GT40 Highspeed Behaviour

[EGLITOM]

Dear all

would like to start a thread with the idea of exchanging the specifics of highspeed behavoiur of our GT40s.

To start with this is the experience i had.

Speed was a GPS veryfied 181 mph ( at 7200 RPM and hitting the revlimiter). More to come when i set the revlimiter to a higher level ( up to 7800 RPM possible according to my engine builder)

The experience was quite good. Car behaved very nice, it run dead straight with almost no correction needed ( tiresize front 225 a little toe out, rear 345, a little toe in). I could have driven the car one handed.
Also bracking was no issue when i had to brake down to 150 mph, because of a slower car unterestimating my speed.
In terms of front end lift i can not tell if there is some significant amount.
The RCR40 behaved defenitely much more controllable at those 295 kmh than my previous 964 C2 ( 310 HP, with optimised PSS9 Bilstein Suspension and 18", the front tires where 245´s i think) at 270 kmh.
I also had no issue at all with lift of the top of the doors . My retainers seem to hold them down very well.

To tell more i plan to install a 4 corner way measurementsystem which a friend of my cousin is producing.
Waycon Positionsmesstechnik(english)

With this i will be able to tell if there is lift on which axle and how much.
This than in combination with the weight per axle and wheelrate of suspension should enable me to also calculate the lift in kg.

First i would like to start with a list of GT40´s owners who have done above 170 mph in there car and ask them to share there experience.


TOM

 

[William Quantrel]

Fantastic Tom.

I have no experiences to add but do have a few questions.

Your RCR sounds very SOLID - well engineered.

What tires are you running? What are the pressures?

What is the ride height from and rear?

Is your engine a 331 or 408? What are your hp/tq numbers?

My math tells me that 7800 rpm will see 196.08 mph (not taking into account real world driving conditions such as drag, fraction, wind etc...)

7900 rpm = 198.6 mph
8000 rpm = 201.1 mph

 

[Kevin L]

Tom,

There was a gentlemen named Mark Levey (sp?) on this forum that did the same thing with his ERA. If I remember correctly he was also attaching sensors to each axle to calculate lift. I cannot remember if it was an outcome of that test but I know he added a front splitter and side skirts to his 40 to assist with aero.

I am very interested to hear your results. I have not taken mine past 140 and am not sure I will have an opportunity for a while.

Kevin

 

[EGLITOM]

Dear William


check out this post for the engine details

http://www.gt40s.com/forum/gt40-build-logs/24525-toms-rcr-40-trackracer-6.html#post234880

this posts contains information about the gearing
http://www.gt40s.com/forum/gt40-build-logs/24525-toms-rcr-40-trackracer-16.html#post277822

http://www.gt40s.com/forum/gt40-build-logs/24525-toms-rcr-40-trackracer-26.html#post333795


TIres are Pirellis Pzero assimetrico. Front 225/50/15 rear 345/35/15, they are Z rated.

Ride height front is 4" rear is 4,75". The adavantage of the low profil tires is that you can achieve such low front ride height without compromising the suspension geometry. if one is using a /55 or /60 tire the diameter would be bigger and thus the ride height should be higher by half of that additional diameter .

here are some more details about the suspension setup
http://www.gt40s.com/forum/gt40-build-logs/24525-toms-rcr-40-trackracer-27.html#post337339

TOM

 

[William Quantrel]

506 hp and 431 tq. Very nice.

I have read that Gordon Levy does magic with 306 and 331 cubic inches.

I hear he makes a 8000 rpm, 500+hp 306 that doesn't stop pulling at any speed. Why did you choose 331 cubes?

I recall Gordon writing about his experience driving a GT40 that had one of his 306 motors in it with 8 stack EFI and reported it sounded like an F1 car. The induction noise was shocking.

Did you notice at 150-181 mph the steering getting light from front end lift? This has been a common complaint.

 

[roaldin]

I've commented on this in another thread.
Fastest I've done so far is around 170mph so I guess I qualify.
My experience sounds much like yours - not a problem. No noticeable lightness in the front end, no bits of body lifting etc. Braking from that speed presented no unhappy surprises from the rear end so I am very happy with the car in that respect.
Not sure on power/torque figures of the current engine as the dyne broke mid tune - proud of that - engine is 364 ci and runs 50mm 8 stack injection.

Tyres are 225 front 265 rear. Other data I'll have to dig out.


Tim

 

[Paul Thompson 'Hooligan']

Just to add my 5c, I've driven Roy Smart's MK1 GTD40 to 183.6mph (laser and GPS verified) on a standing 1.2 miles and it was still pulling hard. Revs were at about 6600 as I recall and steering did not feel at all bad. The car was not particularly set for speed, although it did have a slightly nose down attitude as the rear road tyres were of a larger diameter than the slicks normally used, meaning the lower chassis rails was about an inch higher at the rear than the nose.

The car has light-weight fibre-glass body sections front and rear which with the 'twin-deep' nose section did give some concern as I could see that the nose section was trying to lift from the body section at speeds above about 155mph.

Car was running 245 50 15 Avons on the front and 295 65 15?? Pirelli P6 (crap!! but big dia) on the rear (would need to check to be 100% sure)

Gross weight would have been about 1350-1400kg I would think with 2 persons and fuel.

Only got one run (with a passenger) as it developed a slight oil leak which concerned me (turned out to be a loose oil gauge feed pipe) but I suspect on the day it would have max'd out in the low 190's given the distance available. (removing the BMW Mini mirrors, taping seals and removing wiper would probably have added 2-3mph too)

The braking was fine, stable and sure and no ill manners.

 

[Rick Muck- Mark IV]

Just to add my 5c, I've driven Roy Smart's...

Wow....never knew a "Smart" car would go that fast!!!!

 

[Ian K]

506 hp and 431 tq. Very nice.

I have read that Gordon Levy does magic with 306 and 331 cubic inches.

I hear he makes a 8000 rpm, 500+hp 306 that doesn't stop pulling at any speed. Why did you choose 331 cubes?

I recall Gordon writing about his experience driving a GT40 that had one of his 306 motors in it with 8 stack EFI and reported it sounded like an F1 car. The induction noise was shocking.

Did you notice at 150-181 mph the steering getting light from front end lift? This has been a common complaint.

Gordon also has an awesome 351W displacing 355ci which is a detuned race engine. Output is 530 hp and 450 lb ft of torque. 7500 rpm shift point with a 7800 rpm rev limit. RPM limit can be raised, as can power. He also has/had a destroked 351W displacing about 317ci (IIRC), which revved over 10K (I believe the shift point was 9 - 10K). Produced somewhere around 700HP. He also makes a 331 race engine, 8500 RPM, 600HP and 550 lbs/ft.

Ian

 

[EGLITOM]

506 hp and 431 tq. Very nice.

I have read that Gordon Levy does magic with 306 and 331 cubic inches.

I hear he makes a 8000 rpm, 500+hp 306 that doesn't stop pulling at any speed. Why did you choose 331 cubes?

I recall Gordon writing about his experience driving a GT40 that had one of his 306 motors in it with 8 stack EFI and reported it sounded like an F1 car. The induction noise was shocking.

Did you notice at 150-181 mph the steering getting light from front end lift? This has been a common complaint.

My engine displacement choice was based on Gordons reco. My request was that i wanted to have decently reliable screamer, able to rev to 8000 because i wanted the sound of a high revving V8. The power output and displacements size wa than just a result of the choosen components.

The engine is running strong although i think that not all of the horses are there. For one it is still running a bit rich and the header size of 1 1/2" may comprimise top end power as well. So my guess is that i´m still missing some 30-50 Horses all over the band.


As noted before i can not tell any lightness in the steering. That said the steering is easy at every speed . Who ever asks for a servo steering in that car would spend money for nothing.

TOM

 

[William Quantrel]

Tom,

Sounds like Gordon gave you a power plant to reach 200 mph and Fran gave you the chassis to do it in and Henry Ford's boys gave you the aerodynamics.

Think your gearing would take you out to 200? Is there enough Autobahn to reach it?

You would be the first.

 

[Sam McDowell]

Here is a lift/drag chart from '08. I figured 220 lbs lost on the front @ 150 mph.ound on this forum in '08

 

[Warren]

Need a bit. Of advice, my Superformance GT40 Mark 1 gets front lift from around 200km/hr. Ride height is 4" front 5" rear and had a panel put in along the bottom of the front airscoop blanking off the gap between the bodywork and bottom of the radiator to force more air into them otherwise nothing unusual re suspension etc. Anyone experienced something similar?

 

[roaldin]

Which nose, single or twin nostril?

I use single nostril FWIW.

Excuse my ignorance but which front wheel arch profile do Superformance use on their mk1, the lower mk1 or the higher mk2?

Tim.

 

[Warren]

It's a Mk1 front, whole body if faithful to the original with the single nostril, lowering the front even more is still an option to keep the nose planted and avoid any wandering at high speed. Any set up advice would be appreciated, cheers, Warren.

 

[René]

tire pressure and a bit toe in (lining) could also have influence (or how you say that)
otherwise maybe ad some flaps (penguin style )>>