Headers

[Anonymous]

Cool, I was looking for the formula Ben. Happen to know "A"?

[Anonymous]

Ok, I just calculated that formula.

A=3253
S=3.3122
D=3.622
d=1.2

This came out to 39.17" primaries. Sounds about right to me.

(Too bad the formula is from the 70s ) hehe

[SappySE107]

3252! holy crap thats a ton of duration for the exhaust!

[chevanater]

I have a machine shop hookup and the guy says he can make me headers for under $400. Any reason why he wouldnt be able to on my 96z?

[Anonymous]

Ok. Here is what i've come up with. I have a lightly modified Z34 running mid 14s. I talked to a few shops, as well as Headman Headers and Hooker Headers. Both gave me about the same measurments after taking my info. They said since i have a 5-speed, a low end is less crucial.

This is what we came up with:
1 5/8" primaries
36" long primaries
2 1/4" collectors
Run true duals with the mandrel bent 2 1/4" collectors

I asked how crucial it was for them to be equal lengh, and he said that it isn't a must, but he would recomend it, because it would be worth it. I plan on running the primaries side by side(to clear the ground), under the motor, and when my 36" is up, collect them. I'm hoping i can collect them up where i have the big hole (autos dont have the big hole) that way I clear. 1 5/8" is a lot less than 2 1/4".

So what do you think?

Also someone on the EFI boards said they can make the flanges easily, who was it? Because that is less work for me if so.

Also, how could i get the middle primary to match lengh with the outer 2 since i plan to bring the outer 2 together in the middle, but this would make the middle one shorter?

Do the primaries have to be mandrel bent?

[Streetrodder83]

Here is what I found out about the 75% Bias between the exhaust and intake. It's more of a range of 75% to 78%, well apparently this ratio does the best job of scavenging the cylinder. It's not much, but I guess that is the basic reasoning for it.

[SappySE107]

For what RPM is that the best for scavenging? How about powerband? There has to be more to it than 'this is what I say, so thats what it is". Thats the only explanation I ever get, and its just not good enough.

[Streetrodder83]

The exhaust is supposed to 75% of the intake, through the duration of valve lift. So whatever the intake flows at a certain valve lift it should flow 75% of that through the exhaust valve. This is for where ever peak torque rpm comes in for the engine, and with this percentage will continue to help make power past that rpm. If it's too low the exhaust ports would be the restricting factor in making power. To high a flow and you lose a lot off of the bottom end, but top end will improve. More or less I think it's to promote a flatter and broader torque band.

[SappySE107]

so blindly accept what you are saying cause you are repeating it? If you have a formula, dyno proof, respectable reference...anything, ill glady accept this. Until then, I can't believe it.

[Anonymous]

3252! holy crap thats a ton of duration for the exhaust!

I meant 253*. hehe


Aaron, yes, the primaries should be mandrel bent. I dont think you are going to want to run them under the car though.... have you measured ground clearance? Figure on losing 2" of it. For the tubes to line up, you'll have to have the middle cylinder primary bend a little back and forth to match the lengths of the outer primaries.


New question (for everyone): Does collector length matter? I plan on running the primaries into the collectors and then have the collectors meet and then split back out to the mufflers. Do the collectors have to be the same length when they meet up? Or will the equal-length at that point not be as big of a deal?

[SappySE107]

You will want the collectors to be the same length as well. After that point, I dont believe the tube length will matter as much.

[Streetrodder83]

I had heard this percentage from several people. But, I had an instructor at school give tell me this. Headerdesign.com also mentions it under engine consderations under the cylinder head heading. I was doing some reading, and came across two articles pertaining to cylinder head flow bench testing. You can find them at highperformancepontiac.com under the tech section. Here they mentioned the current trend is 80-85%, and there were tests that found to power loss at 60% due to combustion chamber design. Now, I know none of this is any better, because the article never goes any deeper into it other than mentiong those numbers. But, says that performance levels depend more on the cylinder head design itself, spark plug placement, valve angles, squish area etc. More or less it's points to ponder. There is a general header theory more or less a how things work, and construction articles at Burnsstainless.com . They are mostly advertising there computer software to design your headers. Now, I am thinking the best place to get information is some of the college auto engineering programs and see if I can find anything pertaing to cylinder heads and flow bias and talk to some local cylinder head shops. But, I am now finding out that it may not be as important as I once thought. I will admit that through more research that exhaust port flow doesn't have a great effect on header design. The only thing that I found mentioning anything on the flow aspect was at Burnd and that was that it is best to have a straight section or a radius slightly angled up. Having the radius angle down causes a disruption in port flow. They also recomend a book, "The Scientific Design of Exhaust and Intake Systems." Try and see if I can find it today.

[Anonymous]

You will want the collectors to be the same length as well. After that point, I dont believe the tube length will matter as much.

Hmm, that could be really tough to do. Especially when the front bank will collect around where the rear bank is just coming out of the cylinders! Have any ideas on how to get the two collectors anywhere near the same length? I have a picture in my head that shows the collectors about 3' apart.

[SappySE107]

I read that book already, but its kinda old and some of it doesn't match up with the newer info out today. Good read though.

I dunno about the collector placement, I was planning on running the rear bank differently than through the stock downpipe location. Automatics have more issues with that than manuals.

[Anonymous]

If I do this, I will definately do true 2.25" duals, mandrel bent, from the collectors back. I will probably have them both run in near the same location, maybe side-by-side, kind of like the new GTO. The rear set will be a little shorter, but it shouldn't matter, because it will be the 2 1/4" piping that is going all of the way out the back.