how to size a 4-2-1 header for my SBC



how to size a 4-2-1 header for my SBC

Postby Carlos » November 29th, 2009, 8:24 am

Hi folks,

I read many of the links gumpy provided (THANKS, this gave new insights), but without saying I understood all of the stuff 100%, but I think I got the basics.

However, most of the articles reflect 4-1 headers design mainly. I did not find any calculator or maths for a 4 - 2- 1 header, so far.
As I am very restricted due to my space frame chassis and don't want to use sidepipes (must be street legal) I have to go with 4-2-1- design, with or w/o X-pipe.

My car is a SBC powered Cobra 2.300pounds, used for "street fun"

Engine spec:
a slightly modified ZZ3
.30 overboreTRW pistons L2304F30 ( should give CR 11:1 based on modified heads, accd to engine shop )

Ignition:
is MDS 6AL, will be controlled by Megasquirt MS-II soon.

Heads are ZZ3, ported by machine shop. I don't have flow rates, sorry.
Intake valve head diameter 2,02 Intake port dimensions 1.93 x 1.22
Exhaust valve head dia. 1,6 Exhaust port dimensions 1.38 height x 1.5 width, D-shaped"

Fuel system
TWM induction http://www.twminduction.com/
Individual runners, throttle size 48mm
Injectors Bosch #0 280 155 868
Fuel Pump Bosch #0580 464070 (3bar)
ECU: Megasquirt with MSEXTRA Code (Beta V3)

Cam
http://www.crower.com/misc/cam_spec/cam_finder.php?part_num=00471&x=16&y=5
Part Number/Work Order Number 00471
Engine Application 262-400 CHEVY
Grind Number 300R

ADVERTISED CAMSHAFT SPECIFICATIONS:
INTAKE: Duration: 286º Lift: .555 Clearance Hot: .000
EXHAUST: Duration: 292º Lift: .559 Clearance Hot: .000

The specifications listed above are based on a rockerarm ratio of 1.50 IN 1.50 EX (what I do have)

The information below is for degreeing cam only. Correct only at .050" tappet lift.
INTAKE Opens: 12.0 BTDC
Closes: 44.0 ABDC
EXHAUST Opens: 54.0 BBDC
Closes: 6.0 ATDC
LOBE SEPERATION 110º
Duration at .050" Intake: 236
Exhaust: 240
LOBE LIFT Intake: .370
Exhaust: .373

Transmission is 200R4 / 2.400 Stall by http://www.phoenixtrans.com/ (The best service I ever experienced in my gearhead live)
Rear end 3.31
Tires 275/55/15

So far i used a header design built for convenience, simply to save time. http://forum.grumpysperformance.com/viewtopic.php?f=2&t=2469&st=0&sk=t&sd=a&start=12
Now, as I'll add the TWM induction http://forum.grumpysperformance.com/viewtopic.php?f=2&t=2469&st=0&sk=t&sd=a&start=9 I want to built optimized stainless headers.

This is a project I have dropped several times, but now, due to the lowered engine mounts, which were required by the big TWM air horns, (didn't want to build a huge hood scoop) I have to build a new exhaust anyway.

If I have to sacrifice top HP due to design , I don't care too much, as long as the torque is kickin butt... :)

any help aprecciated

Carlos.

some historic data of the engine which might give you an idea how it runs.

dyno curves of my old setup with 48 Webbers and the exhaust I showed.
Image

1. ZZ3 stock engine, no mods except my Webber 48 IDF carbs
2. same as 1, but heads ported plus TRW pistons added CR 11:1
3. same as two, but CROWER CAM 471 LM added, plus block hugger headers 1 1/2 replaced by 1 5/8 and tubing from collector to H-pipe increased from 2" to 2 1/2"

1. 316 lbs ft @ 1.500 RPM, 319 hp @ 4.875 RPM
2. 425 lbs ft @ 1.875 RPM, 338 hp @ 5.500 RPM
3. 532 lbs ft @ 2.375 RPM, 361 hp @ 5.500 RPM

those days I used a TH350 with holeshot 2.400 stall
Last edited by Carlos on December 12th, 2010, 2:13 pm, edited 1 time in total.
If you can make black marks on a straight from the time you turn out of a corner UNTIL the braking point of the next turn, then you have enough HORSEPOWER
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Re: how to size a 4-2-1 header for my SBC

Postby grumpyvette » November 29th, 2009, 10:52 am

viewtopic.php?f=56&t=352

viewtopic.php?f=56&t=1166

http://www.slowgt.com/Calc2.htm#Header

http://www.bgsoflex.com/auto.html

http://www.spdexhaust.com/

viewtopic.php?f=56&t=495&p=29147#p29147

these threads might help
keep in mind that the efficiency of the headers scavenging the cylinders , and helping to draw in the following intake charge,is almost totally dependent on maintaining a very low flow restriction or back-pressure in the collectors ,especially at mid and upper rpm levels
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I calculated a 4-2-1 header design that would be close to the IDEAL for your application, but its most likely going to be HARDER to package into your clearance requirements than a 4-into-1 design,because the primary exhaust tubes are not much different in length and while it might produce more low and mid rpm torque it requires a longer total length than a 4--1 design
Image
http://www.pontiacracing.net/js_header_length1.htm

notice theres some potential too both increase the effective length of the primary tubes to gain lower rpm torque and increase ground clearance slightly under the car with the 4-2-1 exhaust config on the primary pipe headers

Image
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: how to size a 4-2-1 header for my SBC

Postby Carlos » November 29th, 2009, 12:43 pm

grumpyvette wrote:I calculated a 4-2-1 header design that would be close to the IDEAL for your application, but its most likely going to be HARDER to package into your clearance requirements than a 4-into-1 design,because the primary exhaust tubes are not much different in length and while it might produce more low and mid rpm torque it requires a longer total length than a 4--1 design

Keen to see the dimensions ;)

Total lenght is not my major concern, my major concern is to have a pack of four tubes underneath the car, where clearence to road isn't really big.
To avoid having two tubes above each other and two beside each others, (the typical 4-1 collector merge) a buddy was doing a "flat 4 design" with 4 tubes beside each other merging into the collector.

I doub't this is a good design, as I read collectors design is crucial to performance, so I was hoping to be able to merge from 4 into two tubes before the tubes go under the car.

C.
If you can make black marks on a straight from the time you turn out of a corner UNTIL the braking point of the next turn, then you have enough HORSEPOWER
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Re: how to size a 4-2-1 header for my SBC

Postby grumpyvette » December 1st, 2009, 1:20 pm

theres two routes you can go, the obvious route is to look at the packaging constraints placed on you by the cars clearances and build a header designed to fit and function within those clearances with compromised dimensions & lengths ,and build a header that's some what shorter in length but reasonably easy to fabricate and install, which is exactly what most commercial header manufacturers will do, OR you can look into the physics and math and find out what will be most beneficial for the engines operational power band
when you look into the math...all the calculators suggest a primary header tube of between 37-39 inches in length and no larger than about 1.75" diam. you then have a choice of collector designs and most calculators suggest between a 18"-20" 3" DIAM. COLLECTOR , NOW IF YOU WANT TO GO THE 4-2-1 ROUTE you can maximize the torques by having a (Y) added to the 37-39" primaries, before they extend into a common collector, which will add to the low rpm cylinder scavenging effect, by keeping the exhaust velocity high for a longer time, if so the (Y) would probably need to be about 15" long and go from the twin 1.75" primaries to about a single 2.25" secondary , having the junction located at the 38" length from the exhaust valves, and extending on that extra 15" where it enters a 3" collector,(Y) where the two 2.25" (Y) pipes join a larger (Y) OR you can give op a bit of low rpm efficiency but gain some mid range by placing the junction closer to the exhaust valve, but I would not even consider a primary much shorter than 18"-22", if your goal is low rpm torque.
but keep in mind that your current shorty block huger headers allow the car to run high 11 second times, you could easily gain 15-30, maybe more hp with the better headers, you could also add some extra low and mid rpm torque, but at some point the cost vs the benefits gets to be rather pointless, keep in mind that with your current header and tail pipe design the whole exhaust pipe length is acting like a header collector and reducing any back pressure will give benefits in increased horsepower

viewtopic.php?f=56&t=352

viewtopic.php?f=56&t=1166

http://www.slowgt.com/Calc2.htm#Header

the very first thing ID suggest is getting a back-pressure gauge installed on your exhaust pipe and measuring the exhaust back-pressure, at the upper rpm range, if its much above 2 psi your mufflers may be hurting you more than the headers, your dyno curve strongly suggests that the exhaust or the headers are restricting your power in the upper rpm range, as theres a noticeable decline in the rate of increase in power, by about 3250rpm, while that cam should pull hard to 6000rpm

viewtopic.php?f=56&t=495&p=2008&hilit=+back+pressure#p2008
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

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Re: how to size a 4-2-1 header for my SBC

Postby Carlos » December 13th, 2009, 11:38 am

here is a quick update on my headers project:

Thanks to grumpy and vince from burnsstainless, I made the decision to build a 4-2-1 set of headers.
I will use use burnsstainless 2-1 merge collectors.
http://www.burnsstainless.com/MergeCollectors/2into1base/2into1base.html
I simply don't have the time to build 6 of them. I think pricing is OK, if you see the effort you would have to spend to build them.

back to basics:
First I had to get corect measures of my exhaust flanges. How to do ?
I figured out that none of the many gaskets for D-shaped SBCs are matching well.
So..
I used a sheet of wood to make a "print" of the exhaust ports.
First cleaned the head, then used a felt marker to blacken the exhaust ports sealing surface.
Bolting the wooden shet to the head, then hammered on it to get the "print.
Then I took measurements of the "wooden print", and made a 3D drawing.
Sent by e-mail to a buddy. He made a first sample flange of 18 gauge sheetmetal, by lasercut.
Bolted the sheetmetal to the head to check how good my measurements worked out.
Corrected 3D drawing slighlty.
Done.

Next thing I worried about was how to build "sample headers".
The "LEGO style" stuff for making prototypes is just too expensive for me.
So I simply used flexible PVC tubes which can be bent easily if warmed up by a heat gun http://www.steinel.net/products/heatguns/electronic_heatguns.cfm
It took me only one hour to get the first set of sample headers, which will serve as a baseline to check routing and different legths, which shall be corrected.

keep you posted
C.
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Re: how to size a 4-2-1 header for my SBC

Postby Carlos » December 13th, 2009, 11:40 am

the very first sample headers
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If you can make black marks on a straight from the time you turn out of a corner UNTIL the braking point of the next turn, then you have enough HORSEPOWER
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Re: how to size a 4-2-1 header for my SBC

Postby grumpyvette » December 13th, 2009, 12:48 pm

viewtopic.php?f=56&t=961&p=1654&hilit=smurf#p1654



that looks good!
btw did you read this thread above ?

btw, looking at your mock -up reminded me of these, which might fit, or be easily modified to fit your application

http://www.summitracing.com/parts/HOK-2 ... mage=large
Image
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: how to size a 4-2-1 header for my SBC

Postby Carlos » December 13th, 2009, 6:00 pm

grumpyvette wrote:http://forum.grumpysperformance.com/viewtopic.php?f=56&t=961&p=1654&hilit=smurf#p1654
that looks good!
btw did you read this thread above ?

yep I like the foam trick, but unfortunately it won't work in my setup.
I will have to cut the primaries apart in the vertical section, as I cannot (by less than an inch) pull them out through the spaceframe chassis when they are bundled in full length.
So I might have to use a 4 hole flange.

grumpyvette wrote:btw, looking at your mock -up reminded me of these, which might fit, or be easily modified to fit your application

Thanks !
The right one really gets close, I need to check out the left one a bit more in detail. It looks as it will interfer with my frame.
Even if it is a 4-1 I will check and do some guesswork on fitting.

C.
If you can make black marks on a straight from the time you turn out of a corner UNTIL the braking point of the next turn, then you have enough HORSEPOWER
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Re: how to size a 4-2-1 header for my SBC

Postby Carlos » December 17th, 2009, 1:30 pm

My flanges are done,
here is how I made the D-shaped port fitting the round tube.
The round primaries tube, as you can see, will not remain round, as the clearence to the bolts would be to narrow.
To avoid an adapter flange, I decided to make them a bit oval.
I know there is a slight restriction at the lower edges of the port, seen from head, but I value this as irrelvant.

The drawing should give you the option to turn and magnify as you want.
You can download the exe file here
http://www.cobra-roadster.com/ac427de/public/exhaust-flange-SB-ZZ3-head-V2.exe
regards
C.
Last edited by Carlos on December 17th, 2009, 2:28 pm, edited 1 time in total.
If you can make black marks on a straight from the time you turn out of a corner UNTIL the braking point of the next turn, then you have enough HORSEPOWER
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Re: how to size a 4-2-1 header for my SBC

Postby grumpyvette » December 17th, 2009, 1:37 pm

IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

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Re: how to size a 4-2-1 header for my SBC

Postby Carlos » December 17th, 2009, 2:30 pm

pls try the link again, I removed the blanks in the filename which might be interpreted wrong in a non german character set.

C.
If you can make black marks on a straight from the time you turn out of a corner UNTIL the braking point of the next turn, then you have enough HORSEPOWER
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Re: how to size a 4-2-1 header for my SBC

Postby Carlos » December 17th, 2009, 2:48 pm

As things become more clear during conrete building preperation, and things turn out to be feasible or not... here is another question
I read 4-2-1 designs are sensitive to firing order, but I don't have an indication what this really means in terms of HP / torque.
I don't know yet which cylinders would have to be connected into one Y, but worst case I'd have to route from one side to the other.

So... is it worthwhile to route the primaries underneath the engine from one cylinder bank to the other, or is this effort more of "philosophical value".
Any input aprecciated.

C.
If you can make black marks on a straight from the time you turn out of a corner UNTIL the braking point of the next turn, then you have enough HORSEPOWER
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Re: how to size a 4-2-1 header for my SBC

Postby grumpyvette » December 17th, 2009, 4:25 pm

in an ideal world the exhaust pulses in each (Y) in a custom header will be evenly spaced as they enter the header collector, to equalize the exhaust pressure and restriction to flow...look carefully at the diagrams, below.
but in the real world the improvement that results in horsepower from a true 180 degree header, is in most applications, not financially worth the gains vs the cost or practical from a manufacturing or ease of installation, or clearance issue.
now there are gains to be had but chasing the last possible potential hp, is rather a waste of money considering that there are far less expensive and easier ways to gain hp, that will fit and function, such as better cylinder heads, nitrous, turbos etc.

Image
Image
Image

SBC cylinder numbering;
-2-4-6-8
1-3-5-7


this is what you would need to build, but look closely, your frame clearance and oil pan, to road clearance will be a huge consideration in the design
Image

http://www.stahlheaders.com/docs/2006catalog.PDF
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: how to size a 4-2-1 header for my SBC

Postby Carlos » December 17th, 2009, 5:50 pm

grumpyvette wrote:this is what you would need to build, but look closely, your frame clearance and oil pan, to road clearance will be a huge consideration in the design
Image
http://www.stahlheaders.com/docs/2006catalog.PDF


OK, within a second you convinced me to go back to the 4-1 design... :)
remember - I intended to go 4-2-1 due to space restrictions. I would have to convert to dry sump to allow this design.

So if the above is the ideal 4-2-1 design, which will btw never allow the calculated length of 24" primaries (to me it looks more like 40"+), I'll drop this design and go back to 4-1. Need to check how long my 1 5/8" primaries will have to be.

seems to make life really easier, but its always good to check out the options.
txs
C.
If you can make black marks on a straight from the time you turn out of a corner UNTIL the braking point of the next turn, then you have enough HORSEPOWER
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Re: how to size a 4-2-1 header for my SBC

Postby Carlos » January 3rd, 2010, 5:54 am

just an update...

First of all " Happy New Year" to you folks.

I checked again how to route 4-1 headers, seems to be very tricky (too tricky for me :) ) with my spaceframe chassis.
So... I am back to the tri-y setup.
Pairing 1-5, 3-7, 6-8, 4-2.

I ordered the merge collectors from http://www.burnsstainless.com.
I found the folks at burnsstainless very knowledgable and helpful, special thanks to Vincent.
Here are the dimensions of my setup, calculated by Vince:
http://www.cobra-roadster.com/ac427de/public/tri-y-headers.jpg
Looking forward to see the stuff arriving in a few days.

As a "side effect" to the lowered engine, which itself was a "side effect" of my new induction :lol: , I also had to redesign my alternator setup. Yes I had built a special some years ago already, but due to the new intake of my TWMinduction ,I am able to drop the vacuum pump which was sitting at the back of the old alternator... http://forum.grumpysperformance.com/viewtopic.php?f=2&t=2469

I moved the alternator from low @ passenger side to low @ drivers side. As the brackets offered by Summitracing or Marchperformance etc. did not fit (my spaceframe is in the way again) I built a set of new ones.
That is how it looks now.

C.
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If you can make black marks on a straight from the time you turn out of a corner UNTIL the braking point of the next turn, then you have enough HORSEPOWER
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Re: how to size a 4-2-1 header for my SBC

Postby grumpyvette » January 3rd, 2010, 8:35 am

tight engine compartments on smaller cars like your COBRA and MY CORVETTES are ALWAYS a P.I.T.A. when it comes to clearance for accessories and exhaust, but that's part of the challenge your faced with when you select a smaller lighter weight car
I,M impressed with the thought your putting into the modifications and the fabrication skills your displaying here, it looks like a really nice car your building, that most guys can only dream about owning
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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