What's the difference between the Saab sport exhaust and the stock exhaust on a 900SET?
Is it only a free flowing muffler and the lack of of a resonator, or is the pipe bigger?

To get some extra bhp I want to install a 3" downpipe and a racecat. The rest of the exhaust is stock, no resonator and the rear muffler is replaced by a free flowing unit. Does it make sense to replace the complete exhaust system?

Your are correct about the Saab Sport Exhaust, and it is the same diameter as the stock system. Do not think about it in terms of horsepower though. I have a 3" downpipe, high flow cat and the Saab Sport exhaust on my 1996 900SE. It probably gives me an extra 15-20 HP extra by itself. The real purpose of it is to decrease the turbo backpressure and allow for much quicker spool up. I can reach max boost by 2500 RPM and sustain it for longer. So a freer exhaust will not do much for horsepower but it will help your accelerations a great deal. Once you have a free exhaust you can increase boost pressure and gain considerably more horsepower. Check out my website, it has some good info.

http://www.lehigh.edu/~erp4/Saab.html

Eric

http://www.lehigh.edu/~erp4/saab/Upgrades/MaxBoost.JPG

Eric, thanks for the info!

Your website has been very helpfull finding info about mods I've done and mods I'm going to do.