Aerodynamics for high speeds

[N/Angel]

I have been racing our 2015 Ecoboost at Rolling50 1000 events this season. The race starts from a roll at 50km/h and the car with the highest top speed after 1000m wins. Cars are grouped by horsepower.

Now I'm aware this is the open track forum, but you guys are probably the best to ask aerodynamics questions so here it goes:
The Ecboost was fun but it is not very good at this kind of racing. Prepping my 03 GT for next season, taking it apart one more time this winter, adding a coyote engine and auto trans out of a 2015 GT.

Other then the engine, what makes these cars go really fast and achieve a high topspeed??

any input and suggestions appreciated, I'm on a budget but I'll consider everything. The speed I'm dreaming of reaching is 250km/h, that was the top speed in the 400-500hp class at the last event (490hp Porsche 996 Turbo).

thanks :beer:
Ana

 

[noldevin]

A tiger racing hood will help allow air under the hood to escape without creating lift, which should reduce drag. Some skip the hood and cover up a big chunk of the grille(s), but that can hurt your cooling so you have to be careful. Some tape over all the seams in the bodywork, not sure how much that actually does

 

[N/Angel]

I have a TrueForged/Racebronco hood on the way, so hope that does make a difference.

any idea on rear wings? I was looking at the stock Terminator spoiler to reduce drag, what do you all think?

 

[racebronco2]

A tiger racing hood will help allow air under the hood to escape without creating lift, which should reduce drag. Some skip the hood and cover up a big chunk of the grille(s), but that can hurt your cooling so you have to be careful. Some tape over all the seams in the bodywork, not sure how much that actually does

The hood is a must. Do you think it is a better idea to push a wall of air out of the way or get the air sucked thru the grille opening out the hood vents and actually create downfrce?

 

[noldevin]

The hood is a must. Do you think it is a better idea to push a wall of air out of the way or get the air sucked thru the grille opening out the hood vents and actually create downfrce?

It's not necessarily better to have it go through the grille. Then it has to push through the radiator and past anything else between the grille and hood vents. If you block off most of the front it gets split off to the sides and over the top mostly. A gt500 hood wouldn't be a bad choice as it was designed to get the gt500 to 200mph

 

[racebronco2]

I have a TrueForged/Racebronco hood on the way, so hope that does make a difference.

any idea on rear wings? I was looking at the stock Terminator spoiler to reduce drag, what do you all think?

At one Mojave Mile event 3 terminators showed up, Terminator 1 whippled powered 550rwhp, Terminator 2 ported eaton at 480rwhp with my 1st hood design with just the recessed opening lowered 2 inches, Terminator 3 my 520rwhp ported eaton with similar to the newest group buy. All cars weighed about the same, same gearing and all of us had some type of weigh reduction, i was probably the lightest of the three. Terminator 1 did 162mph, Terminator 2 hit 163mph and my car did 172.3mph.

 

[racebronco2]

I posted in the road kill drive thru that i was going to the Mojave mile and what chance did i have against the C6Zo6's. Most people said no chance, others said the C6ZO6's are top end monsters and i am taking some good drugs to think i even had a chance. Posted my results that i was about 6mph faster than most of the C6ZO6's, 3 mph slower that the ZR1 and 5mph slower than a modded ZR1. I got bashed for making up lies and i didn't have proof, my 172.3 wasn't posted because i went over my safe speed with the safety equipment i had. A well known tuner actually took a picture of the clocks with my car as it crossed the line. All the bashers went silent after they say the picture. The few that didn't think i would be faster congratulated me.

 

[racebronco2]

It's not necessarily better to have it go through the grille. Then it has to push through the radiator and past anything else between the grille and hood vents. If you block off most of the front it gets split off to the sides and over the top mostly. A gt500 hood wouldn't be a bad choice as it was designed to get the gt500 to 200mph

I guess you don't know much about the history of my hood design. I have known Paul Brown years before he passed away, more of an acquaintance, he was checking out my hood, we talked a little and i said i wanted to make the recessed area further back, his reply was "In my wind tunnel testing you will have too much turbulence, It would be better if you opened up the recessed further back and add vents. In our testing the louvered hood will suck the air thru the radiator opening and because the vacuum is so much it will suck the car to the ground giving you move down force". So as you can see the air is being sucked thru the radiator opening.

 

[racebronco2]

Any spoiler or wing will slow the car down. High speeds runs you can get down force on the rear by lowering the front as much as possibly and raising up the rear.

At the Mojave Mile at around 150 to 160mph me and my friend actually took our hands of the steeringwheel to see if the car was stable, we talked over dinner and we did not know the other person had took their hands off the steering wheel. Both cars went straight, my friend even said that that one of previous cars was a twin turbo Porsche and his car was more stable at 160mph that his TT Porsche at 130mph, he said over 130mph you will never dare take your hands off the wheel.

 

[iismet]

As already stated, a wing will add drag. If you need balance, you could try a terminator rear spoiler. If it worked, I would remove it and start messing with gurneys attached to the rear lid trying to find the smallest that would provide stability. Vortex generators at back of roof may be of benefit to shape air moving to gurney.

The bottom of an SN 95 is really dirty. Dirty air causes drag and lift. Lower the car, build a front air dam, add a splitter, sheet the bottom, build a bottom diffuser, add sill splitters. Make sure there is a little slope from back to front with nose lower. Search for pictures of bottoms of modern production sport cars , Ferrari, Audi, Aston, Porsche, C7.

Try to get control of the air top and bottom with emphasis on reducing drag. Limit intake air to only what is needed to cool. Block any ports not being used.

The 3rd revision of Simon McBeaths book is really good.

https://www.amazon.com/Competition-Car-Aerodynamics-New-3rd/dp/1845847768

chr

 

[N/Angel]

At one Mojave Mile event 3 terminators showed up, Terminator 1 whippled powered 550rwhp, Terminator 2 ported eaton at 480rwhp with my 1st hood design with just the recessed opening lowered 2 inches, Terminator 3 my 520rwhp ported eaton with similar to the newest group buy. All cars weighed about the same, same gearing and all of us had some type of weigh reduction, i was probably the lightest of the three. Terminator 1 did 162mph, Terminator 2 hit 163mph and my car did 172.3mph.

thanks for posting speeds, based on what you did with your horsepower I sure would need to add a supercharger to my Coyote swap to be somewhat competitive as it seems.

 

[N/Angel]

I'd appreciate more info on the front splitter, I thought that on the Cobra R, the front splitter with the wing actually reduced top speed, so wouldn't adding a splitter be counterproductive?
Excuse me if this is a dumb question/assumption.
Looking at the other cars at the events, none of them run a splitter, just stock bumpers mostly.

 

[598]

Stan ran a big front splitter on the 95R silverstate car we raced, and it was very stable. He did run it as a solid piece under much of the engine compartment. We were restricted to 165 so that's all we ran, but we cruised at 163 for ever, without working the engine too much at all. That was supposed to be the last run before we teched unlimited to bust 200. A Cut tire ended the story early. That was with a pretty straight forward 408.

 

[iismet]

This one is from Maier Racing.

We had to build the dam and figure out how to attach it. We got down force as soon as we installed it. It is currently configured < 3" off the pavement. It is not a big shelf. I believe it works because we have accelerated the air under the car specifically at the axle line - we run a fully sheet-ed engine. The pressure is much lower there than stock. The rest of the air is directed above and around the front bumper cover. As you can see we have away to go on the sheeting - the work we have, made a significant difference in handling. Turn 9 at Portland is off camber and the car wanted to drive off (around 110). Our first shot with the splitter and we were driving it flat out which lead to MM3 components and bump steering the car.

Tuck exhaust up high

Splitters are not recognized as adding drag. The sill splitters extend into the sub-frame connectors. You do not want to drag air under the car. Rather force it thru a venturi with speed . You wish you could run the air faster under the bottom than over the top.

We run 1/8 inch of slope rear to front this gives us a venturi in side view (ours is weak without more sheeting). It is evolution for us. We modify it, run it, and check lap times and feel. The more you can sheet the better. We originally ran the Cobra hood with the vents punched out, but have since changed to a more free flowing hood and the cooling is boxed. This is another aspect of getting control of the air.

Meir has a shallow and a deeper one for flairs. Ours is shallow and we run trip fencing on the fenders because of the offset of the Enkeis.

At the rear the Terminator spoiler could be used as a baseline. As stated, I would try to get rid of it, but it may be that a Gurney attached to the spoiler could work well. Gurneys are not recognized for adding drag, but do help clean up the air - dirty air causes drag. Pretty sure Maiers spoiler is not what you want, but it all takes testing. A Maier spoiler could be purchased and cut down.

On a speed car I would lower the front splitter down to 2" off the ground. This will complicate your effort because you will need to remove it for transport. We are too lazy. I would space the bottom panels down. I would try to get slope with suspension setup, but would consider building additional slope into the floor if needed. I have seen studies where bottoms less than 2" lessened ground affect. You can really see the slope on current F1 cars.

I recently acquired this

It comes from the factory with a sheet-ed bottom. It is sheet-ed from the front bumper to the back of the engine.

Top speed claimed 175 - 3600 lb - 380 bhp. No splitter, no spoiler, no diffuser. Intake is boxed cold air, cooling is boxed, bottom is sheet-ed. I smiled when we put it on the rack because it increased my confidence we are headed in the right direction on the Cobra. It won't hang with a stock SVT on the street, but out of the box pretty sure it would get one on the track. (It will not hang with my Cobra on the track - it's not quick enough) The engineering, execution, and balance are beautiful and it is much easier to drive at the limit (49/51 with lower cg).

Our stuff is crude - it has been an experience in learning how to keep it attached.

If you have to turn at speed all bets are off :-D - I would think wing and enough HP to drag it. The air under this car is ripping - not fast enough Notice how close he is drafting. Is it possible he lost flow to the bottom?

[video=youtube;8snP33Ga3X4]https://www.youtube.com/watch?v=8snP33Ga3X4[/video]

chr

 

[racebronco2]

The issue with running a splitter is that you are covering the underside of the bumper opening. The high speed runs i leave the bottom of the bumper cover open because i have found that there is no way at 150mph plus that enough air will go thru the grill area. One member years ago went to a high speed event with the radiator boxed up and he said the car felt unstable and would wonder a little. I do not know what speed it would effect the car. I do run a mach 1 chin spoiler.

 

[iismet]

The issue with running a splitter is that you are covering the underside of the bumper opening. The high speed runs i leave the bottom of the bumper cover open because i have found that there is no way at 150mph plus that enough air will go thru the grill area. One member years ago went to a high speed event with the radiator boxed up and he said the car felt unstable and would wonder a little. I do not know what speed it would effect the car. I do run a mach 1 chin spoiler.

Were you running the AC condenser?

 

[racebronco2]

At the time i was.

 

[GordsFord]

Race Bronco do you mean not enough airflow through the grille area for cooling or do you meant not enough airflow through such that it is affecting the aerodynamics for lift and less speed?

Thanks,
Gord

 

[racebronco2]

Race Bronco do you mean not enough airflow through the grille area for cooling or do you meant not enough airflow through such that it is affecting the aerodynamics for lift and less speed?

Thanks,
Gord

Effecting the aero, to much restriction of air flow thru the grill opening. Cooling was never a problem once i used a real heat extractor hood.

 

[N/Angel]

I stumbled across this diffusor on facebook, will this do any good or would it be just for show?