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flosho

Just wondering if anyone has one of these? The one shown below is not specific to the 931 but I'm wondering if it would work. Since I have a U.S. spec car, I have a catalytic converter, is it ok if I installed one of these before the cat, and as a result, before the wastegate exhaust "j" pipe? Or will that affect the performance somehow, I wouldn't think so.

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AznDrgn · Posted: Fri Dec 24, 2004 2:16 pm Post subject:

I don't have one but I've seen the manual ones and yes they will reduce back pressure. You can either vent it to the air like they show in the diagram or you can run it around and bypass the cat. One word of warning though some safety and or emmissions inspectors may fail you if you have one of those.
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flosho · Posted: Fri Dec 24, 2004 2:23 pm Post subject:

Yeah, I'm not worried about passing any emissions test or safety test.

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Paul · Posted: Fri Dec 24, 2004 2:30 pm Post subject:

A 931's exhaust system is almost straight through already. You'll make more noise than power. Most of our CATs have gutted themselves due to old age and present very little back pressure.

And yes I have done something similar, but it was on an Opel GT back in the 70's. IMO, it was a waste of money then and now.
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White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
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flosho · Posted: Fri Dec 24, 2004 4:25 pm Post subject:

Noise is always good. It cant hurt to cut it out sooner. Less is more with these turbo cars.
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Vince Ponz · Joined: 02 Nov 2002 Posts: 3581 Location: Florida

My 79 Euro 931 doesnot have a cat or muffler. Just a Suppertrapp without rings and it has a nice sound and not too offensive. Turbo keeps it at good levels.
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"Never let them see you sweat"
77.5 924 modified track car
79 931 Euro stock
88 924S SE
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numbbers · Posted: Mon Dec 27, 2004 12:06 pm Post subject:

Keep in mind, you need some back pressure, or you will not develop any torque. These cars already suffer from a lack of torque.
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1980 924 Turbo

924guy · Posted: Tue Dec 28, 2004 12:09 am Post subject:

JCW used to sell manual models of these real cheap, i think they came with both steel cables to open them or you could get ones you had to manually unbolt the block off plates..great for a hi-output US V-8, but for our cars?? im thinking all youll get is more noise...and as said above, smaller engines dont like to loose to much exhaust gas pressure..ive got a nasty manifold leak in my 931, and i can tell you,. it doesn not like it at all...
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Eric
78 924
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flosho · Posted: Thu Dec 30, 2004 5:01 am Post subject:

Ive always thought that with a turbo car you want the least amount of back pressure possible??
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Smoothie · Posted: Thu Dec 30, 2004 6:15 am Post subject:

You want more torque when starting out and at low rpms, and more HP at higher speeds and rpms. -So exhaust systems are designed with this in mind... not too wide because that hurts torque and not too narrow because that limits HP. That electric cutout valve would be left closed at low rpms and opened for more HP once you're moving.
Another type of valve I've seen, that makes sense to me is one that operates automatically with the exhaust flow. It's a butterfly valve similar to what you see in a throttle, but the pivot point is off-center and I think it might be spring-loaded. At low rpms it provides backpressure and at high rpms and high exhaust flow it opens more for more HP. It gets attached at the end of an oversized exhaust system - basically a system that's sized for HP, with the valve automatically regulating backpressure for better torque at low rpms.

-But all that applies more to normally aspirated engines because the turbo itself provides backpressure. -But once the catalytic converters' insides are gone, the stock 931 exhaust is probably already more than adequate and a cutout would be more decorative or fun for some than useful while not providing much of a performance improvement. It might actually be more useful on an NA, but for that, my first choice would still be that backpressure regulating valve that I mentioned along with an oversized exhaust.
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"..it's made in Germany. You know the Germans always make good stuff."

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flosho · Posted: Thu Dec 30, 2004 2:57 pm Post subject:

Interesting. With this electric one I could infact leave it shut at take off and then once i hit 3k, flip the switch to open it up. Granted its 180 dollars but maybe once I get extra money it'd be a good mod.
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Smoothie · Posted: Fri Dec 31, 2004 2:35 am Post subject:

Here's the flow regulating exhaust tip -
http://www.jcwhitney.com/autoparts/ProductDisplay/s-10101/p-4365/c-10101

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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Lizard · Posted: Fri Dec 31, 2004 11:10 am Post subject:

the turbo actually creates enough backpressure itself, the less resistance after the turbo the better
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flosho · Posted: Sun Jan 02, 2005 1:06 pm Post subject:

So what would be the better way to go? the tip or the cut out? or the tip with the cut out?
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Paul · Posted: Sun Jan 02, 2005 1:14 pm Post subject:

Cut it out, please!

Put your money in your wallet and save it for the next thing that breaks.