want to internally ballance the assembly.

parts sources

PHONE: 310-370-5501

http://www.scatcrankshafts.com/

http://www.adperformance.com/index.php?main_page=product_info&cPath=71_231&products_id=669

http://www.dougherbert.com/

call and ask if they have a complete ballanced assembly available
if your not sure of how an engine was assembled or the components or clearances that were used your choices are, run it as it arrived and pray.....or take the time to disassemble and verify everything in the assembly is as it should be.
most 400 sbc engine use a externally ballanced assembly, simply because that cheaper to produce and it costs less, but you can certainly build an internally ballanced 383-400-406 sbc or 454,496,540,572 BBC thats INTERNALLY BALLANCED, its just generally more expensive to do so.
from easily available components, yet its usually the best route as the internal engine stress levels, and harmonics induced in the rotating assembly, in the upper rpm ranges tends to be lower

no you can,t guess or just assume its correct, you'll need both matched components and the local balance shops tender care here if you want the engine to run smoothly unless you buy a factory matched set of components OR buy an aftermarket rotating assembly that comes as a balanced assembly.
BUT a word of caution, some of the so-called BALANCED assemblies are BARELY in specs and really need to be carefully rebalanced, ask for the component weights and if it was balanced to a 1,2,3 or gram tolerance, naturally the closer the better.

INTERNALLY BALANCED ASSEMBLIES induce LESS STRESS on the rotating components because EACH counterweight on the crank counter balances the components near it, EXTERNAL BALANCING takes into account the total imbalance of ALL the components along the cranks length, and adds enough weight to make the AVERAGE of all those combined IMBALANCE CONDITIONS CORRECT

just as a concept,you might want to think of it like having a long section of chain, that you want to keep stretched tight, and not allow to twist,or bounce around, you can either put one large bungee cord on each end (EXTERNALLY BALANCED)

or you can put two smaller bungee cords on the ends and 3 smaller ones on the 1/4, 1/2 and 3/4 length points along its length, (INTERNALLY BALANCED)
BOTH ARE FAIRLY STABLE but the difference is in the movement the central section sees, and the more movement and the more stress the metal in the crankshaft and the block holding it needs to absorb.
while that's hardly exactly whats going on the basic concept might help you visualize the difference.
IF that doesn,t help try this,
get out a strand of SPAGHETTI and draw a line along one edge with a black marker, now hold one end solid and twist the other end by spining in back and forth between you fingers, you'll see the line drawn start to spiral,(EXTERNAL BALANCE) then have a buddy hold the central area on the strand of SPAGHETTI in two places and repeat, the twisting , youll notice the deflection is greatly reduced, thats similar to what internal ballancing does with its larger counter weights.




http://store.summitracing.com/partdetai ... toview=sku
typical internally balanced components


typical externally balanced components below, notice the weight on the lower right area.




theres also weights available to change internally ballanced components to external should you want to go that route


ITS ALMOST ALWAYS A BETTER IDEA to buy a matched balanced kit with all components supplied from a single source
heres a few IVE used with good results


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

http://www.dougherbert.com/enginecompon ... 5f1f37f9e5

http://www.adperformance.com/index.php? ... ath=71_231
an EXTERNALLY balanced damper


its REQUIRED to be used with a MATCHING crank and counter weighted FLEX PLATE or FLYWHEEL

INTERNALLY BALANCED (SCAT, or LUNATI, or CROWER) 4340 steel FORGED KITS WITH 7/16" ARP rod bolts and clevite (H) bearings, and forged pistons are preferred in most cases, the scat 9000 cast steel cranks work ok for mild performance applications but INSIST on 7/16" ARP ROD BOLT RODS and ID strongly suggest INTERNAL BALANCING

forged components are generally stronger
(IE will take abuse longer and at greater stress levels) and forged pistons are slightly more heat resistant than hypereutectic or cast
as a general rule if your going to exceed 100hp shot of nitrous or have the rotating assembly spin at near 4000 feet per minute in piston speed forged components tend to be a good investment

viewtopic.php?f=53&t=110&hilit=4032

viewtopic.php?f=53&t=343&p=1170&hilit=redline#p1170

viewtopic.php?f=53&t=204&p=239#p239

http://www.centuryperformance.com/engin ... g-145.html

http://www.ghbalancer.com/techinfo/norm ... ion%27.htm

http://www.enginebuildermag.com/Article ... rofit.aspx



a reasonable limit on cast pistons usually falls near 4000 feet per minute in piston speeds
so your stroke is a factor not just rpms

http://www.csgnetwork.com/pistonspeedcalc.html

a balanced set of quality forged pistons can probably handle 4500fpm, or a bit more

If your thinking of interchanging components on a sbc, you'll need to know what your dealing with, I.E. internal or external balanced rotating assemblies, many 383 cranks are externally balanced ,meaning both the flex plate or flywheel and balancer are matched sets , with offset counter weights to compensate for a crank thats got smaller than ideal conter weights on its throws ,balancing the crank as it flex's,while almost all 350 cranks are internally balanced making interchanging the dampers a major problem, yes there are internally balanced 383 rotating assemblies and if you have one then theres a good chance the balancer could be used or an aftermarket balance weight can be added to a internally balanced assembly but it requires re-balancing to get it dead on correct and usually costs more than buying the correct damper to begin with

http://forum.grumpysperformance.com/viewtopic.php?f=53&t=562

http://forum.grumpysperformance.com/viewtopic.php?f=53&t=279

Grumpy,do you have any opinions on heavy versus lighter pistons and different size ring packs ??
Guy

use of lighter weight components reduces inertia, and resulting stress but taken too far it reduces strength of the components past the point where it is worth doing.
if your going to build a combo to run pump octane fuel that spends 90% of its time under 5500rpm and run a flat tappet cam, and an intake and heads designed for mid rpm torque, its rather pointless,
I don,t think theres a great deal gained on any street/strip application selecting light weight components past the point of selecting good quality forged components,
as an example,
like rods with the longest easily used length with 7/16" ARP L19 rod bolts
and 4340 forged steel cranks
and decent forged pistons with light weight piston pins,
remember its the total combo, its senseless to worry about grams in a piston when your trying to haul hundreds of extra pounds in a street car, in a 9:1-10:1 cpr engine thats geared mostly for decent mileage that gets to spend 90% plus of its life at under 5500rpm,now if your building a dragster thats going to spin 8700rpm thru the lights, and weight under 2100lbs running 13.7:1 compression and a solid roller cam and launch off the line at 5000plus rpm,then hit the nitrous, so it spends 90% of its time between 5000rpm and 7000 PLUS rpm,thats a totally different deal

one fairly common questions I get is about if swapping from a 35lb steel flywheel to a lighter 20lb aluminum flywheel, will help the acceleration in a 3500 lb muscle car used on the street,(IT WON,T), think about it, yes if you rev the engine in neutral it will spin up a bit quicker, but your NEVER in neutral when applying power to the rear wheels, and while the engines trying to accelerate 3500 lbs, the inertia of a 35 lb steel flywheel tends to retain energy, smooth shifts and store energy thats used in launching the car, while an aluminum flywheel might allow the car to accelerate marginally faster the trade off is seldom in the lighter flywheels favor once the et is compared.
now put that same flywheel swap into a 2300 lb circle track car that shifts constantly coming into and out of corners, and uses the engine compression to brake the car coming into corners on a short track,and blasts out of those corners at full throttle, and then yes the aluminum flywheel and light weight rotating assembly has a purpose.

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