Be Careful What You Pay For !

When you go to a muffler shop to have a high performance exhaust system installed you have to be careful about what you are getting for your money.  A perfect example of that is the 1988-2001+ GMC and Chevy full size trucks.

Some muffler shops will suggest to you that your stock tubing is 2 3/4" in size, and that by increasing the size to 3" will give you better performance.  The problem is unless your tubing is mandrel bent you are not going to gain any performance because of the method used to bend the pipe.

The stock pipe in figure A measures 21/2" at the center of the bend.  Because muffler shops use a press bender the pipe actually smashes harder at the center of the bend than the stock pipe.  Although the muffler shop is selling you larger 3" tubing, as you can see in figure B the center of the bend measures 21/2", the same as the stock tubing.

Because both pipes have 21/2" restriction at the bends, you are not going to gain any performance with the 3" tubing unless it is mandrel bent.  With the mandrel bending you are getting true 3".  That will give you 35% better flow, and increased horsepower, torque, and better gas mileage.