rithsleeper

I've been looking into starting this project, and there are tons of c5 and c6 guys who have them. Not many c4. Unfortunately they all look super lame on a c4. What I would consider the most successful c5 homemade splitter still looks like it is at least 5-6 inches off the ground.

I've seen some dp cars in real life that are slammed on the ground. I figure I need about 4 inch clearance to clear kinks and that big hump at road Atlanta at the top of turn 3.

If I make covers under the car to seal it all off does it really need to be super low? How good does it have to be at moving the air above it either through the rad or to the side of the car. I'd say my front air dam is pretty far back and I would just extend it down to the splitter but I doubt it would be practical to extend the splitter out past the front of the bumper due to the c4 nose shape. Is it absolutely necessary?

Or would this just create a huge high pressure pocket that would drag like crazy? Big sideways u shape under the front to catch air?

Also do you think sealing off the bottom would require more air escape than just my gills? I potentally could buy junkyard gills to replace my stock ones and cut them out a lot to open them up for the increased flow....

Lots of questions. Hope they make sense.

rfn026

Last year I worked with a Nationwide team. They couldn't used data loggers on the weekends so they became experts at reading splitter wear. Splitter wear was an indication of how the car was handling.

Back to your question. You want the splitter low enough to rub on the track. You don't want it so low that you break it though. You need to find that magic spot.

Richard Newton
Historic Racing Images

ratt_finkel

I'm not sure what you mean by covers. Or what you plan to seal off. But whether you have a smooth underbelly or not. The lower the better.

You want air moving over the top of the car. Obviously you will have to find a way to get some air into the radiator as well.

Bring the air dam out to the edge of the bumper if possible. Not spaced back where the factory air dam is.

No, these mechanisms reduce drag.

This would create too much drag and cause significant flow separation. It would certainly aid in adding front downforce. But would be horribly inefficient.

Not sure what you mean by gills. But again, a smooth underbody is beneficial.


Regarding the car and splitter: The lower the better. You absolutely do not want it touching the track. I don't agree with Richards statement. Once the splitter touches the ground physically. You loose the advantage of "ground effect".

Bad Karma

By gills pretty sure he's talking about the vents on the side of the car behind the front wheels. So, be better off with vents in the hood to relieve heat and under hood lift.

jbondfl

the point of a splitter is to make air go OVER the car instead of under it, soooo the lower the better, until it constantly rubs the ground.
yes, you do need some clearance in order to not tear it off on a rumble strip.
i think the "gills" you are talking about are canards. they catch that last bit of air going around the nose and convert it to downforce. I cant' comment on just how effective they are,,,,, but,,,,, the new Z06 has a version of them in its Z07 package sooooooo.
GL

briannutter1

There is a caveat to going as low as you can go with a splitter and making it act as an air dam. Air dams and vertical side skirts can be tricky depending on what the wake is doing in the back of the car. Splitters (and horizontal side skirts) are less tricky and a safer bet if you don't have access to a windtunnel to verify results.

With an airdam and vertical skirts, the wake can reverse and pack air under rear bumper and actually increase pressure under the car if sideskirts are in place. We moved the spoiler rearwards (similar to a Prostock wing) to extend the wake further and it was just enough to make the sideskirts a benefit rather than a hindrance (no longer trapping pressure under the car). Weird but true. This was a sedan in the A2 windtunnel and a Vette would behave differently (especially coupe vs. frc).

Your safest best (without the benefit of tunnel testing) would be to put the splitter at equal height to the floor. This way you have high airspeed underneath the car and the splitter is splitting air and keeping it from spilling under the car. The farther you extend the splitter...the more effective.

BrianCunningham

National SSM car

briannutter1

Always loved that car since I had my black '94.

flangley

You might be able to buy the car
call Duke Langley at 541-922-1448,

rithsleeper

Unfortunately my car still looks really good or I would cut my hood to release air. Yes my gills are the vents behind the front wheels on my c4. I really hate every splitter's look I've ever seen on a c4. They look so cool on a c5. One of the reasons is extending the fro t of the bumper straight to the ground.

The whole "touching the ground but not getting ripped off" sounds logical enough. However, I wonder why every diy splitter thread has it several inches off the ground? Is this just because they aren't really serious about performance?

In the end performance is more important to me but looks are fun too. That asm car looks like it has the stock air dam, not a splitter.

By sealing off I mean covering the bottom of the car with the trans tunnel and everything to keep air moving quickly to the rear.

Thanks for all the info, this is a good start for me to keep brainstorming.

RadnessWarrior

There is a sweet spot. Here are 2 photos I took from Competition Car Aerodynamics on Page 143. I would highly suggest buying this book on Amazon to have a better understanding of it.

rithsleeper

That does look like a good read however I'm finding it ridiculously expensive on amazon.... Just a low price of over $2000!!! And one says not printed yet to preorder..... Anywhere else to get it cheaper?

ratt_finkel

That's the same book I read recently. Excellent book. I've seen it for $40 on amazon.

steve J06

Agree! As someone with little previous knowledge of fluid dynamics, the book was enlightening and got me thinking in the right direction.

Painrace

The lower you get it the better without breaking it off. You reduce the air going under the car creating lift so you have more front down force. You may have to adjust from track to track.

Jim

yakisoba

made my own. The key points for me were:
Strong enough to handle 200 pounds of downforce.
Suspension travel that was predictable and short enough to allow lower stance needed by splitter
Flat under the car to the center of the front wheels AND higher at that point than at the nose (to create low pressure at the back of the 'undertray').
Cheap enough to replace often; it takes lots of abuse. Most of the damage I've done to the car nose lately has been loading and unloading. On track it works great.
Channel air to the wheel wells, and vent the top of the fenders. If you can't just make the undertray flat.

rfn026

Speaking of fender vents.



I'm not sure what this does for my aero but it did lower my brake temps.

Richard Newton

BrianCunningham

Yes they need to be strong enough the stand on, that's how much downforce they make

BTW Here's a Speed GT car

rithsleeper

Looks good. I am pretty opposed to cutting my hood considering how good the car looks. I might be able to channel the air to the gills behind the wheels. Like cut out some of the well and it would just spit the air out the gills. Even have a pair of garbage junk panels I could swap out that would have bigger openings.

I hate the looks of splitters on c4s so I guess I would make it detachable. Covers on the bottom would be ok on the track but I bet they would make the cab super hot in summer sitting at red lights.

With the front bumper design of the c4 I don't know how it could hold 200lbs or what material wouldn't flex and bust. Doubt abs could withstand me standing on the front, or would it be 200lbs spread out to all the mounting points? So more like 50# if 4 mount points.

6SPEEDZ

A few words on aero and ride height. While it is true downforce goes up as the car ride height goes down there is a lot more to aero. There is pitch sensitivity that you have to worry about the closer you get to the ground. This is not as important on auto cross cars as it is on track cars. When you go into a turn, creast a hill or use a curb you can lose a lot of the downforce you had right when you really wanted it. Corners like the keyhole at Mid Ohio you can have a lot of downforce on entry but right at mid corner where the track starts dropping away particularly if you have a long spliter you are now presenting basically a sail into the air. Then there is the problem of the extra load placed on the car. In another recent thread it was stated that one of our forum members was reaching 2.4 g's. While this sounds good you have to really start worrying about parts breakage. Wheel bearings, steering racks and even wheels. I know Ben had cracked one of his wheels on that car. An SKF bearing for a C5 or C6 works for sustained 1.2 g loads. 2.4 is doubling that. Not what it was ever intended to do. Food for thought