Today while I was chatting it up with my F1 friend, he mentioned how 30% of the down force is produce through the rear diffuser with F1 cars. Then he asked me if the Evo has a flat under body, and obviously it does not. He said that in order for the rear diffuser to create downforce, a car would need a flat under body like so:



I was shocked! So I went to the trusty PDF file about the aerodynamics of the Evo

http://www.mitsubishi-motors.com/cor...008/20e_08.pdf

and to my surprised there is no mention of it!

someone tell me I am wrong!

 

It is a matter of degree. A flat underbody will ensure a smooth flow under the car. While an underbody that isn't flat will cause some turbulence, there will still be some laminar flow underneath the body. So the answer to your question is yes, it is functional, but won't isn't the same magnitude as that of a true race car with full underbody sheeting.

 

Absolutely .. what we see is not what the fluid sees .. its not totally flat doesn't mean its not effective ..

The flat panel can be installed if you want as an option .. but I don't think that's available over stateside ?

Thats also the reason why my rear muffler is still stock .. because going with cannister type exhaust practically just screw up any aerodynamic effects the rear bumper has

 

that is actually a good point. when i took apart the stock diffuser, i noticed the stock canister is what really makes that smooth flow to the underside of the diffuser and then out. without it, the stock diffuser looks like it's acting like a parachute. how much more drag it produces i really don't know, but i know that it does have openings on the diffuser to let out the air it inherently drags along, so i don't think it'll affect you all that much.

BUT, that said, if the stock bumper meets where the diffuser is, you can conclude that the diffuser is actually more cosmetic than anything else. like above posted, the diffuser on the x isn't exactly F1-esque or anything, and stretching the stock bumper (or an aftermarket rear bumper) down to where the diffuser is shouldn't prove to be difficult.

 

gunzo...bling it up and get the ARC exhaust ;-) It'll fill the hole plus it uh...looks dead sexy!

verkion

 

I doubt the stock diffuser is actually functional. As mentioned, it acts like a parachute, catching the air from under the car.

The Varis diffuser is probably as functional as it can be without a completey flat underbody.


I wonder if APR will make something similar, like they did to fit the stock VIII & IX bumper

 

damn that varis piece is nice...but i'd hate to wash the crevices in between the diffuser.

 

^^JUN Auto makes a front and rear diffuser for the Evo X.

 

How is the Varis a "diffuser" when it's acting more like a spoiler but to lift the car by the looks of it... If I'm wrong by what i'm seeing there, please educate me.

 

Agreed, that Varis looks dumb. It's like a slab of carbon fiber added on to the stock diffuser...

 

The rear diffuser makes a huge difference on the Evo VIII at highway speeds. We tested this theory in a cloased course. Both cars stock and all he had was the diffuser. It's about 2 cars lenght. With modds it should fly.

 

Agree with WRC Euro--- underbody spoilers should technically only help at higher speeds, more speed- more help from underbody.

I am no aerodynamics expert- but i know i dont usually cruise at 125 average all too often...

it does look sick though!!!!

 

A diffuser takes the airflow from under the car and channels it out into the low pressure area behind the car. The shape and design of the diffuser will determine how much (if any) downforce is produced. A full flat underbody will work the best with a diffuser, like the picture of the Enzo in the first post.

On a car without a flat underbody, the bottom of the body panels and rear bumper is usually lower than the bottom of the actual chassis of the car. A diffuser will help keep the airflow smoother when flowing into the area behind the car.


I made a quick drawing.

You can see without a dffuser, air can get trapped under the rear bumper, which causes a lot of turbulence and drag. A diffuser will keep the airflow smooth and out of the area under the bumper, which will decrease drag and turbulence. With less drag on the car, it can go faster with the same amount of effort.

 

Isn't the OEM ABE then acting like the diffusing you have illustrated since it will guide the air into the bumper diffuser fins?

If I'm right, wouldn't that mean that people who replace their ABE with a CBE will experience slower acceleration due to drag?

Thanks for the MS Paint art.

 

Great point that I think people often overlook.... What we see is not what a fluid "see's".

The stock bumper is already vented to prevent the parachute affect somoene else mentioned.

Gunzo, if you know where to get the OEM underbody air diffusers, please shoot me a PM... as you said, they are hard to get over here. I have plans to work on an under tray and have already got a 4'x8' 1/8 inch abs sheet to make the template, but I would like to get the mitsu parts on first. I need to dig out my magnehelic pressure gauge and get some stock underbody pressure readings first as well.....