[kach22i]

Originally Posted by razordave

In my mind I'm building a small diffuser for the bottom side of the pseudo boat tail and the exhaust will vent inside the box.

What I am worried about is poisonous diesel exhaust making its way back into the cabin. Do I need additional air introduced at the same plane? Maybe route the radiator air between the floor pans and under tray?

Aren't all exhaust fumes corrosive?

In any case they contain a lot of moisture, you can sometimes see water or other liquid dripping out the tailpipe.

You do not want to trap or collect this in any way in my opinion.

I did a quick search on this topic, and it looks like one solution is to use the force of the exhaust to induce more airflow along a diffuser plane.

Exhaust Blown Diffuser

Blown diffuser on Senna McLaren-Honda MP4/7A during Mexico GP 1991. He suffered a big accident at the high speed Peraltada corner during qualifying, in which the car rolled and landed upside down) but thankfully he emerged unscathed.

In recent years, the effect of the exhaust on the centre of pressure, and its variation with throttle opening have led to the true blown diffuser being abandoned,............

Effectively the harder the air flows over the diffuser, the more powerful the gurney can be in puling airflow from inside the diffuser; this makes the diffuser act as though the exit is larger and makes more downforce.

You may not have a race car that needs extra down-force, but the examples in that article show that there is more than one way to do things.

And none of them allow exhaust gases to collect in an open ended box.

Maybe this visual below can be used to establish a concept or at least a launching point for one.

http://www.rapid-racer.com/aerodynamic-upgrades.php


I'm assuming that the exhaust will be at both a higher pressure and faster velocity than the rest of the air leaving the underside of the car.

I know that under normal circumstances the faster moving the air the lower the pressure, and the slower the air is moving the higher the pressure.

However, the exhaust has the energy of the entire engine behind it, it's not like the normal air going under, over and around the car, right?

I'm visualizing the exhaust as a continuing firing shot gun blast, just to get my big picture going.

Maybe a fire hose or a waterjet on a jetski are better compatibles?


Rear Diffuser and Exhaust Gases:
http://www.rapid-racer.com/aerodynamic-upgrades.php

By incorporating the exhaust system into the rear diffuser, you can also help extract the air from the rear of the car more effectively. The exhaust gasses produced effectively energise the airflow, helping to raise the low pressure air the diffuser creates by amplifying the suction effect. This fast moving air flow returning back to the ambient atmospheric pressure at the exit of the diffuser, reducing drag levels. Hot exhaust gases also aid in expansion, again aiding in the airflow speed transition between fast moving underbody air and slow moving ambient air. Resulting in higher vacuum effect, more downforce and reduced drag.