Yea, this is my next mod...i need to get rid of my boost stacking....the 3.2 pulley is killing me.

Since the headers are lowering boost, is that going to hurt low-end performance?

At the same time I'm going from a 3.8" pulley to a 3.3" so I hope to gain boost. 11-12psi is my target.

The same amount of air is forced into the engine. The engine just breathes, and exhausts better so the amount of pressure in the manifold will be less showing as less boost on the gauge. It will still make more power with smaller pulleys though.

I saw 11 with my 3.2 pulley on the dyno. With headers I would expect this to drop to 9 or 10. My guess is with your 3.3 you will see about 9 - 9.5 with your headers on.

However, your going to gain about 20HP with the headers, and probably 25 or so with the pulley. A 45HP gain you are REALLy going to notice. I thought 25HP was a big gain. Just wait till you drive this when your done! heh....

Because it breathes better, will it help milage as well?

I believe the answer to this is yes. I have found thought that gunning it is so much fun now that im into the throttle a whole lot more now, so im actually reducing my mpg. But driven normally this should be true.

Yes. It should raise freeway gas mileage 1-2mpg.

As was already said, the engine will be flowing the same amount of air, so it will still make the same power, but actually the low end torque will probably be increased. On a completely stock GTP (completely stock engine, and completely stock exhaust) by installing only TOG headers it gained 18hp and 16ft.lbs. at the wheels. So, the torque should be increased with the headers. Plus they give you the ability to run a smaller pulley, so you can add 30+ horsepower with just headers.

An L67 with the stock M90 blower will handle ~11-12psi boost without an intercooler without getting KR. So when you do an exhaust mod that lowers the boost, you want to raise the boost back up to the same amount of boost as you had before the exhaust mod. On your own car you will find the level where it starts to get KR, so when you go to a smaller pulley, you just need to make sure that you are running the same amount of boost as you were before the exhaust/valvetrain modification, but generally it is 11-12psi.

Shawn

Wow, I really want some headers now.

I was going to put them in this weekend but I have a bad cold right now and not sure if I'll be up to it. Call me silly but I dont want to slug through this install and just get it done, I want to enjoy it and take it all in. I hope I feel better by saturday :(