At what poing are 1 3/4" pacesetter longtube headers a "restriction" and how much would you benefit from changeing to something like kooks 1 3/4" to 1 7/8" stepped headers?

 

Im not pro but I would say Longtubes would be good for at least 550 hp.

 

With your mods that you have now, they will be more then adequate. When you start pushing big numbers from a well built motor, then I could see the benefit of stepping up to larger size long tubes.

 

It has to do with were you want to make power. The bigger tubes are a match for more inches or higher RPM performance. You can kill midrange power and torque with to big a primary tube header.

 

A buddy of mine pushed 1,125 flywheel HP through a set of 1-3/4" Hooker LT's, with a Borla XR-1 muffler hanging on each collector. If you want to push more than that through a set of LT's, consider the larger diameter Kooks.

 

On the other end of the stick, are too large of a header ever going to actaully cost you power do to lack of back pressure?

 

Its not an issue of "backpressure".... everybody has to wipe that word out of their exhaust dictionary. Large diameter primaries hurt you at low RPM, because the gas velocity drops. That eliminates scavenging, and you get less A/F charge in the combustion chamber. Allow the primary velocity to go too low, and you'll get exhaust gas reversion into the heads. "Stepped" headers are an attempt to keep primary velocity high, at least for the first few inches, so that scavenging is maintained. But, that smaller diameter section hurts you at high RPM where it restricts flow due to excessive pressure drop.

 

Short answer - NO .

Long answer - see Injuneer's post .

The bigger tubes will only moderately impact low end torque. Beyond that, the sky is the limit ... you can't get "hurt" by an exhaust that flows "too much" . BUT, there are applications where sacrificing the lower end torque for high end gains may not be worthwhile, and the opposite scenario may actually be the best .