Downforce needed - battle of the craptastic eBay wings

[priapism]

Moving Cessna wing

[Massimo]

^
lol

[Nsquared97]

Just throw one of these on it and you'll be golden...

[priapism]

What? When do you have the hardest time putting down power? 2nd, and maybe 3rd, so by running the servo opposite the speed sensor you're going to have most downforce when you're going slow. Which is coincidentally the hardest time to put down power.

Sorry, I thought you had it backwards.

[CorvallisBMW]

It's hard to comment on the welded diff since he haven't run it in the rain in over a year and back then we had a very different car. for now we run it only in the dry.

The front springs are definitely stiffer than the rear but those H&R cups are very soft and quite low. We don't really have rake.

The team has talked about some second-hand IE Stage III springs. Weight in the rear is also a good bet; we're thinking 50-100 lbs centered right above the rear axle centerline

[NigelStu]

Unknowns create unknowns ;)

Not sure how much aero will help, based your your description. Is there any difference between the LSD and welded diff? I'm going to guess in the wet the welded is a handful....

Sounds like (other than the obvious weight distribution aspect, which directly impact balance) the front to rear wheel-rate balance is off, with % of balance being too high in the rear.

My suggestions:
If you can, measure the front spring rates and compare against the H&R cup front spring rates. If they are softer, than H&R cup front spring rate, I would try to source some proper spring rates for the front - with the weight balance, I'd say front rate should be higher than the H&R cups. You could also try reducing rake (even go negative rake if you need to) - add shims/spacers up front, take out the rubber shims in back if they are there. See what else you can pull off the front of the car to reduce weight up there. And get some lead for the rear to help even out the distribution; extra weight should be balanced out with more time spent at 100% throttle.

[CorvallisBMW]

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.

[NigelStu]

idea for super-cheap NASCAR style spoiler - assuming you have a parts car with a crappy trunk lid... cut trunk lid ~3 inches from the back edge, discard the front portion. Flip over and place at back end of trunk lid on the car. Bolt in place.

[NigelStu]

What kind of situations or where on the track are you having power-delivery issues? e.g., what type of corner (high-speed sweeper, low-speed with heavy re-accel, High lateral-g turn), and when during the corner is the problem occurring? How and when does the issue present itself?

Also, what's your FR/RR weight balance? Any idea what condition your RR diff is in? RR sway bar? Just trying to get an idea if suspension tuning (making both rear tires work better) could have more impact than adding aero alone.

I know its Chump, but if you are already thinking about finding a way to make active-aero (sweet idea, btw!), then I'd expect you'd have no issues with being able to fine-tune damping / spring rates / roll-rates.

[alane]

That wouldn't help him put down power, which was the point of the thread.

What? When do you have the hardest time putting down power? 2nd, and maybe 3rd, so by running the servo opposite the speed sensor you're going to have most downforce when you're going slow. Which is coincidentally the hardest time to put down power.

OP, if you're having a ton of oversteer coming out of corners, downforce will help but proper spring and dampening may be something else to look at. Do you take tire temps?

[priapism]

If you run the servo opposite the speed sensor then you'll have downforce at lower speed and it will even out at top speed. If you can do this and also run it off the brake light switch so it goes into max downforce on the brakes that would be optimum.

That wouldn't help him put down power, which was the point of the thread.

[alane]

That would just limit your top speed. You want it linked to lateral Gs.

If you run the servo opposite the speed sensor then you'll have downforce at lower speed and it will even out at top speed. If you can do this and also run it off the brake light switch so it goes into max downforce on the brakes that would be optimum.

[priapism]

That would just limit your top speed. You want it linked to lateral Gs.

[CorvallisBMW]

^ we've been toying with the idea of an adjustable wing. Tie it in to the speed sensor :twisted:

[priapism]

Check out the setup POS made. They rigged a pimptastic ricer wing to a windshield washer motor. There's a button on the steering wheel, so when they go into a corner they hit the button and it goes up, come out of the corner and it goes down. Caswell said it made a huge difference in how that car puts power down.