I have been playing around with the header primary tube diameter formula and wondered how small in diameter I could go before I reached the diminishing returns in low end torque gains.
With a 359W, .040" over 351W:
.040" thick wall tubing
-1.5" O.D. primary tube, the peak torque is 3,105 rpm.
-1.625" O.D. peak torque at 3,707 rpm.
-1.25" O.D. tube the peak torque is 2,112 rpm.
-1.375" O.D. tube the peak torque is 2,594 rpm.

Can I really go down to 1-1/4" or 1-3/8" O.D. and expect to gain any low end torque over a 1-1/2" primary tube header?




This is where my engine is. I swapped my camshaft and lifters for a hydraulic roller setup. I got the Schneider 266-78RH. The cylinder heads and intake manifold have been ported.

 

How are you calculating those torque numbers?

 

peak torque rpm = primary pipe area X 88,200/ displacement of one cylinder

 

Ahh OK. What are your predictions for HP and TQ peaks from the motor? The exhaust system can massage those numbers up or down in RPM a little but it won't totally change them so the exhaust system should be sized to work with it as much as possible.

 

Came across this article few years ago and can not recall if the info would apply, or be of any help?????

Header Basics - How Headers Contribute to Horsepower - Car Craft Magazine

 

I don't have any predictions yet.I want as much torque right off idle around 500 to 1,000 rpm as I can get and secondly I want to stretch that torque curve out as far as I can get while retaining a flat torque curve.

I have the Schneider 266-78RH.


I really want to build the middle/peak torque to its max and balance the low-end and top-end torque.