Downforce needed - battle of the craptastic eBay wings

[joshh]

You mentioned not having played with rear tire pressures. That's where I'd think to start. It may not solve your issue altogether but in the rain tire pressures are vastly different than in the dry. Take 5 pounds out see what happens.

[Jparkr]

You mentioned not having played with rear tire pressures. That's where I'd think to start. It may not solve your issue altogether but in the rain tire pressures are vastly different than in the dry. Take 5 pounds out see what happens.

We started with 30#
Five # were removed when I got out of the car and James got in, It helped a little. The weight helped the most. A little more down force and the car may be as good as we can get it to be in wet conditions.

[CorvallisBMW]

You're counting that wing in the budget, right? *cough*cheaters*cough* :)

My car hasn't had a huge need for downforce, but then again we haven't exactly been breaking any speed records with an eta motor. Will see if things change with an M50 under the hood. Maybe the fins are the key?

Wow, and I thought our motor swap was going to raise eyebrows ;)

[BlackbirdM3]

Simple solution... What e30 won a World Touring Car championship? Oh yeah that would be an M3... The rear spoiler of an M3 with a DTM gurney flap would work wonders. Now, you guys have a couple stikes against you, one you lack the step on the roof for the M3 rear window and C pillar. You might be able to fake it by using a piece of clear plastic wall edging mounted in aproxamatley the same place. This will cause the air to trip and fall down over the trunk lid. Your missing rear window is going to screw this up horribly. You can get an idea of what the air is doing back there by mounting a go pro camera looking back at the trunk and attaching some long pieces of yarn and mounting the fronts of them on the front wind shield and letting them fly back over the back of the car, and then off the back of the car. Take the car for a spin and see what the yarn does. You might want to mount the camera in a few different places as well as moving the yarn around. You will want to use several different sizes so you can see whats going on. If the strings are too long they won't work. We played around with this on our Lemons car (former TRON, now Flailing Lizards Ford ZX2 Escort.) We have played around with this, and we did get the car to handle better.

Back to making a fake M3 spoiler. You need the step in the roof to get the air to flow down onto the trunk and then over the spoiler mounted there. When I drive my M3 in the rain, I've gone 150 miles with rain water on my rear window, that air there doesn't move, its totally still. In some areas I've seen water droplets moving up the rear window toward the roof. That means the air is flowing well aft of the rear window and is going over the rear spoiler (I can see it in the rear view mirror.) Since you don't have a rear window, it might do odd things. (Back to using the yarn to see what the air is doing.)

If you guys are clever, I bet you could rig something up like the proven M3 spoiler. You can even add a big or bigger gurney flap off the spoiler for more downforce. Heck you get it right and you might be able to find a few more seconds per lap on top of having a good handling car.

If you are going to run a locker rear end, learn how to drive one. Its not like a LSD. On throttle it should keep things under control, off throttle it will rotate, and in the rain its just not a good idea what so ever. I run a Detroit Locker on my Datsun, in the rain its so much of a handful that I'd rather walk to work.

Will

[Jparkr]

Good advise. This is making me wonder about using no rear windows to our advantage.

We may be able to level the rear deck area to the same height as the trunk lid. Then use some light fins to direct air into the rear 1/4 panel windows and funnel it directly out the rear window area. Land it directly onto a shorter wing...

Any engineers see any holes in this plan?

[NigelStu]

^Yes.

There will still be a lot of turbulence off of the back edge of the roof, at the leading edge of the side windows and around the c-pillars. The 'dirty' air won't do that much on a small spoiler. At best, I would expect any downforce created on a small spoiler by trying to direct the air would be balanced out by drag/llift from the roof.


One thing that isn't clear to me yet is what types of corners you guys are having the most issues with? Low speed or high speed? If its coming out of slow corners (2nd/3rd gear), aero isn't going to do much at all - at those speeds its all about mechanical grip (unless you go ridiculous like the AMod car).

If its high speed stability issues, I would think a big factor would be lift that is being generated due to no rear windows. Adding rear windows would be a big step in the right direction, and more effective than just adding a spoiler/wing.


Side note, time/cost for adding rear windows is likely lower than winglets and spoilers. If you are interested, I still have the 3 piece set of poly WDWs available (2nd set I made from the 4x8 sheet I bought) or I could be persuaded to finally find a roll of poster board and make up some templates (then it would be up to you guys to local-source polycarbonate)

[kamotors]

The M3's trunk also sits higher which I would guess helps get the spoiler closer to roof level than a regular E30. On my Subaru I have a E30 M3 inspired wing with the gurney flap. At speeds as low as 60mph in the rain or snow you can actually see that its creating a spiral on my trunk lid(similar to the bed of a truck);water and snow will both crawl up my rear window. I would think that something with a gurney flap would help you out but then again you have to rear window... Testing would need to be done like stated before.

[BlackbirdM3]

The piece of angled plastic on the roof would move the airflow back and down, just like the vortex generators that you see on Mitsubishi Evos and some of the later M3s. That part is that makes the rear M3/Mitsubishi spoilers work. Do some searching on google to find out more. Do put the rear windows back in. Even if they are lexan (less weight) you need those there to get the aero dynamics to work.

The addition of the e30 M3 rear window assembly lowered the coefficent of drag from something like .38 to .33 with much greater stability over the original E30 body. The parts aren't there just to look cool, they really do make a difference.

Will

[Jparkr]

^Yes.

There will still be a lot of turbulence off of the back edge of the roof, at the leading edge of the side windows and around the c-pillars. The 'dirty' air won't do that much on a small spoiler. At best, I would expect any downforce created on a small spoiler by trying to direct the air would be balanced out by drag/llift from the roof.


One thing that isn't clear to me yet is what types of corners you guys are having the most issues with? Low speed or high speed? If its coming out of slow corners (2nd/3rd gear), aero isn't going to do much at all - at those speeds its all about mechanical grip (unless you go ridiculous like the AMod car).

If its high speed stability issues, I would think a big factor would be lift that is being generated due to no rear windows. Adding rear windows would be a big step in the right direction, and more effective than just adding a spoiler/wing.


Side note, time/cost for adding rear windows is likely lower than winglets and spoilers. If you are interested, I still have the 3 piece set of poly WDWs available (2nd set I made from the 4x8 sheet I bought) or I could be persuaded to finally find a roll of poster board and make up some templates (then it would be up to you guys to local-source polycarbonate)

High speed, Turn's 4, 5 and 6 (w/chicane) at Portland Top of third gear with the 4:10 and the M30


Lots of good idea's everyone thanks. I think we will re-install windows first and feel it out since that is the cheapest option.

[Nsquared97]

The addition of the e30 M3 rear window assembly lowered the coefficent of drag from something like .38 to .33 with much greater stability over the original E30 body. The parts aren't there just to look cool, they really do make a difference.

Will

Good to know, I never understood why they went to the effort to change all of that. Espicially when I don't think it looks all that great.

[CorvallisBMW]

I'll have to check the rules regarding windows, I'm not sure if we can have them.

EDIT: windows are not allowed in Chump, we would have to fab them out of Lexan/polycarbonate

[dinanm3atl]

Currently the weight distribution must be in the order of 60/40 or worse. With an m30 hanging over the front axle, a completely stripped car and even the spare tire well removed from the back, it's a disaster. This last weekend we put 2 bottlecaps w/ tires in the trunk, strapped them down and raced the 2nd day with some ballast and noticed a marked improvement in handling.

Dry handling isn't too bad, it's when things get wet that we have our biggest issues. Drivers are saying that even breathing on the gas pedal mid-corner will cause the back end to step out of line like a teenager on heroin. We don't dare touch full throttle unless going dead-straight and deep in to 3rd gear. The back end just won't stay planted. Current suspension setup includes:

FRONT
unknown front springs (Dinan?) with unknown shocks
M3 CABs
stock front swaybar/bushings

REAR
no sway bar
4.10LSD or 3.73 welded
urethane subframe, RTABs and diff mount
H&R cup kit springs
bilstein sport shocks
weld-in RTAB camber/toe adjusters planned before next race

We haven't played much with tire pressures and generally start around 28psi cold and hit 32-33 on cooler tracks or with rain. We didn't bother with taking temps as it was raining, and that's when we have our biggest issues. With all the power this car makes I don't mind loosing some top-end speed in exchange for downforce in the corners.

Wowsers. How do you have all of that stuff and keep it legal? Plus the M30?

You're counting that wing in the budget, right? *cough*cheaters*cough* :)

My car hasn't had a huge need for downforce, but then again we haven't exactly been breaking any speed records with an eta motor. Will see if things change with an M50 under the hood. Maybe the fins are the key?

This is one place the series is getting a little out of control. 24V E30s have E36 m3 speeds in the straights...

I'll have to check the rules regarding windows, I'm not sure if we can have them.

As I understand you could add lexan back to the car.

[BlackbirdM3]

When it comes to aerodynamics on an E30 platform, all one has to do is look at the M3. Had BMW thought that there was nothing more to be gained from the stock E30 platform, they wouldn't have made all the changes (aside from the fender flares) to the car. Remember, they build the M3 for one purpose and only one, to go win at top level touring car championships. The car evolved as they went as well. The EVO1 was pretty much a straight up M3, the Evo2 gained the front airdam, and the little spoiler below the larger usual spoiler, then with the Evo3/Sport Evolution, the front airdam went back to near stock and the adjustable splitter was added. In the back the spoiler went from the Evo2 setup to the Evo3 adjustable setup with different sized flaps.

Yes, the trunkline is a little higher, and uses a Kamm tail. With a little creativity, you could do the same . Seriously, borrow all you can from the M3 for aerodynamics, they aren't there just to look cool. BMW spent lots of time in a wind tunnel to make the cars as fast as they could possibly be.

Just a thought,
Will

[CorvallisBMW]

Oh I understand what made the M3 great, but this is a $500 racecar not a $500,000 factory-backed touring car. We don't have the $ to graft on an entire M3 rear end. Hell we don't even have a back window. Some things can be easily done, like leveling out the rear shelf to be even with the trunk lid, adding some small vertical fins to help smooth/direct airflow and adding a wing/spoiler, but beyond that we're risking so many penalty laps (ya, all this stuff counts) that it would be totally counterproductive.

Like I said. wing vs spoiler. That's really all I care about.

[dinanm3atl]

How low is your AIV to start to add urethane bushings, sport shocks, springs and a motor swap? It must be pretty darn low so the wing shouldn't be too bad. There was an MR2 with a V6 camry swap, Replica APR wing and a wooden front splitter at Road Atlanta. Did a 1.46.XXX