Exhaust design... a different take?
06-08-2011, 11:19 PM
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Exhaust design... a different take?
All-
Just leafing through the new issue of R&T, and came across a question sent in to the Tech Advice section. The question was basically, "Back pressure or no back pressure for exhaust performance?".
The answer was a little interesting, considering what I've seen/know about our cars. Some exerpts from the answer:
"...on a street vehicle with catalytic converters, mufflers and plenty of joints, bends and length, it pretty much comes down to providing the most gas flow (least restriction) possible."
"We are not aware of any case, either racing or on the street, where a restriction, or 'back pressure', is beneficial to power or economy."
"We believe many people confuse backpressure with wave tuning... and because sometimes a longer or smaller-diameter pipe works better, some have been led to think that a certain amount of backpressure was helpful. Not so; it's tuning the pipe to the pressure waves that matters."
SO- what do we think about this? I am hoping to hear from some of those involved in actually designing/manufacturing exhaust systems, that have done some R&D, as opposed to the "Well I hung out at a dyno shop one day, and...". I'm thinking people like Voldemor.., er, RS Barn
, D9, etc.
Talk amongst yaselves!
Dave
Just leafing through the new issue of R&T, and came across a question sent in to the Tech Advice section. The question was basically, "Back pressure or no back pressure for exhaust performance?".
The answer was a little interesting, considering what I've seen/know about our cars. Some exerpts from the answer:
"...on a street vehicle with catalytic converters, mufflers and plenty of joints, bends and length, it pretty much comes down to providing the most gas flow (least restriction) possible."
"We are not aware of any case, either racing or on the street, where a restriction, or 'back pressure', is beneficial to power or economy."
"We believe many people confuse backpressure with wave tuning... and because sometimes a longer or smaller-diameter pipe works better, some have been led to think that a certain amount of backpressure was helpful. Not so; it's tuning the pipe to the pressure waves that matters."
SO- what do we think about this? I am hoping to hear from some of those involved in actually designing/manufacturing exhaust systems, that have done some R&D, as opposed to the "Well I hung out at a dyno shop one day, and...". I'm thinking people like Voldemor.., er, RS Barn
, D9, etc.Talk amongst yaselves!
Dave
06-09-2011, 08:29 PM
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i've tried 4 combinations and finally settled on one that's really good. backpressure is for losers. what you want is maximum exhaust speed and flow. why? because the variocam is already a high-volume breathing racing version of a classic n/a design (from the moment the variocam kicks on)... for anyone who's never heard one of our engines unplugged, all i can say is, you don't know what you're missing.
i started with the stock exhaust. it isn't terrible. it isn't very good either... and it's heavy.
next, i changed to straight pipe and a large glasspack, but that was too loud. but then, i was able to make it sound much better by adding a high-flow, hollow resonator. but, then i went back and found two much better mufflers..... now, i have an exhaust that i believe beats anything out there. one of the rennlisters, Van has heard the final edition of my little exhaust project. i played the symphony for him.
first, run 2 1/2" pipe, into a loudmouth resonator ( http://www.summitracing.com/parts/SLE-310013919/ )....
next choose either an 18" X 9" X 4" or 22" X 11" X 5" Magnaflow.... the smaller one will make an exotic sound but it will be significantly louder than stock (though nowhere near as bad as a flowmaster) at wot.... the 22" will make a much quieter 'exotic' sound — only slighty louder than stock at idle — and big, natural sound at wot — and not too loud by any standard. i've got the larger, 22" muffler stuffed in there and i absolutely love it. it still weighs less than a normal muffler and i'll run this for my LS engine swap too. the rennlisters who prefer the "factory Porsche" sound will like this final setup a lot.
get the smaller one in 2.5" in 2.5" out center to offset, or the larger one in 3" in 3" out, center to offset.
18"; http://www.magnaflow.com/02product/s...e=main&id=9211
22"; http://www.magnaflow.com/02product/s...e=main&id=9240
1. neither of these makes that compressed, 'fart-can' sound.
instead the 3.0 litre engine sounds more like a larger V6, natural and exotic all the way to the redline.
2. not loud or obnoxious. finally a straight through muffler that tames the big 3.0 four.
3. this simple upgrade will make at least 15~18 more horsepower.
*long tube headers can be added ($$$$).
.
i started with the stock exhaust. it isn't terrible. it isn't very good either... and it's heavy.
next, i changed to straight pipe and a large glasspack, but that was too loud. but then, i was able to make it sound much better by adding a high-flow, hollow resonator. but, then i went back and found two much better mufflers..... now, i have an exhaust that i believe beats anything out there. one of the rennlisters, Van has heard the final edition of my little exhaust project. i played the symphony for him.
first, run 2 1/2" pipe, into a loudmouth resonator ( http://www.summitracing.com/parts/SLE-310013919/ )....
next choose either an 18" X 9" X 4" or 22" X 11" X 5" Magnaflow.... the smaller one will make an exotic sound but it will be significantly louder than stock (though nowhere near as bad as a flowmaster) at wot.... the 22" will make a much quieter 'exotic' sound — only slighty louder than stock at idle — and big, natural sound at wot — and not too loud by any standard. i've got the larger, 22" muffler stuffed in there and i absolutely love it. it still weighs less than a normal muffler and i'll run this for my LS engine swap too. the rennlisters who prefer the "factory Porsche" sound will like this final setup a lot.
get the smaller one in 2.5" in 2.5" out center to offset, or the larger one in 3" in 3" out, center to offset.
18"; http://www.magnaflow.com/02product/s...e=main&id=9211
22"; http://www.magnaflow.com/02product/s...e=main&id=9240
1. neither of these makes that compressed, 'fart-can' sound.
instead the 3.0 litre engine sounds more like a larger V6, natural and exotic all the way to the redline.
2. not loud or obnoxious. finally a straight through muffler that tames the big 3.0 four.
3. this simple upgrade will make at least 15~18 more horsepower.
*long tube headers can be added ($$$$).
.
Last edited by odurandina; 06-10-2011 at 03:36 AM.
06-10-2011, 12:07 AM
#5
Three Wheelin'
Hi Odurandina,
Where did you put the resonator? In place of the cat?
Thanks for the part numbers, if you could show a sketch showing location that would be helpful!
Thanks,
Mike
Where did you put the resonator? In place of the cat?
Thanks for the part numbers, if you could show a sketch showing location that would be helpful!
Thanks,
Mike
06-10-2011, 12:12 AM
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in the tunnel about halfway between the where the cat and resonator used to be.
that muffler has a smooth 'S' curve inside.
that muffler has a smooth 'S' curve inside.
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06-10-2011, 02:29 PM
#8
Bannana Shine
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I'd really like to see somebody write a program that will model an engine's exhaust pulses and simulate their flow through whatever exhaust design the user wants to test. Would be much too expensive for the hobbyist, but could help tuning shops improve their products while decreasing development costs and time.