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81turbo Guest
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Posted: Sat Jun 29, 2002 2:45 am Post subject: |
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Hi I am considering buying a Borla cat back from a 951 for my 931. The claim is that this unit gives a 12hp gain on a 951. Do you guys think it would have any hp value on a 931? Is the factory system restrictive? It seems pretty huge to me, what do you think?
Ryan |
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Zuffen
Joined: 31 Jul 2001 Posts: 1426 Location: Owasso, Oklahoma 74055
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Posted: Sat Jun 29, 2002 2:53 am Post subject: |
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It is bigger than the 924S and 944 and from what I can tell either the same or bigger than a 951.
I just did some comparison for a guy needing a 931 exhaust and I was very surprised to see it being larger than the 2.5 liter cars. So the exhaust on a 931 is not restrictive to any measure.
_________________ Bob Dodd - 924turbo@cox.net
931 1982, 944 1982 euro, 924S 1988SE, 93 968 tip 06 Silver Cayenne S, 06 Black Cayenne S
I have Way too many cars, parts for the 931,944 and 951 |
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81turbo Guest
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Posted: Sun Jun 30, 2002 7:32 am Post subject: |
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come one guys, what no advice? thanks Bob |
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Rick MacLaren Guest
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Posted: Sun Jun 30, 2002 9:29 am Post subject: |
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I wouldn't bet on winning the Indy with a Borla exhaust. I'd go with a 944 one or 931 any day. Unless you're going for a 3" exhaust and can benefit from the cooling, I can't see the benefit. After all, you've got a cat there, right? |
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John H Guest
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Posted: Mon Jul 01, 2002 9:25 am Post subject: |
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I carried out some tests in the late 80's on a factory stainless steel system (euro) for a 931 and various other combinations and found the factory system was almost spot on.
Some performance gains can be found by playing with the mufflers but the size of the pipe is pretty musch righ unless you start playing with really high boost.
To gain the best out come you need to spend time on a rolling road dyno. I had access to one then and the only cost was my time in swapping the exhausts systems over. At the end for racing I still used the standard system unless I was on a short tight course in which case I took the back muffler off and ran a 3 inch pipe gave a bit power down low (not much more) but meant that I could dump about 10 to 20 kilos of weight in the back muffler and associated brackets. On long courses the removal of the back muffler caused me to lose places so it went back on.
[ This Message was edited by: John H on 2002-07-01 09:30 ] |
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81turbo Guest
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Posted: Mon Jul 01, 2002 12:57 pm Post subject: |
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I am proud to say that I did not buy the exhaust (ie saved $200) but that is only because it was damaged in the crash. This guys car was really messed up. As far as the exhaust, it was very nice but damaged. Also I am not running a cat. I do have one on the car but it is REALLY hollow. P.S. don't tell California! thanks John for the insite. |
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Rick MacLaren Guest
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Posted: Tue Jul 02, 2002 12:46 am Post subject: |
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If your cat is hollow, and you've got a stock 931 exhaust, you've probably got the best combination you can get. |
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larso Guest
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Posted: Tue Jul 02, 2002 6:25 pm Post subject: |
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How about a side pipe with a shorter exhaust? I'd say since it's a turbo the stock exhaust could lose a few bends and turns. Shorten it up until the flame starts coming out, then lengthen it LOL. I plan to run a straight through muffler out the side behind the front wheel but don't know where to hang it and don't really have time... Will sound cool even if it only gets 1HP in the high RPMS, since the cops don't care here and no emmissions in EDMONTON. |
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Rick MacLaren Guest
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Posted: Wed Jul 03, 2002 10:03 am Post subject: |
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Know what I'd like? A STRAIGHT PIPE, right out the side like you mention, Lars, and a springed release I could use inside the cabin to pull when I want it opened. |
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John H Guest
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Posted: Wed Jul 03, 2002 10:24 am Post subject: |
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I've run the car with a straight pipe and no muffler and it sounds like shit, and performs like a dog.
You should have a muffler of some sort just to get abit of back pressure into the system to make everything work. |
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Rick MacLaren Guest
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Posted: Wed Jul 03, 2002 10:26 pm Post subject: |
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It didn't help way up in the higher RPM's? Like, 5000 or so? |
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numbers Guest
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Posted: Thu Jul 04, 2002 7:27 am Post subject: |
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If you run no muffler at all, you will not get any low end. And, of course with a turbo, low end is what you need. It takes back pressure to build low end torque. I am not up on the physics of this, just speaking from experience. That being said, the factory muffler has a little two much back pressure to let the turbo spin up as fast as possible. I run a Borla 2.5 inch muffler with the factory pipes, and a gutted cat. When I switched to the Borla, there was a noticable gain in acceleration. I haven't tried any other pipes, as the factory stuff seems adequate, and I do need to pass emissions for another three years. |
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larso Guest
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Posted: Wed Jul 24, 2002 12:04 am Post subject: |
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well a turbo IS back pressure. Usually a more flowign exhaust in a turbo can't do any harm unless you see flames coming out? Why does the straight pipe make the car perform like a dog?? I'm curious since a turbocharger creates TONS of back pressure. You can't tell me a turbo doesn't restrict the exhaust enough already. What do you think is the reason John H, I just can't see a turbocharged car needing ANY back pressure, I just see it needing soem pipe length so that flames coming out don't screw things up (overheat, melt, etc.) |
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Vince Ponz Guest
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Posted: Mon Jul 29, 2002 11:19 pm Post subject: |
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I run no cat but a resonator and a Supertrapp end without the cap or rings. Sounds nice and runs very well. It is a 79 Euro and did not have a cat.
Louder exhaust note adds 5 HP |
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