From: Jim Bailey [jim@928intl.com] Sent: Thursday, October 24, 2002 5:36 PM To: 928 Subject: [928] Re: 928 developments Not intended to pour fuel on this fire but the 89 GT which Ron G. who works here "races" ( trailered none street car 2950 lbs ) when he removed the cat convertor two resonators and RMB , he installed a custom " X "pipe two magnaflows in front of the rear axle and dual 2 3/4 (or 3 inch inch pipes) using stock exhaust manifolds ....he got a 29.5 HP increase same dynojet two days apart , right at 300 HP at the wheels , everything else is stock . Correct , stock exhaust manifolds 29.5 HP increase by eliminating the cat convertor and stock mufflers . I do NOT sell these .... Jim Bailey 928 International Jim@928intl.com www.928intl.com (714)632-9288 From: louisott@cs.com [mailto:louisott@cs.com] Sent: Saturday, October 26, 2002 4:55 AM To: 928 Subject: [928] Re: 928 developments Hi Walt, I have done testing as you describe. My results weren't as successful as yours, but close. This particular batch of tests was done at the Mustang dyno shop in San Jose using my '90 GT. The first series was to check the effectiveness of various cat "test" pipes as compared to the stock cats. No exhaust system was connected after the cats, or cat test pipe. A cat test pipe of 2.25" OD (about the same ID as stock 928 pipe) with an "H" crossover gained 20hp over the stock cats. A cat test pipe of 2.5" OD with X crossover gained 30 hp. Stock Porsche cat section with the cats cut off and replaced with 2.25" pipe gave a 20hp increase, same as the "H" cat test pipe. That series of tests was terminated when we were run out of the dyno shop because the owner thought the car was too loud doing the tests with no exhaust other than the cat test pipes. Weenie.... Back home I continued at the local dynojet shop where a nice sounding 4 cam V8 is appreciated. I tested Tom Cloutier's "V" merge collector in 2.25" and 2.5" size as compared to my 2.5" X crossover (30 hp gain over stock cats). Tom's 2.5" OD merge collector was the same power as the X crossover. The 2.25" OD merge collector was off on power, but I don't know by how much without going back through the dyno charts. Point is that the 2.5" OD made more power throughout the rpm range than the 2.25" OD size. Both the 2 into 1 "V" merge, and the X was equivalent. These tests were all done without rear exhaust or mufflers, and all the pipes were very close to the same overall length. All were connected to the stock exhaust manifolds. No headers. After seeing what worked up front, I tried different rear exhaust pipe and muffler configurations. To Tom's merge collector which has a 3.5" OD outlet, I connected a 3.5" pipe with a single straight through muffler leading out to the rear of the car. The result showed no power difference, throughout the 2500 - 6400 rpm range, whether the tailpipe and muffler was connected or not. Next, I used my X crossover and the dual 2.5" OD tailpipes and two 4"x8"x16" straight through mufflers. Again, there was no difference in top end power, but the dual pipe setup showed a slight bit (about 5 lb ft) more torque in the 4000 - 5000 rpm range than without the tailpipe & mufflers. All these tests were done on the same day. I have also tested this system with aftermarket cats and see about a 6 hp loss over no cats (different day test). So what's the conclusion? Without headers, and without cats, you can get a 30 hp gain if you use either a 2.5"OD X crossover or a 2.5" OD 2 into 1 "V" merge collector and appropriate tailpipe and mufflers for either. Add cats and subtract about 6 hp. You won't see the full 30 hp gain if the stock tailpipes and mufflers are retained. It'll be a bit less. I've seen around 15hp gain on an automatic. I have not seen 15 - 20 hp gain with the Dastek. More like 12hp, but that could differ a lot with different engines. I haven't experimented with headers. One thing I have noticed is that they give more torque up to 4500 rpm or so and that can make a lot of improvement in everyday driving response. Louie Ott '90 GT currently without a heart. From: LouisOtt@cs.com [mailto:LouisOtt@cs.com] Sent: Saturday, October 26, 2002 1:54 PM To: 928 Subject: [928] Exhaust info clarification Hi All, Last night I responded to a message from Walt K. with information on some exhaust testing I had done. While I have not done testing myself with headers, I did make a comment regarding headers. The comment was this, "I haven't experimented with headers. One thing I have noticed is that they give more torque up to 4500 rpm or so and that can make a lot of improvement in everyday driving response." I should have added a bit more to that I think. There is at least 3 different headers designs available, maybe more. We have the MSDS, Devek, and Tom's crossover design snake pit headers. I don't know much about the MSDS so I'd better not say anything regarding those. Devek's latest header design is excellent in producing more top end, mid range, and torque at 3000 rpm, than the best I've been able to do with the stock manifolds. Mark Kibort has great results, and Marc Thomas has shown me dyno charts with their latest headers on '85/'86S, S4, and GTS. Very impressive gains. Tom designed his crossover headers (Scavenger) for peak benefit at low/midrange, so it would be reasonable to expect that his gains will enhance the low and mid range more than the upper end where peak power is measured. How does the low and midrange compare to Devek's? I don't know. We'll never know how these header & exhaust systems stack up until someone does a back to back test between them on the same car, on the same dyno. Big job. Louie '90GT