VitaminJ New Reader
6/21/08 9:29 p.m.

This is my project car. It's a 1986 Honda Civic hatch 1300 with an Si motor swapped in. It's got high compression pistons, cam regrind, porting, valve job, and balancing among other things. It's got adjustable Tokico Illuminas, big front brakes off an Acura Integra and rear aluminum drums. I build it to be a GT Lite car for the street, I've always loved those cars. I am unsatisfied with the aerodynamics of this car and would like to make them better. I have done a few things, basically copying what I've seen at the track.

I built an air dam with wheel dams:

I started on the front undertray, unfortunately I ran out of Coroplast for the corners

I added a Gurney flap to the rear hatch

I then covered the fuel pump. Before:


Am I on the right track? I plan on building some sort of rear diffuser. I also want to build side skirts, but I have no ideas on how to approach it without making it look like crap, any ideas?

Anyway, the car is easier to drive on the highway after the mods, requiring less throttle to keep speed. It also feels much faster over 90mph. I plan on tuft testing the Gurney flap against the stock wing and nothing.

I did some tuft testing today:

Now tell me what I'm seeing. On the fender shot it looks like there is very little turbulence right behind the wheel, but after the door gap, it starts getting turbulent. The flow is smooth over the top like I'd expect. It looks like from that shot at least that my wheel dams aren't hurting, usually there is lots of turbulence right behind the wheels.

Next we see the roof of my car. It appears to me like the Gurney flap is doing exactly what its supposed to. From what I've read they are designed to stop airflow directly behind it, this causes vortices directly behind it which help the air flowing over the top do break away from the body/wing smoother. I didn't get footage, but I also had tufts on the rear hatch glass. There was very little movement from them even at 70mph, is this bad? They were moving mostly side to side, and were not getting blown up the top.

What other key areas should I tuft test? I plan on adding wheel dams in front of the rear wheels and testing before and after this time.

Thinkkker SuperDork
6/23/08 3:32 p.m.

Was that vid taken from in front of the gurney? For some reason it seems that air was not fully getting to the flap. Though as speed increased the movement was more noted. Without a gauge of speed I cannot say on it.

You have a drop at your hatch witch can make it hard for air to get to the flap. Add some canards at the top of the roof and it will make the gurney much more functonal.

Also your vid behind the wheel I do not think you will start to see a lot of difference there.

What is your goal? MPG? Downforce? Or just a exercise in practice?

VitaminJ New Reader
6/23/08 7:18 p.m.

Well, this is my track car. It starts to top out around 118mph, but I know it could go faster. I want to improve the aerodynamics, not so much for downforce, but less drag. I shortened the air dam today so it only extends as low as the lowest point on the car.

Yes, the Gurney flap does not get a lot of air. Though I was doing some high speed manuevers the other day to try and get the rear loose, and I noticed it felt much more planted that without the Gurney flap.

I also want to do testing with the stock spoiler and no spoiler. Where should I do tuft testing specifically? I plan on doing coast down tests with and without my mods to see what impact it actually has, though it does feel much faster over 70mph.

Thinkkker SuperDork
6/23/08 7:42 p.m.

Make a cover over the rear wheels. Finish the undertray and do it acros the entire bottom of the car. Keep the windows up though you cannot on track.

Vent your wheel wells, it can lower the pressure buildup at speed and allow the car to move more easily.

VitaminJ New Reader
6/23/08 9:02 p.m.

I won't skirt the rear wheels, but I will make dams.

I will solve my windows down problem by venting the rear of the hatch, somehow.

I'm going to box off the rear inner fender to the bumper cover instead of venting behind the wheels.

minimac Dork
6/24/08 7:52 a.m.

You might want to experiment with closing your grill opening as much as possible to limit the amount air getting into the engine compartment. Close off as much as you can without effecting cooling, and possibly add some louvers to help vent the underhood area. What you've done so far looks good and should work well. Take some clues from the nascar racers. Say what you will, those fellas know how to get a box through the air. Instead of just adding height to your rear flap, slot the bolt holes so it can be adjustable. The same with your airdam. That way, you can adjust for street or track time without undoing what you've done. A little more coroplast underneath and you should see and feel a huge improvement. BTW, nice job on the airdam!

pinchvalve SuperDork
6/24/08 9:53 a.m.

I assume that you remove the wipers before a race. They can cause some drag.

boofighter HalfDork
6/24/08 10:10 a.m.

iceracer New Reader
6/24/08 10:32 a.m.

With the air dam and running on track be sure to install some brake ducts.

VitaminJ New Reader
6/24/08 1:30 p.m.

I am leaving all the grill openings until I get a new radiator, I need the cooling this summer. It's usually around 100 to 110*F at the track

Making the flap asdjustable is a great idea.

Also, brake ducts are already on the list!

Thinkkker SuperDork
6/24/08 2:02 p.m.

If you did do side skirts you could "lower" the car, at the least the bottom edge. just attach across between them. Make like a false floor. Only question is the stress it would need to take as in the air pressure.

VitaminJ New Reader
7/3/08 12:25 a.m.

Today I did the brake ducts. The front coroplast undertray was not up to the job, I plan on replacing it with aluminum now. After a quick test the brake ducts are cooling the brakes, how much I'm not sure. I plan on mounting my camera underneath and see if I can make some sort of visual and see how much air is flowing. I basically copied what I've seen on other cars at the track though.

I plan on screening off the inlets.

This is a pretty tight kink, though it was needed to avoid rubbing the tire. I think it will be ok though.

There isn't a lot of room to get the duct in there.

At full lock:

I also raised the hood a hair more:

stumpmj HalfDork
7/3/08 7:39 a.m.

Try some underhood ducting for the radiator/oil cooler. That will help clean up air flow through the engine bay.

Why raise the back of the hood?

John Brown
John Brown GRM+ Memberand SuperDork
7/3/08 7:54 a.m.
stumpmj wrote: Try some underhood ducting for the radiator/oil cooler. That will help clean up air flow through the engine bay. Why raise the back of the hood?

To lubricate the wipers with the oil leaking from the valve cover... duh! ;)

iceracer New Reader
7/3/08 9:20 a.m.

With the rear of the hood in a high pressure area , I don't see the benefit of raising it.

VitaminJ New Reader
7/3/08 9:32 a.m.

The idea behind raising it is to vent air out over the windshield instead of out underneath. Like the pull through rad ducts on NSXs and what not. That was my idea at least. From what I've heard recently it actually lets more air into the engine bay.

I already made ducts to the radiator:



stumpmj HalfDork
7/3/08 9:10 p.m.

I actually meant ducting the air after it leaves the radiator. Letting it flow through all of the crap under the hood causes drag. I'd recommend venting through the wheel wells. You'll need to vent the high pressure air that gets trapped in that area anyway (as was pointed out earlier) which makes it a logical place to send the radiator air too. The high pressure air entering the front of the rad will be more than enough to push out through the wheels wells.

VitaminJ New Reader
7/3/08 10:00 p.m.

Oh I see, so you mean making the same kind of ducting behind the rad to make it flow out the passenger side wheel well?

stumpmj HalfDork
7/4/08 6:21 p.m.
VitaminJ wrote: Oh I see, so you mean making the same kind of ducting behind the rad to make it flow out the passenger side wheel well?

Exactely. Air flowing over everything under the hood causes drag just like everything over the hood does. Ducting the air out will eliminate that drag.

Apexcarver New Reader
7/4/08 7:28 p.m.

actually, there is a high pressure area at the base of the windshield, hence why cowl induction is popular with mustangs and camaros....

(air will wanna go in, not out there)

the best solution is if you were to do something like they did for the hood of the shelby series 1.

the question is if you have the space to route something like that.

or try something more like this hood setup

you have to make an inner shroud for the engine that goes in front of the engine and behind the rad allowing enough space for air to leave the rad.

neon4891 HalfDork
7/5/08 1:34 a.m.

+1 on what apex said

VitaminJ New Reader
7/5/08 10:59 a.m.

I'm going to drop the hood back down to stock. I have a buddy who can make louvers, so I'll punch some in the hood when I get a chance to get down to Albuquerque.

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