Other examples include a 350 cubic-inch (5.7-liter) engine with 400 horsepower, which would require a single pipe 4 inches in diameter, or with 350 horsepower, you would need a 3.5-inch pipe.

There are a number of formulas to help establish exhaust pipe size, but for an engine displacing 300 to 350 ci and producing 250 to 350 hp, 2-1/4 to 2-1/2-inch dual pipes work well.

PPA = (5,000 88,200) × 43.75 ci PPA = 2.48 Since header size is most commonly referred to with the diameter of the pipe there's more math to figure out what the area of a particular primary pipe ...

Typically, you'll see a 20 percent reduction in the inside diameter of a crimped pipe compared to a mandrel-bent pipe. "If you're mandrel-bending a 2.25-inch exhaust, it will flow as well as 2.5 ...

That's good news because it is easier to cut a hole for a smaller pipe. We decided on a piece of 1-1/2-inch exhaust tubing for the crossover pipe, which is roughly 70 percent of the main tubing size.