Title:Measuring Backpressure

Since horsepower is derived from burning fuel, the more fuel the engine efficiently burns the more hp (and exhaust) it will produce. Each engine mod that improves hp WILL increase backpressure. A 40% increase in power will typically double backpressure.

How To Test Your Current Backpressure

ALL that is needed is a pressure gauge, a few fittings and some tubing. Locate a pressure gauge that will measure up to 10 psi (a large dial makes for easy reading.) Weld a "tap" into the exhaust system before the muffler and (if you have a cat) before the cat.

The tap can be as simple as a hex nut drilled and threaded for 1/8 or 1/4 inch pipe. Drill a small hole through a pipe plug (the pipe plug must be the same size as the hex nut thread) and braze a 12-18 inch length of 1/8 inch steel tubing (available as brake line in auto stores) to the drilled hole, the steel tubing will dissipate enough heat so you can attach the rubber hose of the pressure gauge. Be careful to route the hose away from the other exhaust system components. After the pressure measurements are complete you can remove the tubing and block off the system taps with common (un-drilled) pipe plugs.

Backpressure is measured by accelerating the car at WOT and at regular rpm increments noting the pressure on the gauge. ANY backpressure is undesirable but it is not possible to achieve zero restriction you have to have a REALISTIC goal.

Stock exhaust systems are about 8 psi, some are 9 psi. With better mufflers, catalytic converters and tailpipes IT IS possible to get as low as 2 psi. If the measurements indicate a backpressure of more than 5 PSI during full throttle operation at any point the exhaust system needs work.

Written By: yt500pmd
Edited By: betterthanyou & AciDBatH666