SDIF

Anyone made a rear lexan spoiler. This is not for a car show, but the race track. I figure 10 inch high at 45 deg angle is a trial starting point.

Give me some ideas on mounting.

Sonix

iTrader: (1)

i'm curious, why lexan? You *want* it translucent? If not, I would go with something less dense. That stuff is actually pretty heavy.

SDIF

I need to see.

WheelsUp84z

iTrader: (2)

is this for a drag car or a circle track car???? 45* angle is deffinately makeing more drag to the amount of downforce it will produce. i cant see you needing more than 10-15* MAX elevation, not to mention you probably wont need it nor will it help you unless you're in the single digits. circle track is different, but you'll be in the same boat for calculations for the drag/downforce compensation. spoiler kits come premade and are made of sheetmetal, thats a good starting point to get some ideas, or you can just buy one thats already pre-formed for your application

SDIF

Application is road race.

Max Speed on current track about 137 @7000 in 4th gear. Rear end gets loose in fast turns 90 to 120 mph.

I have to slow down too much. Hense the need. If it kills top end I may be better off on average speed and lower lap times.

What angle to you recommend?

Where do I find pre made kits??

AlkyIROC

Drag cars use aluminum and go flat off the back. They don't need as much down force as an oval track car that's going around corners at high speed. I don't even have an aftermarket rear spoiler on my car. I still use the Z28 factory 3 piece one.

Ed Quay makes hardcore race parts for third gens. www.edquay.com

Axoid

One of the supporting venders on FRRAX.com makes them for 4th gens and was doing a GP on them last year. I talked to him about one for a 3rd gen and he said he could do it, but I hasn't been high enough on my list to go forward with it.

BlueBeast

why dont you try the hawks 5 inch spolier?

bluethunder28

iTrader: (1)

I made one using the stock spoiler and in the process of making another one. You just bolt the lexan to the spoiler. That's what most racers do

5678TA

137@7000?!?!?!?! jeez... i think you should swap those 4.11's for 3.73's.. your motor will live a little longer..

SDIF

I made one using the stock spoiler and in the process of making another one. You just bolt the lexan to the spoiler. That's what most racers do.

I could try that. That sounds simple enough. It looks like it may try to rip the stock spoiler off.

What speeds were you runing and what was the effect?

GMan 3MT

iTrader: (4)

Yup, adjustable and pimp looking too. A buddy of mine got one for his vette...
http://www.mowhineracing.com/ch8.html

I'ld love to buy the Hawks 5", factory looking and I'm sure functional. Tho for 300$, I'ld rather buy the one above and have it adjustable.

But I'm cheap/broke. Anyone have the pictures of the spoilers bolted to the factory spoilers? I considered this but didn't think there was enough space in the void beneath the spoiler.

bluethunder28

iTrader: (1)

It was used on a CMC road racer for about 3 years before it broke. It held the rear down pretty good in the turns. I will be using thicker (3/16) lexan this time around.

Thestriped1

the vet spoiler looks like it will work more like a parachutte then a spoiler. If you could make one electronically adjustable then you could stop the spoiler from creating drag on high speed straight aways.

I'd say if you haven't already get wider rear tires, more rubber=more traction
and it'll probly help more than a spoiler will. Extra rear end weight will also do a good amount for you if its directly over the tires.

SDIF

"the vet spoiler looks like it will work more like a parachutte then a spoiler. If you could make one electronically adjustable then you could stop the spoiler from creating drag on high speed straight aways.

I'd say if you haven't already get wider rear tires, more rubber=more traction
and it'll probly help more than a spoiler will. Extra rear end weight will also do a good amount for you if its directly over the tires."

Drive adjustable spoilers are not legal in my class or any class that I am aware of. The reason is if they fail you fail, but I like the way that you think.

I run the widest tires allowed by the rules,

I am trying to use the aero in liu of the extra weight.

V8Rumble

iTrader: (2)

OK, a few people here (and anyone who checks out my vBGarage) know that I'm very strongly interested in running my GTA on the salt at Bonneville. As part of that, I've been doing a lot of studying of aerodynamics, & I can tell you guys that (no offense!)...

Some of the people in this thread are really over-thinking the issue.

There's no need for a huge spoiler, or 6 square feet of aluminum hanging off the rear of the car - and God forbid that anyone run a sharp angle like a 45*! (BTW, the spoiler on the 'Vette is ridiculously angled, almost r!cer-like - it's hurting him a lot more than helping.)

To address the original question in this thread, I'd say that the "elegant solution" for the problem you've posed is the "Gurney flap" - it's small, so it doesn't block visibility, doesn't weigh much, and it provides downforce all out of proportion to it's size. To make it nearly perfect, it doesn't even cause much drag on the top end!

Give that a try, if it doesn't help, come back here & we'll see if we can figure out what will.

Good luck, I hope this helps.

Axoid

That is where the difference is use comes in.

In autocross (where that Vette is run) where the top speed is 60-70 mph you need ten inch spoilers set at hard angles to get any down force at all. On a road course with a top speeds of 130-140 mph you'd want a lot less spoiler, maybe five inches or less set at a softer angle.

On the salt flats you'd wouldn't much of any spoiler, just enough to keep the car stable. A salt flats aero setup would be useless on a autocross course just as the Vette's would be like a parachute on the flats.

V8Rumble

iTrader: (2)

OK, I didn't see that the 'Vette was being used for AX, given that, it may not be as bad as I initially figured. You're right, less speed == significantly less aero effect...

Thestriped1

I dont know your resources or how much coin your willing to drop in order to win. Now knowing that you have the biggest tires and dont want to add weight you can trade wight or change your body's styling a little bit. You can change the rear glass to a much lighter material than glass or you can get a fiberglass notch back. at higher speeds the notch back actually helps push the car and creates downforce over the rear tires. If you dont know, a vaccum is created by the sudden drop in the rear. whle the hatch back is designed for to be a large smooth surface for air to run off of and graze a small spoiler that is pretty much ineffective at most speeds, the notch back creates a vortex that swirls behind the vehcile and accual pushes against the rear of the car and pushing the back end down and slightly adding to the propulsion of the vehicle. dont expect great speed gains but you MIGHT see t better your mpg slightly. If you can try to get your ride into a wind tunnel you can see what im talking about. or your can try to download an episode of mythbusters where they build a small modle with a toy pickup truck and they show the vortex's exsistance using water current instead of air current because more stuff can be suspended in water to show it. also try reading a few articles about air flow

SDIF

Like Axoid said... I need more rear grip at low speeds.

Al Miles

The March 2007 "Hot Rod" has a feature on page 112 titled "Wind Camp" which provides some very good information on aerodynamics. The C/D (coefficient of drag) and the C/L (coefficient of lift) do not change for a given shape, it is the amount of force that changes with velocity. Granted, there is not a lot to be gained at lower speeds, but a properly designed aero package provides gains in down force and fuel mileage (less power to go the same speed) at all velocities.

Al Miles

pizza_guy

Yeah, a vaccum is created, but the truth in that post ends there.

Since when does a vaccum push?? I seriously think you need to sit back, read, and learn a few things.

Thestriped1

the vaccum creates a vortex and as it was expalined to me this vortex's spin pushes the rear end down at high speeds and pushes against the rear of the car.
Now that Im thinking about it the notchback will also lower the center of gravity slightly, but in a race at those speeds that little bit matters a little more.
I dont know the exact dimensions of the notchback but based upon the dimension the vortex may or may not push angaist the rear in a foward direction. Theres a lot of math involved and im going to leave it up o you to do those equations if your seriously interested about the notchback.

as for pizza guy...stick to pizza because you abivously dont understand that a vaccum is a void of air and based on proven scientific principles you'll find that air will try to fill this void, the air then swirls back and if dimensions are correct it WILL press down on the rear or possibly push from behind against the rear of the car. Dont try to lecture people when you obviously dont know what your saying.

Julie Bergman

Here's a pic of the Blaine Fabrication spoiler on my CMC 4th gen. He's the FRRAX vendor mentioned above. It is great to race with!

SDIF

Julie, thanks for the nice picture and your sincere desire to help.

I find this board more helpful than the NASA forums.

I planned to run AI this year, but have been placed in AIX due to lack of a Dyno certification. I have not had the opportunity to get the car to a chassis dyno yet. I ran a Porsche 930 in NASA's GTSU last year and have been track daying my 3rd gen street car for 5 years.

I am going to fabricate something similar to what your car has. I could buy one perhaps, but that takes away all the fun!

Thanks again to all for their help. If I had all the answers I would not have asked the questions.

Julie Bergman

Glad to help another racer! Besides, we gotta beat them F*rds!

GMan 3MT

iTrader: (4)

Wow, similar to the 1966 Chaparral 2E? (except that wasn't done electronically) If Can Am banned it, I'm sure every other race organization doesn't allow it.

So the vacuum only pulls air to fill the void and doesn't "pull" the back of the car too?

Before you start to bash people, I'ld like to see some of these scientific principles you speak of. I'll submit my 5 second search for you to read... http://en.wikipedia.org/wiki/Spoiler_%28automotive%29

Back on topic... Juilie, didn't Alan suggest an 8" (and that's what you're looks like) for road racing and a 10" for AX?

As for my buddy in the vette, he does run DE in that car at Texas World Speedway. He was fixing a very loose condition. He may have reduced the angle, but since you're mostly turning during a lap, I'm sure he sacrificed a little staitaway speed for cornering downforce.

SDIF

Update,

Added 10 inch spoiler at 45 deg. It is attached to end plates welded to tops of qtr panels and the angle can be adjusted.

I tested the car this past weekend. Added spoiler no other chages.

Track Conditions
Greasy, very Greasy not as favorable as when I tested before.

Results
Top speed was reduced by 300 to 400 rpms

Lap time reduced by 2 full seconds.

Corner exit speed was up significantly!!!!!!! Car would 4 wheel drift for the first time.

Conclusion... It worked.

GMan 3MT

iTrader: (4)

Get any pictures?
Awesome!

askulte

SDIF - There's quite a few folks on the www.frrax.com forums running Alan Blaine's lexan spoilers, with plenty of pictures, if you need ideas. I'm planning on running a wing in the rear and splitter up front, and based on the airfoil shape (Javafoil is great for getting CL data at various angles of attack, and free) at 100 mph, I should see about 400 lbs total downforce, which is good for another .1g cornering.

Edit - I just read your last post. Glad to see it worked well!