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The Facts about Exhaust System Design in turbo cars
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07-03-2007, 11:24 AM | #1 | |
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The Facts about Exhaust System Design in turbo cars
Hi guys,
Here's a good post from a senior engineer at Garret Turbochargers from a few years ago. It was posted on a Subaru forum to clear up some of the misconceptions about exhaust scavenging, tube sizing, etc,. that some people had. It's a good read: Quote:
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07-03-2007, 11:25 AM | #2 | |
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PART 2
Quote:
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07-03-2007, 11:35 AM | #4 |
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Given the above, would the "golf tee" mod that has been described in other threads contribute to reducing backpressure, or is that just too far down the exhaust system to make any difference?
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07-03-2007, 11:40 AM | #5 |
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God Vishnu:
Any good threats here or otherwise that would shed light on how the design and implementation of N54's exhaust system compares to the guidlines articulated above? Shawn Phoenix |
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07-03-2007, 11:40 AM | #6 |
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I don't think they're connecting the dots. Better be more overt.
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07-03-2007, 11:48 AM | #7 |
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Terry,
Why don't you just come out and summarize that the article basically states that tapering down the downpipes will increase backpressure and thus make a cat-delete downpipe mod less efficient than it could be if you were to move that tapering further down the exhaust or eliminate it by maintaining a consistent pipe diameter? Stated otherwise: If you're going to delete your primary cats, you'd be better served to run 3" pipes all the way back. Especially if you're going to push the car to 500whp+. -Hegemony |
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07-03-2007, 11:53 AM | #9 | |
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07-03-2007, 11:55 AM | #10 |
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Thanks Shiv, very interesting and completely counter to what I had "Thought" regarding Turbo exhaust.
Interesting.
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07-03-2007, 11:57 AM | #11 | |
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07-03-2007, 11:57 AM | #12 | |
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Shiv,
I agree that it's overkill now. I've always heard that the guideline is a .5" per 100whp. Thus 2.5" pipes on a true dual system should carry you up to 500whp. Generally speaking, would you agree with this logic? -Hegemony Quote:
Did Riss Racing not feel that this was an issue due to the 2.5" size of the exit flange? |
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07-03-2007, 12:00 PM | #13 |
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Thus we have a dual pipe exhaust, 2.5" should be more than enough. 250hp each pipe. Is it feasible that an exhaust shop replaces the primary OEM cat's with 200 cpi metal cat's in the OEM downpipes ? How much would this be ? Could be attractive ...
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07-03-2007, 12:01 PM | #14 |
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Stock turbine flange is 3 inch... stock exhaust flang and all aftermarket flanges are 2.5 inch.
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07-03-2007, 12:03 PM | #15 | |
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On the stock downpipes they go from 3in in DIA to 2 inch in some spot. We can make the same DIA all the way through, but there are no 3 inch aftermarket exhaust systems and 3 inch flanges wont bolt to 2.5 inch flange.... wel they can but there will be a bit of a lip/wall |
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07-03-2007, 12:04 PM | #16 | |
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However, based on what Shiv said, 2.5" should be sufficient for our engine, even if it's Proceeded...
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07-03-2007, 12:06 PM | #17 | |
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Also we could always taper back further, but the stock exhaust is one peice and after market exhaust all have flanges further down in all different spots...so it would be imposible to develope a downpipe that tappers further down the exhaust that is going to be a "one size fits all" downpipe. |
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07-03-2007, 12:07 PM | #18 |
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07-03-2007, 12:10 PM | #19 |
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Yep.... 2.5" should be more than fine. Just keep piping as straight as possible. Keeping both pipes separated is also optimal. Completely understandable to taper down the pipe at the turbine exit due to packaging constraints. But again, keeping the transition smooth (not stepped) is important.
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07-03-2007, 12:12 PM | #20 | |
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07-03-2007, 12:19 PM | #21 | |
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Then what about thing little article that AA drew up... is it BS? |
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07-03-2007, 12:24 PM | #22 | |
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An X-pipe does have merit when it comes to fitment since it basically acts as a support brace. It can also be used to change the tone of the exhaust in naturally aspirated cars through basic pulse tuning. But in terms of performance in a turbo car, an X-pipe does nothing good. It just contributes to exhaust flow turbulence/backpressure. Shiv |
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