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



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

Postby Carlos » January 3rd, 2010, 12:01 pm

grumpyvette wrote: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


Thanks for this.

I am displaying some of my stuff for three reasons...

First:
To demonstrate putting thought into a project upfront can avoid big surprises - don't we all know the situations when a "simple" project is running out of time and budget...
I am currently in one of those: "Wow, let's put a nice TWM induction on the engine, replacing the Webbers" - this was the beginning.
In addition I need: new engine mounts due to height of the intake runers, leading into new headers, smaller distributor due to lack of clearence, new alternator / -brackets / -harness, relocation of oil filters, relocation of fuel supply and so on ;)

Second:
I want to help motivate guys thinking beyond the stuff which simply can be bought. This sometimes makes things possible which, at a first sight, are impossible. So your project, which is even more special then, will be possible.
It does not always need big $$$, i.e. the alternator brackets I made. US$ 15.- for the material and six hours of work.

Third:
I also received lots of hints and information out of the internet and do aprecciate big time the effort other folks are putting into the forums.

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 » February 3rd, 2010, 3:14 pm

3D CAD drawings became reality....

the final stainless flanges, laser cut, have arrived :D

bad part of the story is...this means lots of work now.

As you might have discovered, ports are D-shaped on cyl head side, oval on the header side. Also I added kind of a small countersink to ensure tubes will stay in place when welding.

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

Postby grumpyvette » February 3rd, 2010, 3:22 pm

IM looking forward to see pictures of the finished product,
just remember, something I learned building headers, measure very carefully and cut only after marking and double checking measurements carefully, and only tack weld until everything lines up and clearances are carefully verified

these threads and sub links might help

viewtopic.php?f=56&t=1166

viewtopic.php?f=56&t=352

viewtopic.php?f=60&t=1283

viewtopic.php?f=60&t=1108

viewtopic.php?f=56&t=260

viewtopic.php?f=56&t=2002

Ive seen very little difference in power results, from decent header designs if all the primary tubes are within about 2" (5 cm?) in length, that what I generally feel is acceptable , don,t go slashing your wrists, or jumping out of sky scraper windows if one tube needs to be a bit shorter or longer,or even loose much sleep, but naturally the closer the better.
the main thing is getting the bends smooth and the headers looking decent, and having them fit the car with correct clearances
and try to get the welds looking nice and the basic design having the nearly correct length on both the primary and collectors, but keep in mind if the exhaust beyond the header collectors is restrictive your wasting a great deal of the headers potential to effectively scavenge the cylinders

btw mocking welds, and test fitting, up lengths of pipe during the fabrication process , with tack welds or even duct tape is something you won,t be the first guy to do

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 » July 21st, 2010, 3:11 pm

Hi,
finally after many hours of cutting, grinding welding I am done with the right side.
Left side is supposed to be completed within the next two weeks.
IDue to the space frame I had to make some compromise, e.g. one runner is 2" longer than ideal, but.. so what I guess on my engine this shouldn't hurt too much.
I also had to make this runner detachable, to be able to remove the header.
So I simply went to the lathe an made a slip in piece. Real snug fit, with a bit of gun gum, no clamp required.

Really looking forward to have the baby back on the road and hear (feel :mrgreen: ) the sound.

As I added the TWM induction 48mm during winter also, it should kick butt a bit more also.

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 Carlos » July 21st, 2010, 3:19 pm

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

Postby grumpyvette » July 21st, 2010, 3:23 pm

could you please post pictures of the finished headers from under the car and from both sides so we can get a better feel for the whole install, once its up and running?

building headers is a very time intensive project and knowing how to welt especially TIG weld is a great asset.

IVE been saving for a set of these

viewtopic.php?f=56&t=352&p=433&hilit=legos#p433
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 » July 21st, 2010, 3:23 pm

getting the stuff done

Hi Grumpy, yes I'll post some more pics from the other side and underneath as soon as it is running.

Tried to save for "the Legos" as well, it must be fun to design with them, but I felt I was running out of time before having the budget...so I went down the painful route ;)

regards

C.
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Last edited by Carlos on December 12th, 2010, 1:57 pm, edited 2 times 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 » July 21st, 2010, 6:52 pm

its always mildly amazing and a bit frustrating, how complex the simple routing of a few header primary pipes can become once you need to snake them around suspension and roll cage components in a tight engine compartment, especially if your trying to maintain a semi similar length on each tube, but you look like you've done a good job, and your sure to have gained experience that will prove very useful in the future.
every time I build custom headers I get a bit better at it, gain a bit more skill with a welder, a good deal more skill at cutting tubing and measuring angles, accurately, and usually swear Ill, never do it again, but theres a great deal of satisfaction in doing the job correctly and you'll be surprised at the difference well designed headers can make in your torque curve.
the result seems to be that you constantly feel that the last set you built could be improved upon and in almost every case thats not only correct but you see how, you could have done so, yourself after you've finished each set, so, you look at each set as less than ideal, but the truth is that after a few sets you gain enough basic skill that the gains you make at first are very noticeable, but as you progress , and gain skill in both the planing and fabrication, stages you produce better and better headers, and making major improvements becomes a bit harder to do.
keep in mind most factory headers are designed with ease of fabrication, and low cost and easy installation as the primary goals

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

these threads might help

http://metalgeek.com/static/cope.pcgi

http://www.pontiacracing.net/js_header_length1.htm
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 grumpyvette » July 21st, 2010, 7:21 pm

viewtopic.php?f=60&t=3158&p=8431&hilit=roll+cage#p8431

btw anytime you get the least feeling you can,t weld.....................look thru this thread above its sure to make you feel better about your skill level, I know it brought a big grin to my face seeing how badly it really can be done!
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 » August 6th, 2010, 10:39 am

Both headers are done, looking forward to get them installed tomorrow :D
as you might reconize in respect of length I connected the long primaries to the short bends of the collectors 4-2-1, and vc vs the short primaries to long bend of the collectors. Also firing order has ben taken into account.
Hope this all back the effort at the dyno.
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 » August 6th, 2010, 3:31 pm

its always Impressive, to see the amount of work required and the details of that work that was required to build custom components, especially engine and related components ,especially when you considered, that you need to work around the frame,suspension and engine to get headers to fit and still try to maintain semi-equal length tubes.
many guys would have tried to do that custom fabrication work and given up after a couple hours ,after realizing its not nearly as easy to do as it at first might appear to be, I think you did a really nice job for a first try!,Id point out that Ive seen many sets that looked far less well done, produced from supposed pro-muffler shops, whose main goal was making a profit , which is as I,m sure you know now an unlikely prospect once you start counting the time and materials required,to fabricate headers that fit a custom installation with suspension and frame components blocking the easy routes
if you get a chance, after those headers are installed, let us know your impression of both how the car sounds and how it runs and accelerates
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 12th, 2010, 1:55 pm

header job is done :D
Cobra is waiting for the final tune next spring...
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
Carlos

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

Postby grumpyvette » December 12th, 2010, 2:05 pm

can you list your current engine component, list of parts?
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 12th, 2010, 2:17 pm

grumpyvette wrote:can you list your current engine component, list of parts?


I listed tech spec at the beginning of this post, just added the ECU/EFI part, mechanical stuff remaines unchanged.

If you have some spare time... I would be interested about HP & torque of my combo, calculated by your desktop dyno ;o)
As I will do the final tune in spring, your calculations could be a teaser...

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 12th, 2010, 2:51 pm

Image

here my software dyno prediction based on what youve posted, it will be interesting how close the software dyno, wild guess comes to reality
(470 FLYWHEEL hp at 5500rpm/500 FLYWHEEL ft lbs at 4000rpm)

thats about 386hp/415 ft lbs at the rear wheels

assuming your weight adds about 200 lbs to the car......getting into the low 11 second range or high 10s in the 120mph or a bit more certainly seems do-able


http://www.race-cars.net/calculators/et_calculator.html
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 » March 25th, 2011, 5:21 pm

grumpyvette wrote:assuming your weight adds about 200 lbs to the car......

You seem to have a webcam...pretty close :D

The calculation looks promising - Thanks a lot.

On the other hand...I guess my transmission will give up w/o an upgrade.
It is a custom made 200R4 with custom made stall converter, was built it to withstand 400hp.
I was going with the small trans due to space restrictions those days.
Guess I need to speak with Greg @ phoenixtrans.com, he offers world class service, even to me over here at "world's end".

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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