High speed lift problem

[jason lycett]

My car develops very serious lift resulting in lightweight steering at speeds over 70 mph. The front goes all light and the steering is almost non-existant. I have a Tornado Gt40 with standard suspension (350lb front springs , 500lb rear) correctly setup camber /toe-in Chassis is non-adjustable for front Castor. I am told this problem is common, as front air entering the nostrils creates lift under the nose. How can i best panel the chassis to stop this problem?

[Bill D]

Jason-

Does your car have the single or double nostril? The single nostril allows more air to exit, helping to prevent lift at high speed.

Bill D

[MK -IV J6]

Two ideas. A small 3/8in splitter at leading edge of nose,attached to tub,perpendicular to tub may spoil lift and a slightly higher rear spoiler may help. An inch higher ride height in the rear than the front may help as well. John Allen's book goes into the various things that were tried. You have to be very careful. You should consult with mfg. of your car and someone who races a car exactly the same as yours and test before you lock anything down.

[MK -IV J6]

Be very carefull untill you correct this condition. These cars can fly and have killed people including Ken Miles. Charringtons Motorsports in the UK race GT40's and may be able to help. Consult a race engineer before you try anything.

[Frank Catt]

Jason, our GTDs run up to 170mph without this problem, and I think you have something fundamentally wrong with your car. Firstly you mention springs, we never run with more than 75lbs differential between front and back springs, nostril panels do make a big input to how the car rides at speed, but I do think you need to look seriously at this because it will bite you if you don't. Frank

[Bob Putnam]

I can't comment on the spring rates, but I do agree with Catt about the rest. Unless the front end is 3 inches higher than the rear, aerodynamic effects shouldn't be very noticable at 70 mph. Our cars feel better at 100 than 50 mph. There's something wrong here. What tyres/pressures are you using?

[jason lycett]

Thanks for the responses. The car is riding about 5" high all round with tyre pressures of around 28 psi. The car does steer ok, but it is too light, i have gone up to 100 mph no problem, but it has no feel, like over sensitive power steering. The front just feels very light. i have the twin nostrils and really want to keep them. Surely there must be a solution to re-ducting incoming air? I have spoken with others who have had this problem. i am sure it is not unique.
Does anyone have any pictures of their radiator/nostril panelling that prevents the build up of air-pressure?

[Julian West]

Jason,

I found my GTD felt light & vague at the front, perhaps not as bas as you describe tho.

To try & cure it I first dropped the ride height at the front (as MK -IV J6 reccomends) & also stiffend the damping a couple of clicks & raised the front tyre pressure.

Malcolm M. pointed out the problem with bump-steer on the GTD's but I don't know if this affects Tornado's.. I'm sure it does nothing to aid high speed stability.

Re the nostrils, Apossible simple fix would be to make a baffle from sheet ally, that fits under the nosrtils & ducts air out.. (hard to describe but basically a flat sheet cut to shape) or I think F Catt makes a similar item.

Maybe a touch more camber would help.. does the steering self centre OK??

[Chris Melia]

Hi all

here are some photos of my modified twin nostril. I have streamlined the exit vents and extended it down to abut the ducting behind the radiator. In addition to the ducting I have installed an aluminium radiator custom made by Docking Engineering that only has a single wide core. This aids cooling by allowing the air to smoothly pass through the radiator without turbulence thus reducing the pressure build up in front of the radiator.
I would say that your spring rates are about right however your tire pressure is 5lbs to high.

Regards

Chris

Good topic, this is something I'm worried about myself.

Apparently this has been an ongoing problem with the originals also. Looking at P1021 in John Allens book they fitted large canard fins to the front for downforce. And this car had the large single rad outlet at the time. This was during a vintage race in the '90's.

Just by intuition I would confirm what's already been said. Lower front and/or raise rear ride height. Should be about 1" difference between the two. And also look at internal (front) aerodynamics.

Most likely the rad intake is more effecient/higher volumn than the rad outlet.

One thing I have noticed is that the spare tire cover (body piece that includes rad outlet) is not exact on some of the replicas. I have an old KVA body and the ducting of the spare cover does not go all the way to the radiator. In fact it is about 12" away from the radiator. Looking at the spare cover on a MarkV I noted that the ducting goes all the way down to within a 1/4" (flush fit) of the radiator with very smooth lines.

Without some type of added ducting the KVA spare cover will be inneffecient and might cause a lift problem.

Another thing to think about would be not enough anti squat in the rear suspension. Imagine going 70 mph and slamming the throttle. What if the car squats hard and adds to an existing front end lift problem?

[Brian Magee]

Hi Jason

Try lowering your tyre pressures. The GTD manual states 21psi for front and 23psi for rear. Era suggest 22 & 25psi. They also state tyre noise and harshness become serious above 25psi.

Brian

[jason lycett]

Thanks everybody, and thanks for the great photos chris, this looks exactly like the sort of thing i need to look at.

[M.B]

Hello, !

Just a small note..
Remember that MkI and III differs as well...
When you buy such a vehicle, you need to finish it !
Non are perfect, they have to make a living as well...
Development costs.. [img]images/icons/grin.gif[/img] [img]images/icons/grin.gif[/img] [img]images/icons/grin.gif[/img]

[norman falkiner]

Chris. That looks a really well thought out solution. It appears in your photos that you are not running a cooling fan or fans. Is this right? regards

[Chris Melia]

Hi Norman

I have two 1100 cfm cooling fans placed in front of the radiator pushing air backwards through the radiator, I thought that this would help to shield the radiator from impact damage, keep the fans out of the hot air gas stream and also keep the exit air from the radiator less turbulent for its passage over the car. I run a 351 V8 and have not had any over heating or front lift problems.

Regards

Chris

[ April 12, 2002: Message edited by: Chris Melia ]

[ April 12, 2002: Message edited by: Chris Melia ]

[MK -IV J6]

The pic on the 917 thread of my MK-IV shows the splitter under the nose. I don't know if this was used on MK-I's II's,orIII's.

[M.B]

Hello J6 MkIV

I can´t say that it never occured.
But i do not think such items were mounted on MkI´s and III´s at least.
Some MkII´s had them.
At least P1012,XGT2,P1015,P1047 and P1032 had them at some point.
But not full lenght..
Some did have fins in front of the wheels.
Different types of "Spoiler" under neath in front.
"vind visors" in the rear part of the front wheel housings following the curved line.
Even in the upper part of front wheel housing.
Different splits etc.. in side the nostril etc..V formed as well as straight ones etc..
Even a shield in front of the wiper...

Different splits in the front part of the nostrils were the "holes" begin...
Even a spoiler !
Mostly on "trial"..

Regards,


[img]images/icons/smile.gif[/img]

[MK -IV J6]

Hi MB
You are right Tenant/Abby. The MK-IV's also have "turbine" wheels which extract air through the brakes out of the wheel wells which also reduces lift. The J car that Miles was killed in had 16inch wheels which may have contributed to his crash and the move to 15inch wheels on the MK-IV. There is a picture of the turbine wheels on the 917 thread. (There is no official or even agreed upon answer as to why Miles crashed) As far as the raison d'etre for any of these cars I am taken with Enzo Ferrari's statement to the designers of the F40: "I don't care if the car has has electric windows. I don't care if the panel gaps are crooked but, when he steps of the accelerator I want him to shit his pants."

[M.B]

Hello, MkIV-J6

16" wheels...hmmm.
Did´nt thought about that one/or did´nt know..?
Interesting..
My kind of guy;
Enzo´s words words goes for me too !
He was not much of a politician...
He was a ruler...
Is your MkIV the ex Lindley or the ex Ford museum piece ?
Kind of confused...

[img]images/icons/rolleyes.gif[/img]

[MK -IV J6]

Many are re J5/J6. LeMans records said J6 was the winner and J5 came in fourth. The records were wrong. J5 Foyt/Gurney was the winner and J6 Donohue/McLaren came in fourth.
Ford was confused as well and painted J6 red,added a Gurney bubble,and sent it to autoshows as the winner. They then gave it to Foyt who sold it to Lindly who sold it to Lavanos who I bought it from. Lavanos and the Ford Museam inspected J5 and determined it was the winner as the tub had be crushed under the seat to give Gurney even more headroom. J5 is still in the museam but is missing it's chassis plate, original engine, and radiator. It has a "Do not start" sticker on the dash. I repainted J6 in it's proper colors and it now looks as it did at the start of the 1967 24 hours of Lemans. J6 still has it's original chassis plate.