header primary tube advice

What type of driving do you do? The only reason to go bigger would be if this is a full time track carl If it is a grocery getter/stoplight bandit/occasional bracket racer, you will be happier with the 1 3/4".

[email protected] said:

What type of driving do you do? The only reason to go bigger would be if this is a full time track carl If it is a grocery getter/stoplight bandit/occasional bracket racer, you will be happier with the 1 3/4".

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Amen to that. Even 1 5/8 might make a better curve below 4000 with little loss above 5000.

Willy, its a toy...... will be used on weekends and maybe once or twice a week. 3000 lbs prostreet nova.

xntrik said:

Amen to that. Even 1 5/8 might make a better curve below 4000 with little loss above 5000.

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I recind that.......

You have a heck of a cam...... go 1 3/4 if you were satisfied with their performance.. 1 7/8 might lose a little down low and pump you up above 6000.

One of the largest errors street enthusiasts make is in running too large of a primary pipe, and too large of a collector. For example, NHRA and IHRA Stock teams using Burns' headers in H/SA in traditional small-block powered musclecars are running 1.5-inch diameter primary pipes- much smaller than many street machines are trying to use.
"The purpose and rpm range of the engine determine the primary pipe length, while pipe diameter is governed by engine displacement, valve diameter, and valve curtain area (determined by camshaft dimensions).

http://www.popularhotrodding.com/tech/0310phr_jack_burns_exhaust_manifold_header_tech/

How long are your primary tubes?

novakind, primarys are 32" with 3" exhaust (with x pipe) all the way back...... i dont know if im gonna use or should use the x pipe, the car has been freshly backhalved and i may just dump the exhaust before the tires......

What are your goals with the exhaust system? Maximum power, power in the range you drive in, sound, looks, convenience, cost, etc?

My goals are to somehow get the exhaust up closer to the body of the car inside the frame rails so that when i go over speed bumps and high spots in the road i dont cringe and hear that lovely crunching sound as my headers get smashed (supercomps go 3" past the frame on my nova and a lowered car doesnt help)...... I realize this means custom headers and have been looking into the weld up headers offered by hooker and hedman.
Seeing how my car is gonna be mostly a street car with the occasional romp at the strip I still want performance and functionality but with the above mentioned criteria and with the weld up kits I think I can do it. Also, I do have to say that with its current setup the car has monster torque and I dont wanna give up too much of that, but a little is alright.

I found this article to be helpful : http://www.superchevy.com/technical/engines_drivetrain/exhaust/0505phr_exh/

Do a search on header design. There is a whole lot of good reading material on that subject here.

If it makes under 500hp and has to leave a traffic light with a cop car behind it then 1 3/4 should be plenty . Most Nascar small blocks in the late 70s ran 1 7/8 but they rarely ran below 5 grand.
My body off HQ Holden ute has a 400sbc with 220 cc intakes and 1 3/4 primary. It's a long way off but a friend with a 10 sec 2800lb HR Holden ran 1 3/4 then switched to 1 7/8. It went 10.54 @ 131 before and 10.81 @ 128 after - 355ci, 4500/glide, 28 inch M&H w 4.10 gear.

yeah, ive been reading alot about it..... I thought it was interesting that the primarys dont all have to be the same length. You should be able to have minimal power loss with an 8-9 inch difference in primary length, which would lessen the pain of header making a little. Whether thats true or not, I dont know.

i also find it interesting that they don't have to be the same length.

anyone care to elaborate ?

Again, do a search on this topic. Primary tube length MUST be the same length and that length MUST be tuned to the rpm where you want max power. Unequal lengths will have different cylinders peaking at different times in the rpm range. I did my senior project @ Fresno State on exhaust and intake design and the theory holds true. A few inches difference in pipe length has measurable impact on HP.

By the time you get to that stage where pipe lenght makes a difference your not building your own engines anymore.

For a street car, the idea is worth noting but you won't be in any kind of tuned RPM range for long enough to worry about it. That time spent is better off maximizing the combo you do have.


I think 1 3/4 is way big. I use that size on comp engines make twice the power. I'd stick with 1 5/8 max.

As with all engine decisions, it's a compromise. If you want some performance, design them by the science. If all you want is bling bling and getting the exhaust to the rear of the car as is the case in 99.99% of the street rods out there these days, stuff them in the easiest way.