Rerouting exhaust to a low pressure point

[ConnClark]

I'm thinking of trying to reroute my exhaust to a low pressure point to reduce exhaust back pressure. If I route it to the back of the car in the slip stream it should also reduce drag slightly. As I see it I would get almost nothing but gains. Less back pressure, slightly more boost, and slightly less drag.

The only potential problem I see is diesel soot getting on the back of my car.

[MazdaMatt]

Before you start buying piping, i'd suggest that you figure out the psi difference between where you exhaust is now and the back of your car. I'm guessing it is minimal. I'd also figure out the cfm of air coming out your pipe and what affect that may have on the your drag. I'm guessing both are minimal and your net gain will be zapped by the extra 2 feet of pipe you're carrying around.

[winkosmosis]

Where is the exhaust now?

I wouldn't mess with the exhaust system. If you screw up an aeromod, the worst case is some holes in your body or scratched paint. If you mess up exhaust, the worst case is fumes in the cab, CO poisoning, brain damage, or death.

[ConnClark]

Right now my exhaust exits right below the bumper on the drivers side. I could get it to route just above the bumper with a slight bend just in front of the muffler and a 6 inch extension. The exit would be right in the slipstream then and hence in a slight vacuum.

I would have to cut the body work which makes me uneasy with this mod.

Edit: CO poisoning isn't a problem on diesels unless they are way out of tune. Fumes wouldn't getting into the passenger compartment wouldn't be a problem anyway

[Frank Lee]

Maybe a manometer test would reveal it's already in a low psi zone?

[DonR]

Couldn't you take it to a local muffler shop & have them make a clamp on extension to route it to where you want it? If you smell more exhaust than normal or you get more soot than you can stand, unclamp it.

[ConnClark]

Originally Posted by Frank Lee

Maybe a manometer test would reveal it's already in a low psi zone?

I kind of doubt that. The slip stream always has a lower pressure than something in the air flow. Also recent trends in car design have moved the exhaust outlet from below the bumper to a notch in the bumper or as part of back of the car to leverage this vacuum. A Porsche boxster is an example of this

[Frank Lee]

"The slip stream always has a lower pressure than something in the air flow."

Where'd ya learn that?

[instarx]

An exhaust pipe in the airstream will have air travelling down the outside of the exhaust pipe and past the end of the pipe. This causes a low pressure area immediately beyond the end of the pipe due to the Bernoulli effect (turning a duct into an exhaust duct by blowing compressed air past it's open end is a common engineering trick when internal fans cannot be used, for example when exhausting explosive gases). Relocating the exhaust's end-point to a low pressure area behind the car would eliminate that particular pressure advantage. But which would be more effective... the Bernoulli drop or the low pressure area end-point? IMHO the difference in exhaust flow between the two would be so small as to be essentially immeasurable even with instrumentation.

A much more effective method to reduce exhaust back-pressure would be to install a larger diameter, straighter, or shorter exhaust pipe.

[tasdrouille]

I honestly don't think it'll make a difference. I'm planning to have mine exit in front of the driver side rear wheel, might not change a thing to FE, but I love the sound of a spooling turbo too much to have it exit out the back.