Gear ratios for the GT40 Mark IV?

[Ian B Anderson]

Sorry if this is in the wrong discussion, this is my first actual post besides the introduction post I've made on this site. I and another user on another forum discussed about the performance of the GT40 Mark IV on a game/sim we played and we both reached a conclusion that the car is performing incorrectly. The car can't reach the magical 212mph people talk about and in fact, with stock settings with how the game states, it can only go 197.

With some investigation we made the car as accurate as possible with data on this site and with the gear ratios listed by this site here. Our problem is that even several other websites quote the 3.09:1 final gear, yet mathematically, for the car to reach that 212mph number at 6200 RPM would be physically impossible as to hit that speed, the car would need about 8800RPM for the 3.09:1 gear ratio to work. The closest we've gotten to the 212 was using a 2.25:1 final gear and a 1:1 gear ratio for the fourth gear. After that, we were stuck. There's nowhere else to go and in my mind, I felt this was the best place to go for information on the GT40 Mark IV.

I guess this was a very roundabout way of asking if someone here knows the actual gear ratios for the GT40 Mark IV. I'll list my sources below, and thank you for anyone reading this.

SuperCars.net

Sportscars.net

GT40s.com Spec sheet

 

[Bill Kearley]

In a lot of gear boxes the top two gears are overdrive, as low as .6 to one. Gear set changes are made to suit a given track.

 

[Ian B Anderson]

In a lot of gear boxes the top two gears are overdrive, as low as .6 to one. Gear set changes are made to suit a given track.

The gear setup we were experimenting with is one for the 24 Hr Le Man. So far we haven't a sure-fire way to replicate that speed. Especially since the horsepower the Mark IV has, it would take 7900 RPM to actually hit 212 with the gear ratios that we experimented with.

 

[Jac Mac]

For the MKIV manual trans.
The 3.09/1 R&P was for the Auto trans. Manual used 2.5/1 1st 2.32/1, 2nd 1.69/1, 3rd 1.29/1, 4th 1 to 1.... Bear in mind the T44 had options in the QC gears for over/under/1 to 1 factors between the trans/final drive sections...

 

[Ian Anderson]

What tyre diameter are you using in your calculations? They ran 27 inch diameter in period.

 

[Kev Farrington]

Rings a bell that ratio. Ford Capri V6 road cars? I had a few and non of them would quite make those speeds.

 

[dick]

Quote from Mk 2 data records - "A Long 2-dry-plate clutch, each plate 10.0 inches in diameter, transmits torque to the input shaft of the gearbox; a production 4-speed synchronized gearset takes over from there, and finally a set of transfer gears takes the torque to the output shaft. It is the transfer gearset that is varied to give different final drive ratios: the differential ring gear and pinion are always the same at 3.09 (34/ II). In the case of the Le Mans Mk II. The transfer gearset is 0.899:1 for a final drive ratio of 2.77:1. The four gearbox ratios are 2.22, 1.43, 1.19 and 1.00:1."

 

[Jac Mac]

Quote from Mk 2 data records - "A Long 2-dry-plate clutch, each plate 10.0 inches in diameter, transmits torque to the input shaft of the gearbox; a production 4-speed synchronized gearset takes over from there, and finally a set of transfer gears takes the torque to the output shaft. It is the transfer gearset that is varied to give different final drive ratios: the differential ring gear and pinion are always the same at 3.09 (34/ II). In the case of the Le Mans Mk II. The transfer gearset is 0.899:1 for a final drive ratio of 2.77:1. The four gearbox ratios are 2.22, 1.43, 1.19 and 1.00:1."

Only problem with all that is the question related to the MKIV.

 

[Tom]

Does the above simulation account for tire growth?

 

[D. Nye]

Ian, You may want to find a copy of SAE paper 670071. This was the paper written about the Ford dyno setup they used to simulate the Le Mans Circuit. Drive shafts were connected to the dyno so no tire growth in these numbers. When building my Mk IV I worked the numbers until I got a gear ratio close. Some check points are Gear/MPH/RPM, 1/54/400,0 1/80,6000, 2/115/5100, 2121/6000, 3/115/4390, 3/121/4620,3/157/6000,4/57/5050, 4/162/5200, 4/195/6000,4/210/6200, 4220/6250. Hope this helps.

 

[Ryan L]

@jac mac did the MKIV run the same drive line as the MK II?

 

[Jac Mac]

As in a T44 ,yes, other than the two? automatic trans versions. One thing I've not been able to find out for sure is whether they ever tried to use the ZF behind the FE engines in the early testing stages of those cars.

 

[Ryan L]

Thanks Jac, I thought I saw the T44 in the MK IV, just wasn't up to speed with all the details of how it was set up.