Many advertised products fill the pages of this magazine. Many of them work well,but some of them do not.
For example, I've seen many cat-backs that are noisier and make less power than stock ones. A poorly designed, overly restrictive exhaust effects pretty much every other performance part you add to an engine. So, the question is, how do you know before you buy?
When tuning a Civic Type R in England with Toda cams and a Toda header, I started off with a program I developed for an RSX with identical cams and Toda headers using a Brand X exhaust. This Type R, however, lost 25 lb-ft of torque immediately after the 4,000 VTEC crossover point, and no amount of tuning could fix it. So I consulted my proctology notes, extracted the dyno's tailpipe O2 sensor, and took a look. What I saw was a great example of how not-to build a rear muffler. The internal diameter of the rear muffler was only about 1.5 square inches. A quick swap to a spare cat-back immediately recovered our lost 25 lb-ft of midrange torque and added 20 peak horsepower to boot.
So next time you're shopping for a cat-back, take a look past the 10-square-inch tip and look deep into the internal section. If you see a pipe significantly smaller than the entry pipe, you are very likely to lose power.-Doug Macmillan of Hondata