hey, i was thinking that i wanted to exit before the rear bumper, and was looking at right before the pass. side rear tire. my car will be really low, so i thought of cutting a hole in the panel right behind the door, and right in front of the rear wheel well and putting a metal plate on the whole area from the trim down. i got the idea from those GT series championships on speed channel. what do you guys think?

 

to do this you would have to route the exhaust through the inside of the car, thats gonna get things pretty hot...

 

and you don't really want the exhaust to exit into the high-pressure zone that exists at the sides of a car, as it creates a massive amount of backpressure

 

hmmm well crap. i didnt even think of the backpressure, i just figured it was race proven b/c i saw it on race cars... also it wasnt my intention to run it through the inside of the car just have a bend going up then into the panel

 

If it was such a bad place to put an exhaust can you tell me why GT cars run that way?

 

thats my thinking.....im going to check out my under body to see how much cutting id have to do....

 

You, sir, should call Steve Millen...he'll be eager to hear this news...

 

Ooooooooohhh....

I want that car!!!!

But then again, look at the sheer SIZE of that exhaust pipe, and compare it to your one - the overall size difference compensates for the high pressure, making it into an open ventuuri, which can help to cancel-out the high pressure. I'm simply stating that home-brew side exit exhausts CAN (not WILL) reduce performance if not designed properly

 

What do you hope to gain by doing this? Seems like you would lose a little bit of weight in the exhaust system, but not that much.

 

Style, why else?

 

It's not a horrible idea. Why make route exhaust piping more than you absolutely need to. However almost impossible to do on a street driven car at all unless you want it to come out the side but hang under the body panels and be low to the ground. Here you can see the exhaust on M2's GT series car:

 

Less important for turbos and low-overlap (i.e. stock port) NA engines, but rotaries like a long exhaust for best scavenging. Not just for peak power, but -- more importanly -- for flat torque. Obviously the exhaust has to be well tuned to see the advantages, but no point in giving away free power by taking short-cuts (pun intended).

 

gizzz

 

Why are the sides of the car a high pressure zone?
I think it would be like blowing across the top of a straw sitting in a glass of soda... you've decreased the pressure at the top of the straw, so the soda rises.

 

I am proud to say ... I popped that car's hood !!!!

 

[QUOTE]Why are the sides of the car a high pressure zone?
I think it would be like blowing across the top of a straw sitting in a glass of soda... you've decreased the pressure at the top of the straw, so the soda rises.QUOTE]

It's kinda true in a way, but you also have to imagine the car "pushing" the air out of the way, so there's going to be a big wall of air for a brief moment on the perimeter of the car.

The exhaust is almost low-pressure in comparison to the air-front. It won't matter much to turbo's, because they simply force the air in/out of the engine

 

I dissagree with that statement. Turbos force feed the induction system by sucking energy out of the exhaust system. The main issue with tuning a turbo exhaust is reducing backpressure, whereas an NA is all about scavenging by the careful placement of high and low pressure zones. In this respect, a turbo exhaust is probably more sensitive to placement of the tip in a high pressure zone.

So the issue remains, is the side of the car low or high pressure? And, perhaps more importantly, how severe is the effect in either case? Well, I can't say with any authority because I've never looked into the matter, but I will note that what purpose-built race cars do is very different than what we normally do. Most people think race cars are uncompromised but that is completely false; race cars are nothing but compromises. Rules alone are a huge source of compromise, where, in this case, they usually dictate something to the effect of "the exhaust must exit behind the driver and down at an angle of x-degrees". Then the packaging of the car (low ride hight, fuel cell placement, large diameter of exhaust tubing, etc.) might dictate that the exhaust preferably exit before the rear suspension, so that almost always means just behind the passenger-side door area. Piston motors tend to prefer shorter exhausts anyway, while rotaries are the opposite. However, even piston engine race cars often "snail" up the exhaust where the passenger would normally sit, simply to make room for mufflers and such (if required). It would seem that the compromises made for rules, packaging, budget, and other reasons probably outweigh the downside (if any) to exhausting at the side of the car. Again, I cannot comment on high or low pressure in that specific area but obviously the cost is not too high for those that do it...or they wouldn't do it. This does not necessarily mean you should do it, however.

 

I'm in the same school of thought as you man, is it high pressure or low pressure?

it's kinda in-between the two I suppose, depending on the speed and conditions

 

If you adapt something because it's on a racecar, you're in the same field as the ricers with wings.

But, on topic, it probably would work. Make sure the pipe extends out of the body an inch or so, just to make sure the exhaust exit isn't on the dead layer of air which surrounds a car.

BTW - if anybody wants to actually learn about aero stuff, pick up a copy of Joseph Katz's Racecar Aerodynamics. It's got more tech in the forward than a lot of books do in their entirety. A very good read, and isn't as technical as some books, yet gets the point across better. Even has a section about the RX7!

 

what if you adapt something from a racecar to be on a racecar?
that is why its in the race car section......

 

well it looks like im going N/A so i think im going to drop the idea........ but it was a good one for you turbo FC guys out there right?

 

You are looking at a muffler right behind the wheel. Look at the exit pipe.

I bet that car has no cooling issues anywhere!

 

True, but are you building a tube-frame GT car? I thought/ASSumed you were building a tub-car.