i've currently got some custom made 4-2-1 headers... i know they aren't anything special. maybe a tad better than the stock setup.
i have a friend selling some tuned length race headers from an ITR... they managed a dyno proven 9hp increase. they are kinda pricey....

do headers really make much difference to the overall performance of the exhaust system??

btw... i currently have a high flow cat and 2.25" mandrel bent system going into a 2.5" muffler.

 

I header will make a difference in your power curve. It allows higher flow of your exhaust. If may also make your exhaust louder.

 

A decent header definately makes a difference. A 9HP increase isn't all that special though. Here's a link to the most exhaustive evaluation I've seen on the subject. Note the range of gains was 9-14 peak WHP. Hence a gain of 9 from a pricey piece just doesn't seem worth it.

http://www.automotiveperformanceengi...om/header.html

 

nice numbers on that header test...

 

Headers for me a on pretty much stock car made a huge difference! If you do on plan getting a "race" header you probably won't use a cat, if you do use a cat/test pipe plan on changing your cat/test pipe because the length for ITR's and GSR's are different.

 

I have a '94 GSR with headers and a short AEM air intake and my headers are 4-1 DC Sport headers and top end they make a big difference. They will make your exaust flow better which will make it louder. Mine add about 13 horsepower.

 

Your headerS only add that much because you have so many of them on your car.