Originally Posted by msheredy
Nobody needs headers. People want them to increase performance. Will they free up horsepower and torque? Of course they will. When was the last time you saw/read about a header swap that didn't end up increasing both horsepower and torque?
It was on a Lexus 3.0L inline6 IS300. I believe the company was Skunk racing, or was it Skunkworks racing? Anyways they built up a full set of headers for this car, and it didn't make any more hp then it did in stock trim. The restriction wasn't the manifolds it was the exhaust valve ports.
I've also seen a guy bolt on a larger throttle valve body on a 4 valve dirtbike. No horsepower was gain from this because again the restriction was the intake valve ports.