Tom W

The 964 isn't too different than the 993 so I though I'd post my results here too. There's lots of talk about how restrictive 964/993 exhaust are and how much hp can be gained from exhaust changes. I decided to test the claims with the dyno. The 964 set-up is a bit different in that the headers are more convoluted (nowhere near equal length) and the mufflers run in series instead of parallel. So in the 964 the exhaust is header to cat to primary muffler to secondary muffler and a single outlet while the 993 sequence is header to cat to muffler (with two mufflers and outlets). The secondary bypass simply removes the muffler in favor of a J-shaped pipe.

Stock headers, cat, primary, secondary bypass: 230 rwhp
Stock headers, fabspeed cat bypass, primary, secondary bypass: 244 rwhp
Fabspeed equal length headers (no heat exchangers), fabspeed muffler: 239 rwhp

At tests on the same dyno with very similar weather (temp and humidity).

So, now that I've passed my semi-annual smog test, the cat comes back off and I add the cat bypass back. Headers and Muffler have been returned to Fabspeed. The added benefit of this configuration is it easily passes sound requirements at Laguna Seca (at 89 db) while the fancy headers and muffler were way too loud (96 db).

Pete Lech

Interesting test. Seems that the factory headers make more HP than the fabspeed units.Thanks for sharing.

My understanding while that the 964 exhaust system was very restrictive, like the post-75 Carreras, but the 993 exhaust system was vastly improved.

Would be interested in seeing a back-toback comparison on a 993.

Jean

Tom,

Thanks for the information provided. This should open up the eyes of many who are thinking of spending money on exhaust systems.

The one thing dyno will not show however is the throttle response. In a turbo engine, the improvement of a cat-bypass system on boost lag and throttle response is very considerable, I guess on N/A cars it should be quite noticeable as well, albeit not as much.

Kevin has always said that the fatory headers modified, polished ported etc.. will yield great results, I guess this confirms it.

The equal length headers do not give you more hp, they just provide better throttle response at high end RPMs

Thanks

Christer

IMHO that statement is completely wrong. I use a 964 system with catbypass and cup pipe and have around 315rwhp. Of course the car is far from standard but the system is able to flow quite well.

Christer

p.s. I used to have a GHL exhaust which added around 23fwhp and 20lb/ft torque to my then standard car. This was without any chip change or other mods. This was dyno verified at the time by a UK independent who were as surprised as I was...

Steve Weiner-Rennsport Systems

Good post, Tom.

I'd just add that several years ago, we ran a stock, chipped '93 RSA race car on a DynoJet testing several headers (using our Flowmaster Series 80 race muffler for each run): B&B early & late, GHL, and George's headers. All headers had the same diameter tubes.

The differences were rather surprising and each header made an even bigger difference than what you observed. My conclusion was that they were VERY worthwhile for maximum torque & HP as long as one had the ability to optimize the A/F ratio for each application. I diod not test any Fabiani product.

My point here is only that headers are NOT all the same and some work better than others.