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      06-04-2013, 09:36 PM   #1
ECMIV
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Less Back Pressure = Bad News ??

I was talking with a buddy of mind this weekend and he mentioned that reducing the back pressure by running a cat-less exhaust set up can be bad for naturally aspirated engines. Has anyone else heard of this?
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      06-04-2013, 09:48 PM   #2
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Maybe if the exhaust tubing diameter was WAY WAY to oversized, then I could see it losing power but idk about causing damage. Its been proven over and over that removing the cats on these cars pick up large gains. Pretty much the best bang for your buck
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      06-04-2013, 09:51 PM   #3
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The car isnt going to run perfect, and it will smell. specially without tune. tuning cleans everything up. but even without a tune, it should be ok within reason.
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      06-05-2013, 11:20 AM   #4
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Quote:
Originally Posted by ECMIV View Post
I was talking with a buddy of mind this weekend and he mentioned that reducing the back pressure by running a cat-less exhaust set up can be bad for naturally aspirated engines. Has anyone else heard of this?
Bad? Not sure about that. Removing the cats adds on average 20-25 pound feet of torque from down low and through the mid-range (2-5K RPM) on an otherwise stock motor.

Someone like Malek@MRF can probably chime in on the physics behind this if so inclined but I think it has to do with the S65's volumetric efficiency.
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      06-05-2013, 12:01 PM   #5
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Strange thing is when I had my oem mod done the car felt like it was getting strangled and not smooth. But with my new supersprint its much smoother.

Before it would literally get stuck for a split sec when I lift off before dropping revs. Doesn't do it now with my new exhaust - immediate change after fitting.
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      06-05-2013, 12:15 PM   #6
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My understanding:

In general terms, the less back pressure, the better the engine efficiency. However, a tuned exhaust system (including the most important section, the manifold) will optimize scavenging and cylinder filling, but it will also have inherent back pressure. The scavenging gains obtained from a tuned exhaust system outweigh the losses of the increased back pressure it created. So as long as you can reduce back pressure and maintain (or improve) the tuned exhaust system characteristics, you will gain power.

Last edited by CanAutM3; 06-05-2013 at 01:53 PM.
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      06-05-2013, 01:48 PM   #7
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Diameter of piping will kill hp for sure. A customer requested 4 inch piping (straight pipe). It lost around 15 whp compared to our signature exhaust system from our back to back testing. It sounded amazing though!

I'm sure most of you have seen the dyno video already.If not here you go!

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      06-05-2013, 07:12 PM   #8
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That diffuser looks good! Aggressive!
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