I want to be clear, I agree that bigger pipes will likely lead to more HP, but tend to shift the powerband toward the upper rpm range as I experienced.
My goal was to maintain the low end that is so much more usable on the street, and this is where the difference between torque and hp becomes meaningful. Given the desire to have the low end at the sacrifice of top end power, the slight restriction or build-up of back pressure from smaller pipes has a positive effect on low end power.
Knowing that torque is also the byproduct of mass and knetic energy, that means that the slower, lower rpm crankshaft is not totally responsible for the high torque in a L98 engine.It cannot be at slow speed, only higher rpm where it merges with raw hp that can maintain the load against it.
The generation of torque
has to be assisted by some mild back pressure. Sure, this has a top end liability, but again, big top end pulling power is nice but its simply not practical in a street beast. Thats why I have 3" up front (to help scavenge the cyl) with the drop to 2.5" at the rear Y into the muffs.
NOTE from the LINK: interesting read... I brought a paragraph that supports what I've been saying...please read !
Headers -- Primary Pipe Diameters
Big pipes flow more, so is bigger better? Answer: absolutely not. Primary pipes that are too big defeat our quest for the all-important velocity-enhanced scavenging effect. Without knowledge to the contrary, the biggest fear is that the selected tube diameters could be too small, thereby constricting flow and dropping power. Sure, if they are way under what is needed, lack of flow will cause power to suffer. In practice though it is better, especially for a street-driven machine, to have pipes a little too small rather than a little too big. If the pipes are too large a fair chunk of
torque can be lost without actually gaining much in the way of top-end power.
At this point determining primary tube diameters is starting to look like a tight wire