Twin dump or bellmouth?
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From: St. Louis MO
Car Info: 02 PSM WRX
Twin dump or bellmouth?
What is better twin dump downpipe or bellmouth? I would think twindump but I dont want to eliminate any cats. Is there a twin dump that enters the exhaust stream farther down that has a highflow cat (or is that possible?)? I would think the farther down the 2 pipes merged to 1 the better. I already have a Blitz Nurspes R cat back and Im wanting to finish the turbo back with 2 highflow cats. Will I pass emissions with the highflow cats? I live in Missouri and dont know how tough the test is so would It pass in California?
Thanks
Thanks
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Air Power Systems and Cobb Tuning both recommend bellmouth.
They say they did a lot of testing.....?
www.cobbtuning.com
http://www.aps-wrx.com/products_usa.html
They say they did a lot of testing.....?
www.cobbtuning.com
http://www.aps-wrx.com/products_usa.html
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From: Rockin my 6th Suby in the 808 in the past decade!
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California Emissions are some of toughest in the world. Last time I checked it was illegal to modify your exhaust. but that was a long time ago. if anything it might be worst than it was. goodluck
4080
4080
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Why do you want 2 cats after the turbo? If you want to stay 100% legal then you're stuck with the stock system from the turbo to the cat. If you're looking to be able to pass a "sniffer" test than just 1 high flow cat will do it as long as it's warmed up good before the test.
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The question of which dp design is the best will never die. There are basically 3 designs: Flate Plate, Bellmouth, Divorced.
The flate plate design isn't terrible, it just isnt the most effective. When the exhaust leaves the wastegate, it hits the wastegate door at and angle that directs it towards the 3" opening.
The Bellmouth is a good design with one exception. The exhaust gas gets very turbulane right behind the turbo. That seems to be the only flaw in the bellmouth design.
The divorced pipe is IMO the best design. The exhaust gases from the exhaust outlet and the wastegate dont mix until farther down the dp. B/c of this, the exhaust flows much more smoothly.
The flate plate design isn't terrible, it just isnt the most effective. When the exhaust leaves the wastegate, it hits the wastegate door at and angle that directs it towards the 3" opening.
The Bellmouth is a good design with one exception. The exhaust gas gets very turbulane right behind the turbo. That seems to be the only flaw in the bellmouth design.
The divorced pipe is IMO the best design. The exhaust gases from the exhaust outlet and the wastegate dont mix until farther down the dp. B/c of this, the exhaust flows much more smoothly.
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From what I've read the dived DP design is best since it separates the wastegate and turbo exducer exhaust flows. As Dallas P&P said, things are pretty turbulent when the exhaust gases exit the turbo and turbulence is bad. A venting wastegate will only add more turbulence (two exhaust gas flows colliding) at the point where exhaust gases exit the turbo, in the case of a Bellmouth DP design for example.
In the case of a divorced DP design, the wastegate and exducer exhaust gases are "reunited" much further down stream, where things are a lot calmer.
My .02 cents.
In the case of a divorced DP design, the wastegate and exducer exhaust gases are "reunited" much further down stream, where things are a lot calmer.
My .02 cents.
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From: Tucson
Car Info: '02 WRX WRB
The Vishnu twin-dump lets the wastegate gas pass the highflow, like you're looking for. But every tuner I know of recommends the bellmouth for stock turbo applications. The superiority of the divorced wastegate will only be evident with bigger turbos.
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Originally posted by Mister 2
Why do you want 2 cats after the turbo? If you want to stay 100% legal then you're stuck with the stock system from the turbo to the cat. If you're looking to be able to pass a "sniffer" test than just 1 high flow cat will do it as long as it's warmed up good before the test.
Why do you want 2 cats after the turbo? If you want to stay 100% legal then you're stuck with the stock system from the turbo to the cat. If you're looking to be able to pass a "sniffer" test than just 1 high flow cat will do it as long as it's warmed up good before the test.
Thanks
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The Vishnu signature series exhaust uses a twin dump and can be ordered with a hiflow cat. However, it does not have the third cat. It will pass the sniffer test, but not the visual if the tech is expecting to see 2 cats after the turbo. Of course, you could always weld another cat in if you wanted to.
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Since most of the bellmouth downpipes only have the third cat would I be better off getting a catless downpipe and installing a high flow cat closer to the turbo or would this be bad for flow? The only reason I ask is because in the past I have had to wait 20 minutes in line to have the test done and by that time the cat would be cold. If I have to I will just change it every 2 years for the test. Thanks to all of you for the replies,
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From: St. Louis MO
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Originally posted by VRWRX
Just keep your engine running while you are waiting in line
Just keep your engine running while you are waiting in line
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if you want to pass a visual inspection just get some heat shields in place where the 3rd cat should be. Im pretty sure wrx's arent popular enough yet that every mechanic knows it has 3 cats. Also if you have a utec you might be able to make a smog map...aka program computer to help you pass smog.