How much additional hp can I expect from a ghl cat-bypass exhaust? Will I get additional boost? I'm running 15 psi right now.

 

Do you have a cat back? The biggest gain is going to be spool. Boost will probably increase less than 1 psi and horsepower increase probably about 5 rwhp.

 

No, its a cat-bypass system. Starts from the down pipe. GHL is claiming like 20-30 extra HP. What is realistic?

 

That is on a stock car and the this will be less unless you have a catback as well. On a stock car just the pipe 10 or so whp.

 

Is it from the downpipe all the way to the rear of the car? including muffler?

 

Also depends on your cat and how it is. Mine was blocked bad so when I put in a 3" test pipe from Fabspeed I did see more power but at the same time 3 more PSI. After I turned the boost down to 15 PSI again I didn't see much more power but faster build up of boost though. The sound is awesome to!!