Exhaust backpressure the myth - ThumperTalk



- It's about velocity (like a couple others said). You want as little backpressure as possible while maintaining the appropriate velocity to compliment your desired powerband. A large exhaust volume (such as a race engine screaming at 8-9k) automatically creates a high velocity, so people use open headers to improve their peak numbers in those higher RPMs. Is the velocity killed in the lower RPMs, where a street car would normally operate? -yes. Do they care? -no.

-You see all the time where just adding longtubes decreases low RPM torque but vastly increases top end HP. It's all a give and take. A great example in the article above is how Ferrari uses dual exhaust paths to promote higher velocity at lower RPM but less backpressure at high RPM. Vettes and other cars are starting to do this as well.

Everywhere you look, manufacturers are using technology to improve/modify flow velocity of their air pumps (engines). I first noticed this in the FR500 magnesium intake that had butterflys that opened and closed at specific RPMS - optimizing air velocity entering the engine by mechanically lengthening and shortening the intake runners. The same thing is achieved by variable cam timing (which is showing up in pretty much everything now).

So, to answer your question - put some mufflers on the damn thing - I don't want your 200hp car to blow out my ear drums when it goes by. A reasonable 2.5" exhaust system is fine for most cars out there. Will you extract that extra 5-6 hp? -maybe, maybe not, but trust me, the money is better in your pocket.