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Discussion Starter #1
Situation:
ZX3 cruising along at speeds from 90-140 mph.

Goal:
Average 115 mph over 90 miles, With as much stability as possible.

I need some help with ideas on how to make the car stable at speed, without creating too much drag. I need help with suggestions /Ideas for the front and rear bumpers and rear wing. These will only be used for racing, not on the street, so a bit of removability is needed.

I have a spare front and rear bumper to work with, and a very limited budget.

I have a few ideas myself, but would rather keep quiet and be thought a fool, that spout off and prove it. I eagerly look forward to your guys' input, and the subsequent discussions.

EDIT: I dont know if it makes a differance, but the car is fully gutted except for the dash and front door panels. I was thinking Id ptobably need about 1-200 lbs of DF on the end of the lip, is that right?
 

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I was actually talking to Louis today about aerodynamics for the most part we never go fast enough to really make them useful.

Now that isn't to say that some cars can have extraordinarily BAD aerodynamics that can cause problems.

The focus is fortunate in that it seems to be pretty good on its own.

I'm sure someone here is a resident expert but you could probably ask Louis on Saturday (after Fridays Redline event)
 

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I didn't catch too much in the thread about "Splitters", but there May be some info there...
I also had a thread about the effects of lowering on Aerodynamics, and it seems that the front face of the front tires actually create more drag than you'd expect.
 

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I'd take out a good chunk of the back of the rear bumper cover. ALL the way across, and go up as high as it looks like it'll do some good. Otherwise it'll act more or less just like a small parachute back there. If you don't want to cut the back out totally then consider swiss-cheesing at least the bottom few inches with a hole saw. I know CTZX3 did this on at least one of his bumpers... Do what he did, only more.


Front and rear under-tray/diffuser type stuff might help too if done properly.

Did I read right a while ago that the S2 (I think it was, maybe the Street Edition too) had some sort of lower front lip? Lower than the regular bumper. That might help, or it might hurt you. Tough to say.

Also, consider the Focus Sport/North Viking '99 WRC wing. It's adjustable and might help you dial things in. Pricey, though.

Additionally, consider cleaning up the aerodynamics with some decent duct tape (or equivalent 150 MPH tape
). Seal over the sides of the hood, remove the wipers and maybe smooth that area over (unless it looks like it might rain, of course... but then do you want to be trying for 140 MPH?). Seal up around the headlights, over the foglights, maybe even over the lower and/or upper grills (though the radiator and air intake will still need some air, just how much I'm not sure).

Make sure your tires are up to it. Balanced VERY well, properly inflated, maybe a bit up from street driving to stiffen them up and reduce their tendancy to squirm as well as reducing rolling resistance.

That's all I can think of at the moment (other than the other car prep stuff, like making sure the brakes are good/flushed, making sure the suspension is all there, everything is tightened down, etc.). Good luck!
 

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The key to low drag, high speed stability is minimizing the air under the car. Sheet aluminum and pop rivet works well for a DIY air dam. That said, I have had my Focus at about 115-120mph (Roebling) at factory ride height and the car is Rock of Gibraltor stable. I am not sure how much you need to do.
 

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my teammate (hatchblack) recently put a flat solid air pan underneath the front end of his Focus. It made out of plastic...he also installed the stock SVT lower bumper shroud....He notice improves on our local track....speeds climb to about 90-95. It really helped when he went off course, decided to run over some tires. It lowered his repair bill, because everything was covered and protected!
 

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I think you will be OK without any aero stuff at all. Nearly every day I drive at 80-90mph on the freeway and the car is rock solid stable. At Shannonville I reach speeds of about 110mph on the front straight before I stand on the brakes and again no problem at all with stability. I have had the car up to over 140mph and again no problems at all very stable.

Now as far as drag is concerned the first obvious simple step is to remove the antenna. Then maybe fab up a front splitter of some sort. Thats about as far as I would take it unless you really want to get crazy.
 

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I suggest that you contact some of the other racers that have been doing these events. They're a wealth of knowledge and are willing to share information.
 

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Discussion Starter #9
The antenna is already gone (after a carwash banging it around, I said screw that and took it off).

I have started on a rear bumper with a hole saw, but i like Charles' idea better. Just cut it!

As for the front air dam, would it be possible to use the garden lining stuff (like 5 inches wide, stiff plastic with a rolled lip on the edge) instead of sheetmetal? Or should i just save up and do it right, with metal.

Man oh man, i've been looking at the north viking WRC wing since I got my car, maybe i can find one used or something. But failing that, what about just a good old fashioned SVT wing? maybe even an SVT wing with a sheetmetal/plexi extension off the back?

Thank you for your help so far.
 

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I'm no aerodynamic guru but after reading Fred Puhn's How to Make Your Car Handle it sounds like the key is going to be to reduce the air flow under the car (as teamDFL pointed out) and to address any areas where there is air seperation.

Seems like there are three types of air flows: smooth, turbulent and separated. Smooth is just that, flows along the body smoothly. Turbulent is where the air is disturbed and might flap around, but in general continues along the body of the car and doesn't cause an awful lot of drag. And separated, which is the worst as it causes low pressure areas (i.e. often causes lift) as well as massive drag.

The book talks about "tuft testing", which is taping small pieces of yarn to the body of the car and watching what they do at speed. They talk about figuring out max downforce before stalling using a rear wing, by attaching yarn all around the wing surfaces and looking for this separation effect.

Greg- Jay and I have been talking about doing this for a while now. He's got a blue car which should make a yellow or white yarn show up pretty well. Maybe this weekend?

And regarding air flow under the car, sounds like a simple reinforced front air dam would be easy enough to make and maybe even some short side skirts.
 

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Here's a list of simple items that'll help:

Duct tape all body seams on the front of the car.
Pull in mirrors.
Prop up the rear of the front hood about 1 - 1 1/2 inches.
Have a plexiglass shield made for the grill. Drill small holes for air flow, but you'll have to experiment how much and where.

Here's an example of a friend's 5000 lb brick showing some of the above items. It techs to 185 mph and is still a daily driver:



BTW, at speeds above 150, the front end lifts about 2".
 

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A Friend of mine who road-races an IT-prepped Civic has a thin metal Air-dam that is almost vertical, which wraps the front of the car, almost touching the ground. The bottom couple inches is plastic or rubber like the garden-plastic you described, so it doesn't crumple if he hits the rumble-strips, and it's easily replaced when worn.
It is contoured to the curvature of the overhead view of the front of the car, but it's basically pop-riveted into place, and it's purpose is to prevent air from going UNDER the car.
I think that's the main area to work on, and I wish I knew more about splitters.
I'll have to go back and read that thread in full...
 

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I'd say it'd be largely to help deflect air over the windshield more smoothly.
 

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Prop up the rear of the front hood about 1 - 1 1/2 inches.
Is this for downforce, or cowl induction type cooling, or both?
Neither. At speed, there is a pressure build up underneath the hood and it allows the air to escape.

Regarding aerodynamics, this car has won the 165 mph speed class:
 

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Makes sense, except for the hood propping thing. This has come up on many forums and If you look at what is happening (yarn tuffs) the areas in front of the grill and windshield are high pressure areas. Air can't exhaust through the grill or cowl area in front of the windshield. (good reason our ventilation systems that vent air INTO the car are located there). Vents in the front 2/3 thirds of the hood may exhaust underhood air into low pressure areas over the hood (think Bernoulli), which may also disrupt lift on the hood. The whole idea of cowl induction was you had a high pressure source in front of the windshield with "Free air", as a front facing scoop acts as another source of drag. make sense? The "airdam" close to the ground prevents air building under the car (air=lift) at the same time it causes a low pressure area (sunction). This not only pulls more air through the radiator (high pressure to low pressure), but pulls the car down- opposing lift across the hood area. Open the back edge of the hood and you allow another area for high pressure air (building in front of windshield) to enter, negating some of the benefit of the airdam, reducing cooling air flow through radiator and sunction under car. N'est pas?
 

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If you want my input I have about 12,000 miles logged at or above 100mph sustained with the cruise control on. Stock body and 4" lowered ft and 3" lowered rear. Above 110 mph the car is forced to the road becouse of the natural rake of the body. A small OEM Ford hatch spoiler will propaply help out in the rear. The ST 170 24 hour race Focus's do not use spoilers and run up towards 160-170 mph on the front straight of the Nurburgring. But they are also just as low as my car if not a little more.
 

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jinstall you are THE MAN in more ways than one!
 

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I agree spoiler may hurt top speed because of drag, as rake has to do with top speed obtainable, the sucky part comes from controling air UNDER the car. Air over the car at 150 mph does not hold you down- it tries to lift you off the ground- think 60's sports cars-, it is the suction of the low pressure created under the car by blocking air going under the front that holds you to the road. Think about a venturi under the car where an enclosed area goes from a small area opening to a large area-NACA duct shape. Either air will rush back in to fill the void, or the car will lower to fill it, hence downforce-actually suction. Airflow under the car is all about making a void (vaccuumm) and then filling it with chassis, instead of air. Think sucking a golf ball through a garden hose........sigh. The golf ball doesn't move because the AIR on the other side is pushing it, it moves because it it trying to fill in the void caused by Suz..I mean vaccuumm.
Make sense?
 

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Discussion Starter #20
Actually, It does make sense


So the general concensus seems to be an SVT wing, deep front air dam and saping up all the gaps and I should be ok?
 
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