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462avi
Joined: 15 Sep 2006 Posts: 149 Location: Hollister, California
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Posted: Fri Nov 17, 2006 1:21 pm Post subject: waste gate exhaust |
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Hey guys
Has anyone disconnected the pipe from the waste gate to the stock cat? If so was there any ill affects other than noise. The reason I as is I have a friend of mine who is going to weld me up a new exhaust pipe. The po had an aftermarket cat welded in behind the original and also removed the guts from the original. I want to eliminate the original but I need to know if the wastegate exhaust is actually necessary. What do you think.
Geoff _________________ 2005 C230K
2002 grand cherokee with 4.7L |
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macBdog
Joined: 16 Aug 2004 Posts: 1111 Location: Brisbane, Australia
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Posted: Fri Nov 17, 2006 1:58 pm Post subject: |
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I know some 944 guys on rennlist do this. They say it sounds pretty good when you hit top boost like a wooshing sound. I don't think youd see any power gains from it at all compared to the stock setup. _________________ 1979 931 with a 350 chev
1973 911E with EFI
p-talk wrote: | I'm still convinced the word 'Porsche' makes people crazy in all kinds of ways |
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SoyRacer
Joined: 25 May 2003 Posts: 156 Location: Long Island, New York
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Posted: Fri Nov 17, 2006 6:18 pm Post subject: |
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I Did This On My CGT Project Before I Dismantled The Car For The Engine Rebuild And I Honestly Do Believe That It Did Help Performance. The "Wasted" Gasses No Longer Have To Be Crammed Back Into An Exhaust That Is Flowing At A Very High Rate. I Used A Very Slender Motorcycle Muffler And Welded Up Mounting Tabs That Supported It Next To And Just Slightly Below The Center Resonator. I Weled A Turndown To The End Since It Ended Under The Car Just In Front Of The Transmission.
The Main Reason That I Think It Helps Is That This Particular Car Was A U.S. Spec Car With A Catalytic Conv. And The Wastegate Used To Dump Back Into The Exhaust Just In Front Of The Cat. Can You Say "BackPressure" ?
My Euro 931 Has No Cat. So I Never Really Saw That There Would Be Any Real Performance Advantage.
Anyway, Good Luck !! _________________ 1973 911-RS 3.2 Track Car
1981 Porsche 931/Carrera GT Project
1981 Porsche 931 Euro W/CGT Intercooler
1984 Porsche 944 Gutted Track Car
1987 Porsche 924s Rally Style (sold 3-2012)
2000 Chevy C-2500 Pick-up
2004 Subaru Forester STi |
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bass gt
Joined: 02 Dec 2004 Posts: 971 Location: Johannesburg for now!!
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Posted: Sat Nov 18, 2006 1:01 am Post subject: |
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Guy's,
just to echo what Soyracer said. It is well worth venting the WG away from the stock position. Even though my car is a Euro 931, it makes a big difference. The best way is to reconnect the WG pipe about 12" from the exhaust end, as it then acts in scavenging the exhaust system. However, this is not really practicable on our cars, so just vent it to atmosphere and away you go. noise is like ripping canvas at full boost!! Sound good, especially on my racer.
Steve |
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462avi
Joined: 15 Sep 2006 Posts: 149 Location: Hollister, California
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Posted: Sat Nov 18, 2006 1:30 am Post subject: |
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Thanks guys
I figured that it was just to muffle the wastegate and I did not want to connect it if I did not have to. For me it is not really for any performance gain. Like I said I am having a replacement made for the stock cat/resonator and it is just one less hassle.
Geoff _________________ 2005 C230K
2002 grand cherokee with 4.7L |
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Min
Joined: 04 Nov 2002 Posts: 2368 Location: Vernon, British Columbia, Canada
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Posted: Sat Nov 18, 2006 3:12 am Post subject: |
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How do you properly measure A/F ratio if you do this?
Min _________________ Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting. |
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-nick
Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA
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Posted: Sat Nov 18, 2006 4:42 am Post subject: |
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There should still be plenty of exhaust going through the turbo and past the o2 sensor. The only difference is that it may be picking up less exhaust from #4 cylinder when the wastegate is open.
ps - I would check with Cal laws before you mess with it... _________________ 1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet |
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Min
Joined: 04 Nov 2002 Posts: 2368 Location: Vernon, British Columbia, Canada
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Posted: Sat Nov 18, 2006 4:47 am Post subject: |
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-nick wrote: | There should still be plenty of exhaust going through the turbo and past the o2 sensor. The only difference is that it may be picking up less exhaust from #4 cylinder when the wastegate is open.
ps - I would check with Cal laws before you mess with it... |
see, I'm more concerned about losing not fully mixed exhaust gases through the wastegate so getting a incorrect a/f ratio reading.
Min _________________ Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting. |
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-nick
Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA
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Posted: Sat Nov 18, 2006 5:10 am Post subject: |
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The wastegate is plumbed into the stock exhaust after the o2. In fact I think that's usually the case. I would bet that any effect on the o2 would be pretty minimal? _________________ 1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet |
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462avi
Joined: 15 Sep 2006 Posts: 149 Location: Hollister, California
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Posted: Sat Nov 18, 2006 6:07 am Post subject: |
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The waste gate is plumbed in after the stock cat into the first resonator. I am pretty sure that this was just a way to muffle the wastegate when it actuates.
As far as smog is concerned yes there may be an issue but since the wastegate is not always going to be actuated I still don't see any real big problem.
Geoff _________________ 2005 C230K
2002 grand cherokee with 4.7L |
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Peter
Joined: 04 Nov 2002 Posts: 379 Location: New York, NY
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Posted: Tue Nov 21, 2006 8:44 am Post subject: |
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If CA still does a visual inspection, which I believe it does, you will have a problem by venting the WG exhaust into the air.
Why not plumb it into a secondary CAT?
Let us know how it turns out, as I am planning a move to SF in a few years and I am intertested in how the 931 does in CA testing. |
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Paul
Joined: 02 Nov 2002 Posts: 9491 Location: Southeast Wisconsin
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Posted: Tue Nov 21, 2006 10:51 am Post subject: |
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The secondary cat will never get up to operating temps on the street... _________________ 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
Porsche: It's not driving, it's therapy. |
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Peter
Joined: 04 Nov 2002 Posts: 379 Location: New York, NY
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Posted: Tue Nov 21, 2006 2:26 pm Post subject: |
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Paul wrote: | The secondary cat will never get up to operating temps on the street... |
Sure, but as he stated earlier, his concerns are not emissions. The 2nd CAt is an attempt to pass visual inspection, which CA has. I don't think any smog inspector would pass a car with an exhaust pipe that vents directly to the air, regardless if its from the WG or the manifold directly. Unless of course the inspector is a friend. |
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462avi
Joined: 15 Sep 2006 Posts: 149 Location: Hollister, California
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Posted: Wed Nov 22, 2006 2:36 am Post subject: |
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I guess I may have confused some with the way the car is currently layed out. The original cat has been gutted by the p.o. That is why the aftermarket cat was installed. The cat should get up to temp just fine in its configuration. That being said I will probably relocated it further up the exhaust stream just to be on the safe side. I plan on venting the waste gate overboard. The smog inspection in ca is stringent but as far as the visual is concerned it is mainly for the underhood stuff. I can not ever remember an inspector climbing under one of my cars to check connections. If the aftermarket cat is functioning then it should pass the computer test as well. Hopefully this clarifies things alittle.
Geoff _________________ 2005 C230K
2002 grand cherokee with 4.7L |
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flosho
Joined: 01 Jul 2004 Posts: 3155 Location: Eau Claire, Wisconsin
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Posted: Wed Nov 22, 2006 5:27 am Post subject: |
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Min wrote: |
see, I'm more concerned about losing not fully mixed exhaust gases through the wastegate so getting a incorrect a/f ratio reading.
Min |
Like Nick said, the stock o2 is only 20" after the turbo and the wastegate doesn't join the turbo back exhaust until a good 2+ feet later in the center of the cat.. I would bet a paycheck that there wouldn't be any legit difference in measuring a/f between the setups. _________________ [This Space For Rent] |
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