high speed front lift

[remy]

Hi there,

I' would like to achieve 170mph in my gtd.
I will set up the gear in this way soon.
Curently I coul just achieve 143mph(theorically caus my speed counter isn't that good).
Has anybody experience front lift in a GT 40? Without speed apendices, at how many it could appear?
My body is standard(mine an car's one!) and I'would prefer to avoid trouble at these speed.
Thanks for your answers.
Rémy
PS for Paul B.: don't worry for the ratinfg of the tyres ;they're good for 300kmh.

 

[Cliff Beer]

Remy, you should study some of the aero principles reflected in the 200mph+ LeMans cars of the day - look at the front splitters and vanes and rear spoilers for example. Also, look at the attitude of the car and research the spring rates, and ride heights, etc. A standard GTD at standard road height with standard springs and no thought towards aero improvements will get spooky at 170 - you might only have 100lbs on the front wheels for example. There's a big difference between say 120 and 170 and all kinds of crazy things start happening at 170+ including outside mirrors coming loose, windshield wiper arms flying around, door windows getting sucked out, etc. Ask me how I know.

 

[Jack Houpe]

My car is spooky at 135, which a not acceptable as I have had cars that will cruise at 150 mph and feel stable as a rock. The GT40 should feel the same way, my friend who has followed these cars from the original days has told me I need a slight rake on the front which would help. Just a few weeks ago I was at Silver State Classic road race, someone had the new GT there and I took some pictures of the front and rear to get an idea of what could be done. This car was in the flying mile with a speed of 176 and the owner said it felt good. I would like to make a chin spoiler that would be detachable for normal driving and diffusers for the back.

 

[J. Salmon]

Jack,

I agree, spooky in an SPF at that speed should be unacceptable. Personally, it makes me think it has more to do with alignment and suspension than aero. Your car is as close to the original racers as just about any out there, and they ran all day at 200.

Dean is running those speeds, speed220mph has done what his name suggests at Bonneville (mind boggling actually) so it is not like this should be a big problem.

If the car is getting spooky at 130, I really think it is alignment, so you should start there.

To make downforce, things get more tricky, and it helps to have the entire package coordinated. For instance, the diffuser requires the proper under-car flow management - you cannot just slap one on. I have heard that a bit of rake with the front slightly lower does help. But I cannot get past the idea that your problem is suspension setup, not aero.

Best -J.

 

[Ian Anderson]

Remy

firstly I would think you would need a full depth nostril - or pressure under youe front clip would / could cause the nostril to blow off.

Then make the car as slippery as possible - remove wing mirrors and mount wiper to be straight up.

Then start setting the suspension - about 1/2 inch lower in the front than the rear, get the correct suspension geometry front and rear

Then is should be possible

Ian
ps the Dax is very front light and wanders a bit above 120mph but I don't even have a deep nostril!

 

[Dutton]

Remy,

Have a look HERE also.

T.

 

[Jack Houpe]

J I agree, I have it set to the specs that SPF recommends but not sure if they are correct. I think Olthoff should have a go at it and see if he can help it out.

 

[Fran Hall RCR]

Jack,
What size/type of tyres are you running on the car?

 

[Bill Hara]

Remy

Try looking at the attachment to this post, it has some basic theory which may come in handy.

 

[Jack Houpe]

Fran, I have 295 50/R15 Yokohama's in the rear and 225 60/R15 Yoko's in the front. Do you think the front profile to be to tall? What do you recommend?

Bill that is a great bit of information, thanks for sharing that.

 

[Howard Jones]

If you look under your car you will see a large flat bottom. The single most important thing is to make sure that with the car on FLAT ground the front edge of the flat bottom (right behind the place where the nose section under the radiator widens out to the full width of the bottom) is 1/2 inch lower than the rear edge of the flat bottom (leading edge of the open area under the engine).

Second most important thing is to make sure ALL the air going into the car at the front exits out the top nostrils. This includes the oval holes next to the radiator inlet duct. I tape these closed when on track.

Everything else will be aero additions to increase downforce or seal the bottom of the car from air getting under it, such as a flat spolier at rear, canards at the nose or flat side fuel tank covers and splitters at the front.

Please be careful at those speeds. We don't want to hear about any "big ones" in the family.

Note: The "stock" body latches are complete garbage and WILL NOT keep the rear body work on the car at anything like the speeds you want to achieve. Put some big strong "hood pins" on it and make sure they are strongly mounted. This includes the nostril. I mounted hood pins on the floor of the radiator opening and pinned through tabs attached to the nostril. It can't come off with the pins in.

If this stuff comes off the car at 170MPH .....you're done my friend.....really.

 

[Martin]

I'm finding this topic very interesting.
Does anyone have any experience or guidance to anyone who has or is thinking about a 'dropped floor'. I never thought of it before, but the fact that the floor is about 1" lower in the middle of the car means the bottom of my car is not completely flat and this will no doubt have an effect on airflow at high speeds.
Martin

 

[Howard Jones]

Martin, there are a few GTD's out there with dropped floors, maybe some of those guys might chime in.

My basic premise is these cars are all one of a kind sort of racecars. Not streetcars but not racecars either. Every one of them are different in important ways. Things such as tire diameter, type and even air pressure will make enough difference to render direct comparisons useless.

The best way to proceed is to do your own development project. Start with the car you have and optimise it by using all of the adjustments available. Work on toe, caster, camber, tire pressures, ride height, shock setting, and spring rates. Once you have your car working as good as it will get then start improving one thing at a time until you have reached the point that that modification has yielded all it can in performance gains. Then move onto the next limiting issue.

There really isn't many short cuts in this process although much money can be saved by doing the work and testing yourself. I will add that that this is really the most rewarding part of the hobby to me.

Working at first on the street then at limited speeds on track and finally progressively lowing lap times will get you the farthest the fastest. Once you have gotten your car up to the lap times that put you into the more advanced run groups then you might think about top speed runs. I'm talking about above 150mph or so. You will not find speeds faster than this at most tracks and if you do reach these high speeds it will be for only a few seconds at the end of a long straight. If its sustained high top speeds like seen at speed trials that you are going for then I recommend you spend some time at those types of events before you go out on your own and just floor it on the freeway.

In any case I suspect any difference the 1 inch dropped floor would make won't be felt below 150MPH anyway. Here again, the main thing is to make sure that the flat surfaces on the bottom of the car are "raked". Front lower than back overall in all cases by at least a 1/2". The dropped section will be the largest airfoil on the car top or bottom and it will influence handing as much as anything short of a splitter and rear spoiler or wing at very high speeds. I am assuming that you intend to drop the floor in such a way as to make the new floor equally lowered from front to rear and thus flat bottomed as before.

If you really intend to run the car at very high speeds then consider continuing the lowered plane of the floor all the way to the front of the car behind the nose under the radiator. This will eliminate any "step" in the bottom of the car that would induce lift.

 

[Martin]

Howard,
I opted for a dropped floor in my MDA when I purchased it so it came with it already done.I was thinking head room and didn't think aero impact at all. It is indeed flat from front to back. I thought about continuing the lowest point all the way to the front. That's a good idea and one I'll consider. But as you say, get the car on the road first and develop from there. It was just a discussion point really, and one that may be more relevant to someone at a more advanced stage with a dropped floor than I am right now.
Martin

 

[Iain]

Martin,

I have a dropped floor in RF 117 to accomodate my height , the helmet and the rules regarding clearance between helmet & roll cage. I was concerned that the drop in the floor was going to be in direct contradiction with the basic theory of how to manage the air flow under the car.

I was lucky enough to get some advice from a chap called J.P. Ballard who used to be with the F1 Toyota team and has now moved to BMW to build the '09 car.

He saw my car a month ago and was not particularily concerned by the dropped floor. He gave us lots of advice on how to manage the air flow onder the car to best effect. Some of his advice is acheivable with our rule book some, whilst desirable, is not acheivable. I will post pictures as we proceed.

Martin, a slight diversion, did you know Ben & Chris Mennem in the UK circa 1970-1980 or are you another Martin Potts ?

Iain

 

[Martin]

Hi Iain,
I must be a different one. I'm only 42 (only, that would make my kids laugh) so in 1970 i'd only be four. The name doesn't ring any bells either. Back to the subject, I'd like to see the pictures. Your car is absolutely stunning.
Martin

 

[EGLITOM]

HI
I´m thinking on putting 4 linear potentiometers ( one on each corner) connected directly to the suspension movement. They will be connected to a Laptop and with a simple programm allow me to save the datas. With this and some maths one should be able to see if the car has lift or downforce and how much, assuming the static position is zero of both.

Equipment should be around 600 Euro in total.

What you think ?
TOM

 

[Jack Houpe]

My car is fixed! I took it to Little Rock to a place which use to work on the original race cars. Using some crude old machinery and math he set the car up to what the SPF specs recommended with a few measurements of his own. I think the slight rake did a great deal of the improvement. On the way home I took the car to 127 MPH (according to the GPS) and it felt like it was doing 70, the only thing I now is I wish I had a higher gear ratio at the transaxle, I was turning 5k. Open road racing will be a true test for the engine! Here are some pictures of Mike Trusty and myself at the shop, Mike Drew flew in for an air show and was with us taking a bunch of pictures, it was a great weekend.

 

[Chris Duncan]

Hi there,

I' would like to achieve 170mph in my gtd.

Synopsis

Rake, 1/2" lower in front

Aero, all air going into front and rear clips should be coming out at same pressure. The main thing here is a sealed area going into and coming out of the radiator, no leakage into front clip. This means the rad fans have to be on the front of the rad. The full depth single nostril spare cover is the most aero.

Aero, front splitter (or canards) and adjustable rear spoiler plate.

Gear ratio

Hub-centric wheels, as opposed to lug-centric.

Your car is as close to the original racers as just about any out there, and they ran all day at 200.

the originals had quite a bit of lift at speed and were pretty scary.