Glad to see that some numbers have finally entered the discussion along with the reality that if the exhaust system ( pipes, bends, mufflers ) are causing a significant flow restriction, then what type a header you put on won't cure it, and may only make it worse. As in everything else in a car engine, all the parts have to be matched to work together properly. Buy a high performance header and and attach it to a stock exhaust system and the result will probably be less power than stock, particualarly in the low RPM range, not because headers always cause a loss of low end power ( we can show the opposite on the dyno ), but because the header is not a match to the rest of the system. Tried to post a comparison photo of
our 2.5 inch tube used in our performance exhausts compared to stock but had a problem uploading it. Will try again later when I have more time.

Unless I missed it, its surprising that dimensions of exhaust pipe have been mentioned, but not one mention of the header dimensions - diameter of primaries, secondaries, collector, lengths of primary, secondary, etc. All of this makes a tremendous difference. We have been offering 3 different sizes of 4 - 2 - 1 headers in order to match the needs of B18/B20 engines from 1800cc stock to 2200cc highly modified. The idea is that a header that will work on one application will not work on another. In general terms, what will help a 100 HP B18 won't help a 160 HP B20, not to mention a 220 HP supercharged engine.
We also offer several different 4 - 1 designs, but the 4 - 2 - 1 type is clearly better for street applications where a broad power band is clearly more important than peak HP.

Looking at the photo of the header mentioned by Per from Kirk Racing, I'm willing to bet anyone $100 that they have no dyno testing to support their design. What is clear from looking at the photo, is that the goal was price, not a performance improvement over stock. It looks a lot like the 4 - 1 design that J.C Whitney used to sell for $50. That's not to say that matched to a properly setup exhaust system it might not show an improvement on someone's engine, especially if it replaces a single down pipe, 1.5 inch design with a better flowing system, but its extremely doubtfull that it will show any improvement over the stock cast dual downpipe design of the later B20s, when matched to similar exhaust systems. Hopefully per will do a dyno comparison so that we will know. I have also offered to send him one of our headers to use in a comparison, as he did on the 122 project car several years ago.

If I can work through some glitches in a new program I am using I will post some comparison photos late tonight.


John
v-performance.com