This is a great thread, except of course all the smart asses hat don't have anything else to do. I was thinking of building a splitter myself, totally over-thing it. but this has given me some great ideas.

 

everyone with a splitter has lip. is that necessary to get the splitter near the ground or could you do it without the lip?

 

Not totally necessary but it will be more effective closer to the ground. The pressure differential as discussed earlier is key. If the gap between the bottom of the splitter and the ground is larger (splitter raised higher up) then the flow under the splitter will not be as fast and thus less pressure drop. This means less pressure differential creating downforce.

There is a point at which it is too close to the ground and the performance drops off. But, based on what I have seen, this point is so low the splitter would not be practical for anything but a smooth race course.

 

Try the stiffness of about .020 aluminum sheet glued to both sides of 1/4 inch plywood.

This sort of stuff has put a lot of performance into small airplanes.

The crazy Brits have built both airplanes and cars from plywood. Bundy is spot on, cheap, light, stiff, and a piece of cake to form.

Corky

 

i don't run a lip with my splitter. i did make an air dam but it seemed to slow me down alot on long high speed straights. so i just run the splitter and have my car lowered.


with the air dam:



without:





you can see the 2 points that hold on each side, and i have gone off under braking, over the curbing and scouped some heavy georgia clay, and it bent the aluminum down, but didn't even come close to ripping it off the car. also not sure how it could possibly hurt my radiator. most of the splitter is under the car, only a tiny portion sticks out ahead of the bumper, and it's alum. so it won't tear off and go flying thru the rad. if it did rip off i would just run over it. although i did try to stomp it off and it didn't budge.

 

How far back does a functional splitter have to go?

A few google searches got me to the conclusion that to the steering rack and beyond, steering racking being a "minimum" point that a functional splitter should go.

Edit: How far in front of the bumper is "ideal"

 

^).

 

A splitter + aluminum beatrush undertray combo works really well. Pretty much downforce and a smooth area extended all the way back to the tranny.

 

I think it's basically as far out as you can go and still have it be supported. My first splitter was 5-6" out, and I think my current one is around 4", but I changed bumpers so the 4" splitter is actually larger than the old one. It's the same theory as big endplates - the bigger it is, the better everything works.

 

Sav at speed, say in high speed corners, is your front splitter downforce balanced well enough with the rear wing downforce? I need to build a splitter and I am trying to decide how large to make it. I have an APR GTII wing which is supposed to be close to the one you are running.

One of the tracks I will be running at has some long fast turns. So if there is a downforce 'imbalance' I would think shifting from understeer to oversteer (or vice versa) as a function of speed would not be ideal. Or maybe I am overthinking this I suppose I could build a large splitter and 'tune' the balance with the AOA settings on the wing.

No downforce aero tuning with motorcycle road racing so I am learning about this aspect of the game.

 

I made mine stick out 3" from a GV style lip spoiler. Probably 5-1/2” from a factory lip I settled on 10mm thick ply and a single layer of fiberglass top and bottom. It is stiff as hell and weighs 9 lbs. not quite finished yet.

I have an APR GTC200 wing but it is a Universal fit one as I got it for $250. I have 2 sets of the 2.5” risers for it. After finally biting the bullet and drilling holes in my trunk lid to mount it then seeing how difficult it was going to be to make the trunk lid stiff enough I am changing my mounting. I found a couple of 1.5” X 1/8” aluminum angles slip in the gap between the trunk lid and the fender. I can use the wider mounting holes on the wing and mount it to the fender right in the trunk lid gap. Much more rigid and not pushing down on a rubber mounted trunk. With the 5” of riser I’m using I can still open the trunk enough to make it sort of usable. Best of all it is much easier to take the wing off and it leaves no mounting marks on the car. The only problem is I wish I would have figured out this mounting before I drilled 8 holes in my trunk lid that has an expensive lip spoiler bonded to it.

More pictures to come when I get a chance to take some also no data yet on how it performs.

Bob

 

well i don't know what a difference one going further back than mine would make, but i can tell you that mine makes a huge difference even at highway speeds. everyone can read about theory all they want, but i know what mine has done to high speed stability and it doesn't go that far back. sure i'd love to panel off my whole underbody, but i think there's other things i can work on right now to pick-up what i'm leaving on the table.

zx-tex, i ran a splitter without a wing for atleast 6mos. and 6-7 events including tws and there were NO ill effects. my car didn't oversteer at all because of it, it just felt 1,000x more stabil at speed. the steering no longer needed correction. the wing when i added it, just made it feel awesome at high speed braking and trailbraking. (like when running tws cw and turning off the banking under breaking into the chicane) yes you are over thinking it. just build it. 2.5-3'' is usually plenty as far as splitter length past bumper, (plus if i go any further i have to add another point for time trial classing)
so apparently, more is better unless you also drive the car on the street or are points limited. (like i am)

 

OK that is good info. TWS is the track I had in mind as far as high-speed turns. So for the TT points, are you talking about NASA? I'll have to re-read the rules as I plan on eventually racing this car in NASA TT. I ran through the worksheet once but do not remember the splitter length part, but that does not mean it is not there.

 

As far as I understand from my conversation with Greg here in socal NASA Your car is classed off your P/W ratio and then point assesment. I am looking at running TTC next year at 12:1 ratio. My understanding is that you can do what you want as long as you fall under the P/W ratio of the class and don't go over the points for the adittion of parts to your car. I may be wrong, but that was my understanding.

Have a great day,
Jared

 

This is what I do. I adjust the AOA at every track I go to. Less wing at Calspeed where I need to get to top speed quickly, and more wing at places like Laguna where the entire track is 3rd and 4th gear 90 degree corners, and I need to hook up all the power I can at all costs. On most tracks, I will set the car up to push very slightly on aero, and then compensate by getting into the power sooner.

I wouldn't use a splitter without a wing, at least not a big one. Nick drove my car at MRLS with a splitter and no wing, and he said it was scary going over the hump on the front stretch at 115-120mph. The rear end would get EXTREMELY light. Definitely noticed the change in the car's attitude.

 

my friend has a 1/2" plywood splitter on his focus for redline time attack and he jumps on it lol

 

spoolin2bars,

yours looks great, I was wondering if you had to have an air dam to run w/ a splitter. Case closed, strong and simple, can't get better than that.

 

Great! Glad that approach works.

Glad you brought this up; that is another thing I was wondering about. Set it up for very slight understeer, and correct with the throttle as needed.

Also good to know. I am putting the wing on first already so there is no chance I will have a splitter and no wing.

 

Keep in mind that you need a lot of power and a lot of confidence on the brakes to make this work. The aero push will make the car not want to turn in, so you have to trailbrake a bit more to rotate the car. Once it's rotated, it will want to un-rotate itself so you have to pick up the throttle pretty quickly and be sure the rear end stays a little bit lively. If it hooks up, and you don't have the power to get it unhooked again, you're in trouble. It forces you to be on the throttle earlier, which is probably the single hardest thing to learn to do in a high-horsepower car.

 

completly off subject. but Savington drops track knowledge everywhere i see him post. thanks for the usefull information.