Re: 4bbl or 2bbl
Real question for anyone who's run a car with and without headers: Do they add any power?
In my (very brief) experience doing PR for an exhaust company, it seemed like any gains you would actually make were (A) excruciatingly small and (B) usually near the top of the rev range. In other words, the power gains would be mostly theoretical for how most teams run their Lemons engines (Unless you have that one guy who always wrings the engine out to factory redline to make the pass at the end of the straight). The marketing people could still say "Adds up to 10 HP" because while a B18A1 will indeed breathe better at 6600 RPM, if your drivers are revving the aforementioned B18A1 to 6600 RPM every shift, it's not going to make 10 (or 3 or whatever) more ponies for very long.
I realize that isn't categorical and that some exhaust manifolds are SUPER restrictive, but it always seemed silly to think that it was the one thing that was holding you back. Mostly, they just seem to make the car sound a little better and much louder, which is extremely unfun if you're driving a race car for over an hour.
Have you seen explorer 5.0 exhaust manifolds?