Horse power and cat back exhaust
 

If I put a cat back strait pipe on, what will happen to the HP? I have heard that you need the back pressure or the HP will drop.

From the information I have gathered, using the supertrapp to tune by adding and removing plates, a little back pressure is good. Wide open might have more power overall, but I think you will find that the power will come at the expense of moving the power curve to higher rpms. That is a disadvantage in autocross. However, a straight pipe would be the lightest way to go and would save probably 40 pounds, so I think it would be better than not doing it, but if you went with a supertrapp, you would have the light weight with the benefit of being able to tune it. Also, some sites have noise restrictions that a supertrapp can quiet your car for.

Jake

I dont have access to a dyno, is there any way to find out how many restrictor plates would work best with a super trap on my, other wise, stock car. I guess some one else would have to had to dyno it for them selves.

FOund this info at: http://www.supertrapp.com/product_se...auto/index.asp

Dave Payne and Brian Garfield are national level autocrossers who have installed 443-2217s (brushed stainless S/C Elite 4” tunables), in their ’02 Mini Coopers. So, following their lead, I put a 443-2217 in my street ‘03 Mini Cooper. Attached is a Dyno run Dave and Brian did on the same Dyno in the same shop on different days. The baseline levels are low for a mcs, but what we all agree on is that the differences are important. I am the SuperTrapp Dyno secretary here. Brian originally thought that the 8-disc setup was best, but he has since switched to 10 discs. My car has not been Dynoed, but my buttometer also says that 10 discs are better, except for below 4500rpm, where 8 discs pull better. I continue to be amazed at how much powerband tuning is available by just changing a few discs!”G. ’03 Mini Cooper

Note: the advantages of "backpressure" is a myth. It's actually exhaust gas velocity that can help scavenge at lower RPM...smaller pipe/more restrictive muffler *can* help increase velocity (and thus help low rpm power) but can hurt at higher RPM. However, forced induction cars (supercharged Cooper Ss included) can actually benefit from LARGER diameter exhausts. I think Webb has been trying 3" piping on their MCSs.

Per
http://grmotorsports.com/news/catego...5-mini-cooper/

I'll be nabbing Webb's exhaust in the next month or so. The gains by using 3" piping is amazing!! It'll be a bit more than the average system by a couple hundred, but it will be worth the extra cash.

SPI was using 3" exhaust way before anyone else even tried it on a MINI.

Without a doubt, the Supertrapp has the most benefit of any exhaust setup. Being lightweight, tunable, and inexpensive are huge benefits/reasons to go with one.
It's been awhile since I've dealt with any of the numbers, but I can tell you that reason we went to 10 discs as stated was because of the STX car with a header and air intake. The torque numbers/curve was still the best around 7-8 discs on the stock car with nothing else other than maybe a K&N air filter (not intake).

For the '05 car, of which was never discussed, I simply put the same Supertrapp from the '02 car on but left it UNDERNEATH the car, just before the battery box. This eliminated some extra weight, and the need to have it exit and possibly melt the rear fairing. The melting part is no big deal and doesn't look bad, but is "technically" not legal.
After a season of that location, I would not recommend that location for everyday drivers of their Cooper S. It was louder and caused some annoying vibrations in the cabin, all of which I was willing to live with in my car.

The car was dynoed again going from stock to the old used Supertrapp and only saw a 2-3hp/tq. gain. Conditions were very different, but in the end, I have a feeling that the old Supertrapp was no good either. I didn't care simply because there was a gain, no matter how little,
and the obvious significant weight loss. My guess is that a Supertrapp that hadn't been touched for 35k miles was probably not at it's peak performance.

I spoke to Bob Tunnell at the Oscoda Pro last year when his wife Patty was driving a Cooper S with no muffler, just a pipe bent to go around the battery box. At the time, he had just thrown it on and had no data other than the obvious weight loss. Had I not done the Supertrapp again, I was simply going to do the same thing but with a "cherry bomb" style muffler before the battery box. In fact, my local shop was going to weld the stock tips back on for that "sleeper" look (not sound...).

Anyhow, I think most of the gains are insignificant. In the end, it's simply another way to loose a good bit of weight. So, do what you can live with, sound-wise, that drops the weight, whether it be a straightpipe, cherry bomb, or Supertrapp.

Brian

Brian, How many discs did you end up running on the 05? I have run between 6 and 8 discs on mine and felt a definate difference between the three combinations on my highly calibrated butt Dyno.

I never changed the discs when I put it in the '05, which may be why I saw less of an increase. I recall it being 8 discs, but couldn't tell you now. I guess that's my point, it became less critical in my mind. But, I would suggest starting with a new one in the '05, simply because I think there may be different results in the curve.

Brian

I just took my factory exhaust off, and I weighed it on an accurate UPS scale at work, and it came in right at 48lbs!!!! So....a straight pipe weighing about 5-6lbs would net you the 42lbs. Then adding a SuperTrapp, that weighs another 6lbs, to the straight pipe would net you about a 36lbs savings. I chose to do a single sided QuickSilver that weighed 21lbs. So I saved 27lbs, and I'm satisfied with the sound and the weight savings.