Rear diffuser, is it functional?
#1
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Rear diffuser, is it functional?
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!
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!
Last edited by jackygor; Apr 15, 2009 at 12:36 AM.
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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.
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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.
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
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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.
Last edited by EndlessRed; Apr 15, 2009 at 03:15 AM.
#6
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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
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
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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.
#12
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!!!!
I am no aerodynamics expert- but i know i dont usually cruise at 125 average all too often...
it does look sick though!!!!
#13
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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.
Last edited by ScottSpeed21; Apr 17, 2009 at 03:13 PM.
#14
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.
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.
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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
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
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.....