Originally Posted by msheredy
That's assuming you install a set of headers with primaries that are too large. A properly designed header will always out perform an OEM manifold no matter what you are going after, 0-60, top speed etc.
Not really plenty of headers that are available will actually reduce 0-60's. Headers on stock vehicles show small gains and hardly justify the cost. If you are doing it because you have several other mods like ported heads bigger turbos.... then headers are worth it if you are looking for every last drop of horsepower. Dynos on FJ cruisers, Vipers... that the only upgrade is a set of headers will net you about 15hp and that's about 500rpm before redline. I owned alot of cars and all were modded by me from ported polished and decked to full out strokers and you will be dissappointed if you believe the claims that header company's make.
A good example is Diamond eye down pipes for diesel trucks. They claim faster spooling and more power they do make more power but at redline not really much of a point to that because you ain't holding reline very long unless your sled pulling and even then, not real long.