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Splitter idea

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really like the looks of it, very cool with the side pipes.


I was looking at this universal splitter. Used on quite a few cars from the sounds of it. Someone was posting that they even got banned from using it. Looks like it could work with some minor modifications. I like the channels that are built into it similar to how @Heavy85 had his in page 3.











Edited by AZGhost623
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Yes, that would be good if it fit, but the diffusers would make it illegal for lots of different racing categories, including mine (X Prepared). Another option is the NASCAR COT splitters. I bought one and it was too narrow for my car, but essentially it is just the front lip and a little more, probably 10 or 12" deep, then you could do your own diffusers on the backside if you wanted, or just run it back to the x member.


Just to update on my splitter, I found that the turnbuckles were too long even at the shortest setting, so now I'm thinking I'll make different length supports so that I can move the splitter down in 1/2" increments. Thinking of just pinching the ends of some -8 fuel line that I have and screwing that to the splitter and the dam.

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I've built (only in my head) an airdam that is mounted on drawer glides, with travel stops at the bottom, that would allow it to rise and fall as it skimmed along the ground. With maybe replaceable white plastic skid pads on the bottom.


The problem with my splitter was that, even dropping straight down off the front of the hood, and racing on a fairly smooth and level track, it kissed the ground several times. I think it has to do with the distance that the leading edge is in front of the wheels. Starting 3" off the ground, I never would have dreamed that it would kiss the ground, but it did. And it wasn't from downforce: when I cut the splitter/lip off, it STILL kissed the ground. And loading it on the trailer with it installed was a no-go. The 3" splitter I built was fine without supports to the airdam (the paint and resin showed no sign of flexing). I'm confident the scraping was due to suspension bump travel (possibly) aggravated by downforce. For next season I am doubling spring rate, putting the splitter back on, and trying again.




Edited by RebekahsZ
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I think the sliding air dam is a potentially dangerous idea. If it's doing its job and making a bunch of downforce and then it loses contact, or if it hits a bump in the road and fails (on one side even), you're going to have a real issue. I know it's apples and oranges, but as I recall one of the main reasons that ground effects was banned in F1 was their sliding fences which maintained contact with the ground failed, causing a sudden lack of downforce and big crashes. Still, if you're going 170 mph, your risk tolerance should be adjusted to match the new conditions. 

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  • 6 years later...

I've had two Z cars with splitters in the past. Both were faster with them than without them, and neither had any issues with porpoising. We generate significantly less downforce than a sports racer with a flat bottom and front and rear diffuser sections.

Based on my previous experience, I believe your idea will work, but I'm not sure I'd put too much effort into it. You can't run a diffuser section on the splitter in either XP or EM, which would see this  how to  increase the pressure gradient and cause the bouncing.

I would suggest that you make the splitter hinged and able to move up when it comes check contact with the ground. This will save a lot of wear and tear.

Edited by nicholasjackson2
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Guessing he found it when he was searching for "splitter."

FWIW I ended up making one out of plywood. Didn't want to do it from CF and then break it immediately. Kinda glad I did. It has rubbed once or twice. ;)

I've been autocrossing with a club that has 3 classes: FWD, AWD, and RWD. Since the rules are wide open I've been thinking again about doing diffusers and all of that. Have a couple other projects going though, so nothing planned for the immediate future.


Edited by JMortensen
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Gosh I have been debating 6061AL sheet or plywood. I’m only allowed from leading edge (air dam) to the front of my wheel well arch’s. Not a whole lot of length, but I’m certain it’s a critical addition. 

Jon is your plywood a standard 3/4” section? I don’t recall other standard thicknesses, but maybe 3/8” is available? The Russian birch plywood is 10mm and stiff as hell. Was thinking about that… 


If I do it in AL sheet, it will certainly need some stiffening. I don’t want extra load on the fiberglass dam, so I was thinking of some cantilevered supports (attached to the lower rad mount crossmember) but it will take some thought 🤔


also, do you run a flexible skirt on the leading edge of your dam? Greg uses one (pic attached) but might not be critical for the slower speeds of autoX. This piece is a “consumable”, since it is bound to make contact with the pavement. 


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I'd personally do plywood until you get the design all figured out.  It's cheap and easy to work with.  When you want to go all out you can route out big sections and use foam to fill them in.  Then put some Kevlar on the bottom and some carbon or s-glass  on the top and you'll have a very strong splitter.  For the splitter frame make it adjustable and sprung so it can move up if the car gets too low.  I see a lot of solid mounted splitters that people grind off.  Done right you can make this a performance adjustment but that may get you in trouble with the rules.


Leading edge treatment (flexible skirt or radius) depend a lot on what the rest of the car has going on underneath.  If you have mostly a flat floor and not anything hanging down to act as a sail them you want air to go under the splitter.  This helps to reduce pressure and leads to higher downforce numbers.


If you don't have a flat floor or there's a lot of stuff to catch the air then you are better off blocking it off and using the edge like in Greg's pic above.  Either way seal off as much as you can under the car and back to the wheel center line.  And if you can exhaust the radiator into the fenders (assuming you can do hood vents) and add some s-flaps that are adjustable. 


Hope that helps,


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Very helpful Cary! The sprung splitter was great idea! Il give the 10mm birch plywood a shot. I feel the standard 3/4” cross section (sometimes sold as 4/4) is too thick and heavy.


The EP rules are quite restrictive. No new openings between fender and engine bay. No non OEM hood or body vents. Splitter must stop at leading edge of wheel well opening. Explains why Greg uses what I’ll describe as a “skimming” skirt since we can’t blind-off the bottom of the car beyond the front. 

Still… rules help to keep my budget down 😂. Unless you are a magician with a fuel cell there is a ton of Eddy movement behind the rear skirt. I might attempt to block it off with some 0.032 6061 AL, but my gut tells me the officials will notice it. Heck even my new fancy fender nose cones are illegal 😕. Should have assumed Greg’s EP car didn’t have them for a reason! His CP tribute cars all do though. It was just so tempting to shave all that weight off the leaving edge. The 3.5lb setrab oil cooler was a hit in the wrong direction (but we’ll worth it!). 

even my fancy engine-to-cowl vent relief is likely illegal. At least on that I can simply blind it off with 20-gauge steel. 




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Yes, I did run a skirt. I have it set up on a pivot on the back and was going to run cables in the front, but as it turned out it didn't allow for much movement when installed and there was some other problem I can't quite remember so I ended up using AL fuel line smashed on the ends to make struts for it. Passes the "stand on it" test. 1/2" birch. 3/4 would be really heavy.

I just went to Home Depot and found a flexible white plastic that I think is used behind showers or something like that to waterproof. Easy to trim to fit. Have a small 1/2" AL angle section on the splitter, and then it's screwed right to the fiberglass. It looked pretty nice before I drove it, but after the splitter hit a couple times the plastic warped and buckled. Oh well. Race car.



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Oh wait. You meant a skirt at the front of the splitter. I had that idea about 10 years ago and emailed Simon McBeath and he wrote me back and said don't. Also emailed Glenn Bunch with the road race Challenger, because he had pics of his on the track with a splitter with a dam on it, he gave it a thumbs down. I shared all of that in page 2 of this thread.

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