Originally Posted by Gunter (Post 4290632)

SSI's would balance better but you would probably not notice much improvement unless you go straight out with a 2in/2out muffler but.......................
All 2in/2out mufflers have a very bad drone/resonnance between 2-3k that will drive you nuts.

I've tried M&K, Dansk etc..............and it's just disgusting.

2in/2out are great for the track but not for street-driving.

With 9.8 CR, concentrate on mixture, timing and octane to prevent detonation!
What is the curve on your distributor?
Is it a Bosch 0 237 306 001 or 0 237 301 007 or 0 237 301 009 ??
What plugs are you using?
Bosch ???

Originally Posted by autobonrun (Post 4291467)

First, the HP improvement from the "free flow" exhaust is questionable as far as I'm concerned. The real improvement comes from the balanced SSI's.

You want hard proof. There's a related thread on the site right now. In it I linked to an old thread I posted several years back. I actually ran some before and after tests using a G-tech pro. The results are shown. They were not scientific and I didn't spend thousands of dollars insuring that all the parameters were equal but I did try to keep the before and after tests as consistent as possible. I also used a sound meter and recorded the difference in dB levels if that is of any interest.

Also, I had two dyno tests done right after I installed the SSI's. The results were within 1 HP of each other as far as peak HP. Let's just say the car dyno'd with more HP at the rear wheels than Porsche publishes as the stock crank HP. So yes, I got at least 15 HP improvement. But as others have said the butt-o-meter also reflects the improvement.

http://forums.pelicanparts.com/porsche-911-technical-forum/394868-performance-upgrades-911sc-3-0-a.html