oneguy

iTrader: (23)

I was screwin around on the internet and found a site with some good drag data on various cars. I decided to post this site along with some pictures with data on the Evo, Sti, and Speed 6 that i found on Evom. I know some manufacturers post drag and reference area information for their cars and the program I attached will allow you to see how it stacks up against the Evo, Sti and Speed 6.

For the program you can input the coeffiecint of drag, area or the prduct of the 2. *Area must be in ft^2*

http://en.wikipedia.org/wiki/Drag_coefficient
http://www.mayfco.com/tbls.htm

Oh and if you want a laugh look at where the evo's 8.95 CdA value falls on the chart

P.S. The parent directory of the mayfco site has a lot of stuff as well
http://www.mayfco.com/analyses.htm

hexadec0079

hey what does the LBSF mean exactly... what do the rest of those numbers mean, I assume that a lower LBSF is better, my SVX has 613 LBSF to the Evo and STi 900 or so... I assume these are measures of power needed to overcome speed, I am not sure though.

oneguy

iTrader: (23)

LBSF= pounds force, FPS= feet per second, Cd= coeffecient of drag, A= area

this is measure of the ammount of force need to maintain this speed, so on level ground the evo need to exert about 57 pound of force per tire to maintain 100 mph( the 57 came from 229/4). As you can see the evo is severly hampered by drag at high speeds compared to most cars

Kordwood

I assume that's why removing the wing makes it faster. The drag on that must be significant.

inco9nito99

iTrader: (90)

Interesting...

fimotorsports

iTrader: (92)

i haven't seen where this is supported. I took the wing off and didn't gain any mph or loose any ET. I made back to back runs and they were virtually identical.

Redline06

iTrader: (45)

maybe when you are traveling faster than 130+mph is when you notice the wing no wing difference.. i mean there has to be a existent difference right.. other wise.. ama sell my wing.. j/k

oneguy

iTrader: (23)

A lot of the drag has to do with the high Cd of the evo caused by the abrupt ending of the back of the car. the rear glass isn't sloped that much compared to most high speed cars and the trunk lid is relatively short too. This truncation causes a pretty big vacuum behind the car (apparent in the rain when no water gets on your rear window until you stop) giving the evo a high Cd value. The high frontal area doesn't help with over all drag either.

David Buschur

iTrader: (53)

Very cool stuff oneguy. Do you work in the aero industry or just some college stuff you picked up?

The spreadsheet you posted, should I be able to input numbers in there for the "other car"?

Did you see the thread on the aero work I have been doing?

Thanks,

oneguy

iTrader: (23)

Just stuff from college, aero was my major but right now the only thing related to aero I do a lot of is flying. For the "other car" you just need Cd and area or the product of the two to get the drag. The preadsheet doesnt have any other losses, like rolling friction, but it will give you an idea of how much reducing surface area and drag can do to the performance of the car.

I have been following your thread for almost a week now. Very good stuff. Like a few others I bought the Beatrush under tray b/c I was tired of removing the stock one but the down side is that it was 315 shipped. If yours had been out I probably would have gone with it but thats life. I found a good site with more general aero stuff if you want to check it out:

http://superhachi.com/theory/downforce/

David Buschur

iTrader: (53)

Thanks for the link. Very easy for a dumby like me to read Seems as though I am on the right path with what I am doing aerodynamically on the EVO!

oneguy

iTrader: (23)

Yep I would agree. You could add as an option add walls to your diffuser that would create the "tunnel" mentioned in the link. I dont think it would require much extra tooling except including the 90 deg brakets to attach the walls of the tunnel to your current diffuser setup and a jig to make the roughly triangular pieces to form the sides of the wall.

Or maybe just sell the plastic in uncut form so people can make their own walls for the difffuser?

David Buschur

iTrader: (53)

I was looking at the vertical pieces that attach to the diffuser. I have been calling it a rear undertray but realize that it's actually a diffuser. What's the technical term for the vertical pieces? I either don't know or can't remember reading it. The pieces would be fairly easy to make. I might have to make a project out of it this week.

I was reading the new Grassroots Motorsports last night, it has the race from VIR in it that we were at. Also has the winning Viper driven by Tommy Archer. The aero on that car is all of this stuff we are talking about.

oneguy

iTrader: (23)

I'll see if I can pick up a copy of that magazine and check it out. To tell you the truth I don't think I know the name of them either. The author of http://www.mulsannescorner.com/ refers to them as strakes but I am not sure where to find the official terminology. Probably in a rule book for cars that are more likely to use underybody aero, but even then there may be name differences (like bonnet in th UK and hood in the US).

I don't know if there is some ruling in drag racing about how close body work can be to the ground but have y'all ever though of using an air dam to block off air from getting below the car and side skirt extensions to contain the vacuum? It seems like it would be easier than making a full flat bottom on your drag car and if very little air is getting down there in the first place then there can't be too much to cause drag.

Good luck on whatever project you end up working on next week.

-Fred

wrcwannabe

iTrader: (1)

Strakes is what I know them to be called too.

Your idea of blocking almost all the flow and using sideskirts to prevent spill air from the side entering is what i would do, but also use the flat bottom so that the remaining air flows smoothly without getting trapped and exits the rear diffuser in an orderly fashion.

Very small side spats would be of use to create a boundary layer along the side, which should prevent laminar flow.

My DD is undergoing aero mods to include the Beatrush front undertray, Buschur rear diffuser, full flat bottom, and mods/ducts on the front bumper to divert unwanted air and properly channel cooling air. Im using ideas from Corky Bell as well as what I have seen on F1 and 80-90's GTP / LMP cars.

I am going to use light oil and chalk to help see the airflow under the car. I cant use deep side skirts or go real low in the front as it is still a DD. Should still be an improvement over stock.

Milburn