Back Pressure
06-02-2006, 06:22 PM
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Back Pressure
Can somone explain to me the theory of Exhaust Back Pressure. 2.5 vs. 3in? Does a suppercharged car want more or less back pressure? Does a N/A car want more or less back pressure? How does it affects Tourqe and preformance in general?
Please don't give oppinians, I just want to know the strait facts from somone who knows a lot about this toppic
Thanks a lot for the help
Please don't give oppinians, I just want to know the strait facts from somone who knows a lot about this toppic
Thanks a lot for the help
06-02-2006, 06:28 PM
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I'm not an expert by any means, but whoever wrote this article seems to know their stuff.
06-02-2006, 06:38 PM
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Originally Posted by Vette Jr.
Thanks,
So what I got from that is that bigger exhaust is better for a S/C engine... Correct?...
So what I got from that is that bigger exhaust is better for a S/C engine... Correct?...
06-02-2006, 06:38 PM
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It's not just backpressure but also exhaust velocity. Boosted vehicles use bigger exhaust systems because the exhaust velocity is much greater and back pressure is less needed.
06-02-2006, 06:41 PM
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For supercharged and turbocharged vehicles, one should use no less than a 2.5 inch exhaust system. Forced induction vehicles with a 220ci or larger engines can use 3 inch exhaust.
06-02-2006, 06:43 PM
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bigger is better to a point, you need a certain amount to keep your torque constant. a lot of people putting a 3" on a stock car are seeing their torque curve fall off. it has something to do with the exhaust not getting hot enough to scavenge the gases like it should or something, so the gases start to cavitate and don't move like they should. a 2.5" exhaust seems to be good up to about 320hp or so.
turbos seem to react better to completely free-flowing exhausts, IMO because they don't seem to rely so much on the exhaust as the turbine in the exhaust half of the turbo itself for resistance.
just my $0.02 FWIW.
turbos seem to react better to completely free-flowing exhausts, IMO because they don't seem to rely so much on the exhaust as the turbine in the exhaust half of the turbo itself for resistance.
just my $0.02 FWIW.
06-02-2006, 10:54 PM
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I think it is a Flip of a coin really.... I am Contemplating the same thing you are but I am getting stage 4 but I don't know if I want a 3" exhaust around here just because the cops are DICK'S
06-03-2006, 12:29 PM
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Originally Posted by Vette Jr.
so in the end... would you use a 2.5 or 3 on the LSJ(stock)?, LSJ STG2?
Like the guys said, 2.5 is adequate. If you plan on going up over 350 HP then go 3".
06-03-2006, 01:23 PM
#15
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Originally Posted by Matty
Like the guys said, 2.5 is adequate. If you plan on going up over 350 HP then go 3".
The reason guys with turbochargers get such big exhaust systems is because the less backpressure they have, the faster and easier their turbines spin inside their turbochargers. Other ways of achieving this besides getting an overall big exhaust system is by doing an exhaust cut out (basically makes you have a huge exhaust leak) or running open downpiped (like I'm doing currently
).
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