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Old 09-26-2009, 01:17 PM   #1  
JonL1
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Default Magnaflow backpressure issues

hi,

just spoke to a guy at a local muffler shop and he told me that i can actually LOSE hp if i go with a magnaflow catback system because there's not gonna be enough backpressure. what do you guys think?


thanks
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Old 09-26-2009, 10:46 PM   #2  
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You don't want any back pressure at all. Back pressure is basically a myth created by people that don't understand what pressure wave tuning is or how fluids actually flow. You don't want to go too large because it can reduce flow velocity and actually slow flow down, but you'd have to go pretty big to experience that. Depending on power levels, anywhere from 2.5-3" is fine.
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Old 09-26-2009, 10:52 PM   #3  
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That's total bs! Stick with 2.5" and you'll be fine!
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Old 09-29-2009, 01:26 PM   #4  
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For horse power, the BEST muffler is NO muffler.
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Old 09-30-2009, 09:02 PM   #5  
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Quote:
Originally Posted by 67mustang302 View Post
You don't want any back pressure at all. Back pressure is basically a myth created by people that don't understand what pressure wave tuning is or how fluids actually flow. You don't want to go too large because it can reduce flow velocity and actually slow flow down, but you'd have to go pretty big to experience that. Depending on power levels, anywhere from 2.5-3" is fine.
Seriously? You feel 3" duals on a N/A 4.6 is fine? "No back pressure at all" you say??
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Old 09-30-2009, 09:27 PM   #6  
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Quote:
Seriously? You feel 3" duals on a N/A 4.6 is fine? "No back pressure at all" you say??
Seriously, he said depending on power levels, 2.5-3, not 3" duals on a N/A 4.6 is fine. And he is completely right in the theory of fluid dynamics. Any backpressure would turn laminar flow to turbulant flow. Which is bad in high horsepower cars, which is exactly why cars like nhra pro-drags and nascar have open pipes.

Go figure, like rocket science under this guys nose and he still tries to act like it's not written in english.
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Old 10-01-2009, 06:31 AM   #7  
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Seriously, he said depending on power levels, 2.5-3, not 3" duals on a N/A 4.6 is fine. And he is completely right in the theory of fluid dynamics. Any backpressure would turn laminar flow to turbulant flow. Which is bad in high horsepower cars, which is exactly why cars like nhra pro-drags and nascar have open pipes.

Go figure, like rocket science under this guys nose and he still tries to act like it's not written in english.
Cars like top fuel drag cars have open exhaust because they make +6000 horsepower & have fuel lines the size of garden hoses.. Have you seen the huge flamethrower flames coming out of the exhaust during night drags? Unburnt fuel igniting past the combustion chamber.. they don't care because they live in an entirely different world of requirements than a street driven car. Do you want YOUR car to have unburnt fuel in the exhaust? That'll happen with NO backpressure.

Yes you're right about fluid dynamics and the fact this issue is way more complicated than it seems. But to suggest ANY backpressure is BAD is wrong.
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Old 10-01-2009, 08:27 AM   #8  
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Do you want YOUR car to have unburnt fuel in the exhaust? That'll happen with NO backpressure.
I'd hate to have to break apart your logic here, but the unburnt fuel comes from the modification of the emissions system(more specifically the cat. converter) which removes the unburnt fuel from the exhaust. Nothing to do with the backpressure.
And yes the high horsepower cars use this method because at power levels close to 7000HP, a detail like exhaust backpressure becomes an exponential factor.
You tell me I'm wrong, prove it. And I'm not talking about trailer park rumors here. Recently alot of rumors have been dispelled about motor oil. So traditional thought is not all that you think it is.
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Old 10-01-2009, 08:47 AM   #9  
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I'm just saying much of the unburnt fuel passing through the exhaust can happen during the time both intake & exhaust valves are open (overlap period) and without sufficient backpressure a portion of the new fuel mixture will rush right past the open exhaust valve.

Yes we learn new stuff all the time, much like with motor oil like U said. But, it's been common knowledge that not enough backpressure can cause more harm than good, and that's been proven by lots of guys who idolize the drag racers & stick huge dual ehaust on longtube headers & no cats or mufflers.. they often find out sure the car is LOUDER but performance suffers. This doesn't matter to some guys who would actually prefer noise to performance but, whatever.

Hey I've got no PHD in engine dynamics so I ain't gonna post up a chart of my findings.. I just hear a LOT more often that backpressure is important..

Last edited by GreyStang; 10-01-2009 at 08:50 AM.
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Old 10-01-2009, 08:53 AM   #10  
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Well that's what rumors do to us.
The vacuum of the piston travel will take care of that overlap. And besides, just throw a spark plug in the exhaust tip and we can roast some marshmallows.
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