Quote:
Originally Posted by reeves
Biggest restriction is easily the cats. Replacing the stock header removes the cat, or replaces it with a hi-flo cat.. that's where I think people interpret as seeing the biggest gains in WHP.
Replace/remove the 2nd cat, and you'll remove additional restriction.. and get more WHP.
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Perrin saw almost no change by cutting out the front cat and replacing it with a straight pipe, this was with the rest of the exhaust already changed.
The fact that no amount of tuning with the stock header in place can get rid of the torque dip and the fact that most headers with a tune are able to almost eliminate, if not completely, the torque dip... I would say point to the stock header being the biggest bottleneck in bottom end torque.
Once you get into the upper rpm's you have to do the whole exhaust from the block back to get the biggest gains above 7,000 rpm.
Of course it's more complicated than replace this for that... the key is to maintain the highest velocity with the lowest back-pressure in the rpm range you want the biggest gain...
I think moving forward, you will see people doing the header before anything else, when they are after area under the curve anyway and not just sound.