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waste gate exhaust

 
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462avi  



Joined: 15 Sep 2006
Posts: 149
Location: Hollister, California

PostPosted: Fri Nov 17, 2006 2:21 pm    Post subject: waste gate exhaust Reply with quote

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
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macBdog  



Joined: 16 Aug 2004
Posts: 1110
Location: Brisbane, Australia

PostPosted: Fri Nov 17, 2006 2:58 pm    Post subject: Reply with quote

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.
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SoyRacer  



Joined: 25 May 2003
Posts: 155
Location: Long Island, New York

PostPosted: Fri Nov 17, 2006 7:18 pm    Post subject: Reply with quote

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 !!
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bass gt  



Joined: 02 Dec 2004
Posts: 971
Location: Johannesburg for now!!

PostPosted: Sat Nov 18, 2006 2:01 am    Post subject: Reply with quote

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

PostPosted: Sat Nov 18, 2006 2:30 am    Post subject: Reply with quote

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
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Min  



Joined: 04 Nov 2002
Posts: 2368
Location: Vernon, British Columbia, Canada

PostPosted: Sat Nov 18, 2006 4:12 am    Post subject: Reply with quote

How do you properly measure A/F ratio if you do this?

Min
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-nick  



Joined: 16 Nov 2002
Posts: 2699
Location: Cambridge, MA

PostPosted: Sat Nov 18, 2006 5:42 am    Post subject: Reply with quote

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...
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Min  



Joined: 04 Nov 2002
Posts: 2368
Location: Vernon, British Columbia, Canada

PostPosted: Sat Nov 18, 2006 5:47 am    Post subject: Reply with quote

-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
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-nick  



Joined: 16 Nov 2002
Posts: 2699
Location: Cambridge, MA

PostPosted: Sat Nov 18, 2006 6:10 am    Post subject: Reply with quote

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?
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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

PostPosted: Sat Nov 18, 2006 7:07 am    Post subject: Reply with quote

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
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Peter  



Joined: 04 Nov 2002
Posts: 379
Location: New York, NY

PostPosted: Tue Nov 21, 2006 9:44 am    Post subject: Reply with quote

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
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PostPosted: Tue Nov 21, 2006 11:51 am    Post subject: Reply with quote

The secondary cat will never get up to operating temps on the street...
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Peter  



Joined: 04 Nov 2002
Posts: 379
Location: New York, NY

PostPosted: Tue Nov 21, 2006 3:26 pm    Post subject: Reply with quote

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

PostPosted: Wed Nov 22, 2006 3:36 am    Post subject: Reply with quote

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
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flosho  



Joined: 01 Jul 2004
Posts: 3153
Location: Eau Claire, Wisconsin

PostPosted: Wed Nov 22, 2006 6:27 am    Post subject: Reply with quote

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.
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