Header size for high hp whipple cobra

[RoadRash]

I don't think you will gain much by going to a 3" system. Headers arn't much of an improvement over the stock logs until 600 hp or higher. At your power level expect to see about a 10 hp gain. The big exhaust will drone due to the lower resonance frequency and a small loss of low end response. If you were racing and kept the engine above 6000 rpm then the larger tubes would make more sense.

Personally I won’t run LT's due to scraping, leaking, makes it harder to work on and won't pass emissions :cuss: I have JBA shorties with 1 5/8 primaries which will reduce some of the pumping losses in the engine, can fit many combination's of off-the-shelf exhaust systems and will pass emissions. 2 1/2" front to back will maintain higher exhaust velocity and purge the system better and low to moderate rpm's.

Good info .. My car is definitely a street car and no emissions to worry about in VA. and not much if any track time. I would really rather keep my 2.5" Bassani catback .. as it is fairly new.

So, what primary size? Looks like 1 5/8" is popular with guys at similar power levels. Should I do stepped with that as well? 1 3/4" to 1 5/8" (EDIT: I meant 1 5/8 to 1 3/4's)?

How about collector? 3" or 2.5" and just run 2.5" all the way back?

 

[98 Saleen Cobra]

Do the 17/8'' primary, it's just the way to go on high hp applications.. Talk to Griggs racing and ask them about the 660rwhp 98 Cobra they run. They run 17/8'' primarys. Me personally i'm running 1 3/4'' because I didn't think it through all the way.. And yes run a full 3'' exhaust. You won't notice any low end tq being gone.. I run a full 3'' and it's perfect. My tq is still high as hell and my hp went up as well. Also call Kooks and see what they recommend.. Also something to think about the Cobra Jet from ford runs bigger primaries for a reason, and any road racer or big hp drag racers do it for a reason.. Just saying bud..

 

[TORQJNKY]

I'm running Kooks 1 3/4" to 3" collector to catted x-pipe with 3" inlet to 2.5 magnaflow catback. A 3" collector gives you the option to go to a 3" exhaust if you ever decide to in the future. Mine headers are just over a year old. The only thing I am not crazy about is the slip fit tube on each side and the headers hang pretty low. I also had a slight vibration issue with where the header came into contact with both my stock and aftermarket K-Member (PSR). Little heat and a crow bar fixed that. The slip tube makes the install much easier but will sometimes leak. If I had to do it all over, I would go with ARH.