Headers

[SappySE107]

Found some pics...

http://www.60degreev6.com/images/DOHC/Perf/Headers/

[Anonymous]

Marty, I think that there will be a difference in primary length on a DOHC and pushrod motor of the same size. Im not entirely sure WHY that is, but it may have to do with the exhaust pulses?

[RacerX11]

If both the pushrod and DOHC are putting out the same power, the dimensions should be the same. The exhaust pulses aren't going to be any different due to the two vs. one exhaust valve. All of the calculations I have seen rely on engine displacement, power output, primary diameter, and peak rpm. The DOHC might require different length based on its higher power potential due to the better breathing capabilities of the 4-valve heads, but if you compare to an equal power OHV engine, the differences are minimal.

Based on my experience with Formula SAE induction and exhaust design, you can run all the numbers and equations and calculations you want, but to definitively find the optimum design, you will need to run lots of different combinations on a dyno. This just isn't practical for a street car (unless one of us wins the lottery anytime soon :-) The combo that may look good on paper doesn't always turn out to be the one that performs best in the real world.

My biggest point is that 36" primaries could be optimal for this engine, but would 26" primaries lose that much power? It would certainly make it easier to package in the FWD engine compartment, and still outperform the stock cast manifolds.

Marty

[Anonymous]

Thats exactly right Marty. Even 16" primary headers would probably have gains over the stock POS's. We aren't really arguing that. What we are talking about is getting the MOST out of headers because its probably a huge PITA to make them... therefore you will only want to make ONE set. (Not saying you are wrong in any way, Marty. Just stating the intentions.)

[Anonymous]

Also, Marty, do you have more pictures of your headers? I'd like to see them unwrapped.

[3.4Z24]

a 3" pipe has a cross sectional area of 7.07" squared
a 3-1/2" pipe's cross sectional area is 9.62" sqared
2 2-1/8" pipes combine to an area of 7.09" squared
2 2-1/4" pipes combine to an area of 7.95" squared
2 2-1/2" pipes combine to an area of 9.91" squared

i used 3-1/2" single exhaust after the 'y' on my '85 z28 and that made it very happy.

[3.4Z24]

by the way, i just calculated all that as the inside dimension of the pipes, but you get the picture. just use pie x the squared radius...

i've seen a lot of power pushed through single 3-1/2" exhaust on many v8 f-bodies. i think a single 3" on our little sixes would be plenty-that compares to two 2-1/8" pipes.

[brian89gp]

Another thing to think about with the primary length, is the longer length and few extra HP worth the hassle? If they get long enough you may have to remove the headers to do regular maintenance which would not be good.

And on the same note, design them so they can be removed with the engien still in the car. If you have your engine out and make the headers it is easy to forget about this.

[Streetrodder83]

From several things that I have read and past experiences. Is that the higher reving engines tend to like shorter primaries. Because the shorter primaries favor the upper range of the powerband. How short or long they need to be, comes back to the same problem of needing to build several sets to test. But atleast if you stick to mild steel, the cost won't be too bad, it's pretty cheap. Burns Stainless makes 3 into 1 merge collectors, that would be helpful as a jig, depending on primary size the cost varies but for 1.5" is like $197 for a mild steel, about $30 more for stainless. Something like that could help to ease the process in constructing the headers.

[Anonymous]

Got any links to sites that sell the tubing? This weekend I'm gonna go out and buy some flex-tubing like shown here: (to mock up what the front header could fit like)

[Streetrodder83]

It depends on what material you want you can go to www.burnsstainless.com for 304 and 321 stainless, titanium, and Iconel. That is all pretty expensive stuff, I used to have a name of a local metal supplier. I can get a hold of someone tomorrow to get the name and number, since you are in relatively the same area I am. It would be cheaper and you can get the mild steel tubing.

[Streetrodder83]

Also, if you do chose the more exotic materials. I am hopefully going to be picking up a TIG welder sometime next month, if you don't have access to one.

[RacerX11]

Also, Marty, do you have more pictures of your headers? I'd like to see them unwrapped.

I have some more pics from different angles, and with them off the engine, but I don't think I have any of them unwrapped. I didn't get access to a digi cam until after they were done. I'll post more this afternoon.

Marty

[RacerX11]

by the way, i just calculated all that as the inside dimension of the pipes, but you get the picture. just use pie x the squared radius...

i've seen a lot of power pushed through single 3-1/2" exhaust on many v8 f-bodies. i think a single 3" on our little sixes would be plenty-that compares to two 2-1/8" pipes.

I agree. My '99 Z-28 comes stock with 2-3/4" mandrel-bent single pipe, and it put over 300HP to the wheels. I think even 3" is overkill on even a well-built six, but 2-1/2" might be too small, and 2-3/4" isn't very easy to get aftermarket. I am running my headers Y-ed into a single 3" for my 3400 SC. It should be plenty.

Marty

[RacerX11]

Try www.headersbyed.com for parts. Burns has some great stuff,but they don't carry mild steel anymore. Ed carries mandrel bends, collectors, and flanges (although not for the DOHC head). I picked up all of my stuff from him, and I am very pleased with the quality of everything. He also has some good reading material on header design and construction.

Edit: JC Whitney also carries mandrel bends, both mild and stainless. I have only used their 2-1/4, 2-1/2, and 3" sizes, so I don't have any experience with their smaller pipes. Their bigger stuff is not of the same quality as Burns or Ed, but the prices are much cheaper.

And Brian is right: install is very important. I can't remove my rear header without unbolting the motor mounts and tilting the engine forward. There was no wayaround it.

Marty