[vin63]

Originally Posted by SactoJim

...Right now I'm running a set of Doug Thorley tri-y headers (5/8" primarys/2.5" collectors) that I've had for a long time, fit very well, good ground clearance, and have never given me a problem....nicely made header. My main question is if I'm giving up much hp with these and is it worth spending the money for some 3/4" primary headers or not?....and if so, the challenge is finding some that fit well and give me decent ground clearance. Current exhaust is 2.5" all the way back with an H pipe.

Thanks....Jim

I'm assuming you mean 1.625 primaries, which is plenty (I'm currently making 528 bhp @ 5200 RPM with 1.625 primary headers). If there is any restriction it would be the H-pipe. I tried just about every combination of headers on my Super Gas car over a period of 20+ years (650+ bhp @ 7900 RPM). The only improvement I found was a 2-3% increase from a 1.750 to a 2.00 primary (same configured headers) at the 7600-7800 RPM range where the exhaust velocity could take advantage of the larger area...but, I lost about 2% torque at the lower RPMs, so it was a push for me. Unless you plan on/presently operating your engine at WOT frequently, you'll probably not realize any improvement. I would use the money someplace else.