Who needs a size chart? The bigger the pipe the more the powaaahhh, right? Well, up to a certain point. So if you’re getting ready to install a new system that’s as wide as a Brontosaurus’ tail, you may want to hold up a sec.

The best size for your application depends on both engine output and displacement. As a general rule the higher each of these components, the larger the pipes should be. Larger diameter pipes reduce backpressure by allowing more exhaust gas to exit so your engine can breathe more efficiently, giving you more output and better fuel economy. But there comes a point where you begin to create too much room in the pipes and the exhaust gases cool and slow down during their travel.

The goal is to improve exhaust flow and to reduce additional backpressure, so just changing the OEM exhaust tubing with mandrel-bent tubing of the same size or one size up from the OEM will do the job in most cases. As a general rule, you can enlarge the pipe diameter of your OEM exhaust system by 1/4 to 1/2-inch to increase your horsepower. But going any larger is likely to decrease your performance; specifically, low end torque.

Engine Size	Horsepower	Exhaust Diameter
		Single Exhaust	Dual Exhaust
150-200 CID	100 to 150	2″ to 2-1/4″	2″
200-250 CID	100 to 200	2-1/4″ to 2-1/2″	2″ to 2-1/4″
250-300 CID	150 to 250	2-1/2″ to 3″	2″ to 2-1/2″
300-350 CID	200 to 350	2-1/2″ to 3″	2-1/4″ to 2-1/2″
350-400 CID	250 to 550	3″ to 4″	2-1/2″ to 3″