[Rick]

First Mike made it hard to add to the thread, then Mici has to beat me... Nice posts, guys. I think all I can contribute is turbo sizing choices.

For a setup only hitting a max of 9 psi, you're going to want a really small turbo. I'd look for a 14b out of a 1g 5-speed DSM, or a T25 out of a 2g DSM, or even a 13b out of an automatic 1g DSM. You may ask "Why does it have to be out of a DSM?" or "Why are you pushing DSM turbos when there are so many others to choose from?" Well, it's because DSMs are probably the most common turbocharged non-deisel cars in the United States, so you've got a lot of junkyard choises. Any small turbo will work.

The problem with larger turbos is that they give a lot of turbo lag - lots of hesitation in the low rpm while the exhaust pushes the turbine, trying to spool it. The bigger the turbo, generally, the more lag it will have. When you've got a huge turbo, it will take anywhere from 3500 to 5500 to spool, making it a pain in the butt to drive in city traffic. My HRC Super 20G, for example, hits full boost (23 psi, last time it ran) at about 3700 rpm, and my Talon is about as slow as my Tempo before it happens.

The problem with small turbos is that they get overrun quickly. On my 2.0L Talon, the 14b hit full boost at about 2500 rpm. On a 2.5L 6, it should be even quicker. However, on my Talon, that turbo starts to run out of air around 6k, and the car just about shut down after 6500. This can be fixed by porting and clipping. Porting, obviously, allows the turbo to flow more, so it isn't as much of a restriction. Clipping involves actually cutting off parts of the fins of the turbine (exhaust fan), which makes it spool slower but hold boost much longer. I've always recommended going this route when turboing a 6, and I always will.