633 replies to this topic

[Border Reiver]

I am pretty sure it is because the Mk I was a road car (and also has a smaller and less powerful engine), whereas the Mk II and Mk IV were racing cars and both have the larger, more powerful engine. With that much torque, there really was no need to put a five speed into it as it will pull quite happily in most gears. Presumably using a four speed box they could also make it stronger for the same overall weight and so found it to be more reliable for dealing with the available power?

Interestingly, the Chaparral only uses a 3 speed, again for similar reasons that it has so much torque from its 7 litre engine. As an experiment during beta testing, we did try the Chaparral with the smaller engine from the Lola and a 5 speed box, and the tests seemed to show that it was quicker that way, certainly for tighter tracks like Brands where you change gear more often.

Rob

[Lee200]

I believe Rob is correct.

Smaller engines with less torque/horsepower typically need more gears than relatively bigger engines.  One of the major benefits of more gears is that the engine can be kept in its peak torque/horsepower range longer.

The Achilles heel of the MkIIB was its transmission which failed miserably at the first race at Daytona in 1967.  Apparently, this was not because of the transmission's design; rather it was an improperly manufactured part which failed.  I'm pretty sure the MkIV used the same transmission as it had the same engine.  By the next race at Sebring, the faulty part had been identified and fixed.

The Chaparral was an interesting experiment.  I seem to remember that the reason they used a three speed transmission was that it was the only version available at the time that could handle the torque.  I'm not sure about this though as the Chaparral transmission was really a hybrid of a torque converter coupled to a manual transmission so you'd think there would have been a four gear manual transmission available too.  Certainly a four or more gear transmission would have been better though.  Jim Hall was no fool so he certainly was using the best transmission he could get for the job.

[Border Reiver]

Hi Lee,

It does make me want to find some time and dust off that Excel acceleration / gear tuning sheet I was playing with before. I suppose the choice of box does come down to the peakiness of the engine. In the 65 mod a lot of cars have 6 speed transmissions since the engines have narrow and pretty high rev range power bands and so, as you say, with more gears it is easier to keep the revs up in that range for optimum acceleration. With loads of torque available in a relatively low revving engine like the 7 litre blocks in the Chaparral and the big Fords you can pull from around 2000 rpm in almost any gear and it will simply cope with it, and so three or four gears is enough to ensure the revs never fall out of the power band during acceleration as you change up gears, and in fact having more gears available becomes a hindrance rather than an advantage. (With the Excel sheet this would actually be a very easy "thought experiment" to simulate and test).

A big advantage of having fewer gears must be that in the same available space/weight you can make the gears and shafts proportionately much thicker/larger and so more robust, which when dealing with large torques will be all important for reliability.

Rob

[Lee200]

Makes sense Rob.

If memory serves, Hall had a 2 gear transmission on the some of the original Chaparrals so a 3 gear transmission was a step up.

Wonder, as you say, if it was a size/space available consideration that prevented him from using 4 gears?

I believe Chevy automatic transmissions from that era were limited to 3 gears, but from my readings, it seems that the Chaparral used a normal manual transmission rather than an automatic transmission with the automatic feature removed.

There isn't a lot of info available as Chaparral kept their "secret" transmission pretty close to the vest.

[Lee200]

Went back and read my notes on the Chaparral and the first Chappie 2A (circa 1963) used a one gear transmission!  Hall said the torque to the wheels was so great due to the large engine and torque multiplier effect of the torque converter that it could spin the tires from 10' after the start until 80 mph using the then current racing tires.  So there was no need for a multigear transmission as available torque was more than the tires could handle.

As the racing tires improved in later years and had more grip, it made sense to add more gears to increase the torque.

Edited by Lee200, Jul 04 2012 - 11:59 AM.

[Larko29]

Thank you Rob and Lee for your responses

I actually took the Mark IV for a drive last night, and it is deceptively quicker than it seems 1 second slower than my best sector time in the Mk1 through a twisty section of track. Of the 2 I prefer the Mk1 and its more peaky nature, but you can't discount the benefits of a 7.0 litre engine and the associated torque it can generate.

I read up on the MKIIB on the Nostalgia Forum which was an interesting read also.

Craig

[JCarvalho]

Regarding the Chaparrals, the reading I've done says that during development, Hap Sharp was talking with Jim Hall and said: "Why do we need four or five gears? It burns rubber in all of them." The cars were very light and the engines VERY torquey. Two speeds were more than adequate until tire technology started to catch up with their aero and weight technology.

Jim

[sky]

well if you just look at the power to weight ratios - i think i have posted somewhere in this thread, the chaps are in a class of their own. they were the lightest cars and were also among the most powerful, if not the most powerful cars of the season per se. and as you know sometimes it is faster to not shift as much but to let the torque do it's magic. i feel that the chaps are well suited for fast tracks. on the slower ones, i would like to have an additional gear. but then you have to remember that the Chap 2D had won the 1966 race at the mighty green hell. and at that time it only had 2 gears and still came out on top. so the missing gears couldn't really be as crippling as it feels and torque goes a long way (which is why i'm currenlty shooting for a >500nm engine with 3.0l engine with only 231 bhp)  

[Lee200]

JCarvalho, on Jul 04 2012 - 09:16 PM, said:

Regarding the Chaparrals, the reading I've done says that during development, Hap Sharp was talking with Jim Hall and said: "Why do we need four or five gears? It burns rubber in all of them." The cars were very light and the engines VERY torquey. Two speeds were more than adequate until tire technology started to catch up with their aero and weight technology.

That's a great quote Jim.

When we were working on the Sports Car mod, I did a lot of research into how torque converters work and was surprised to learn that not only does a torque converter allow the engine to idle while the car is at rest, it also multiplies the torque just like an extra set of gears.  Typical torque converters can multiply the engine torque by 2.5 times at lower rpms.  Couple that to a transmission and then a differential which also multiply the torque and you can see why the tires couldn't handle it.

As Crag said, the Nostalgia forum is a great place for historical info too.

[Border Reiver]

Larko29, on Jul 04 2012 - 08:57 PM, said:

Thank you Rob and Lee for your responses

I actually took the Mark IV for a drive last night, and it is deceptively quicker than it seems 1 second slower than my best sector time in the Mk1 through a twisty section of track. Of the 2 I prefer the Mk1 and its more peaky nature, but you can't discount the benefits of a 7.0 litre engine and the associated torque it can generate.

I read up on the MKIIB on the Nostalgia Forum which was an interesting read also.

Craig

The Mk I should be an easier drive in the sense that it was firstly a road car, but was then also a customer car and so it doesn't make good business sense to make a car that the customer cannot drive. It actually has a very nice chassis, handles relatively well and has a nice balance, just that for its weight it is quite underpowered compared to most of the other cars in the mod. The Mk II and Mk IV were all about winning Le Mans which Ford became obsessed with in the 1960s. They don't handle all that well in relative terms, but on the reverse side of that, they also are 10mph (or more) faster than anything else down Mulsanne Straight. IIRC the Mk I is also capable of around 200mph (just like the Lola, P4, Chaparral and Mirage which is itself a Mk I GT40 variant), but it takes a long straight and a relatively long time to get it wound up to that limit.

Interestingly, once the rules changed in 1968, with different capacity limits for prototype and production cars, and the fun and games with how many cars were needed to be called a "production car", Ford went back to the Mk Is and won Le Mans again with those twice. There was also a Mk III as well, but that was only ever a road car IIRC.

For those who are interested, this: http://en.wikipedia.org/wiki/Ford_GT40 has some good background on the various GT40 variants and the development of the cars.

Rob

Edited by Border Reiver, Jul 05 2012 - 08:01 AM.

[gliebzeit]

The Ford GT40 Mk I was a purpose-built racing car.  The Mk III was a road-going version, made in limited quantity.

From the wiki entry:

The Mk III was a road-car only, of which 7 were built.[1] The car had four headlamps, the rear part of the body was expanded to make room for luggage, the 4.7 litre engine was detuned to 335 bhp (250 kW), the shocks were softened, the shift lever was moved to the center and the car was available with the steering wheel on the left side of the car. As the Mk III looked significantly different from the racing models many customers interested in buying a GT40 for road use chose to buy a Mk I that was available from Wyer Ltd.

Edited by gliebzeit, Jul 22 2012 - 09:45 AM.

[Border Reiver]

OK, fair enough, strike the road car bit about the Mk I, even though it got used that way. It was still smaller engined and sold as a customer racing GT car, whereas the Mk II and Mk IV were rather more specialist machinery made for the purpose of winning Le Mans, which was the point I was making about why the Mk I is much more friendly than either of the bigger engined GT40s.

Rob

Edited by Border Reiver, Jul 22 2012 - 04:42 PM.

[Jochem]

Hi,


I would like to thank you for this great mod and to make gpl always a good challenge to drive. However, although I had no problem to play with LPG 67Gt until today, it is impossible for me to configure the G25 again. Indeed, when I accelerate, it is the gearbox which is sought. What can I do? Do you know this problem? I should add that I have no problem with mod 65/67/66, etc. ...I'm using GplShift and it works fine with 65/66/67/69 mods.

[Bob Simpson]

Do you have automatic shifting selected in Options in GPL selected?  Also in Training mode, make sure that you have Prototype selected as the car in the track selection menu.

Whenever you create a new driver, all driving aids are selected as well as the basic trainer car by default.

[Jochem]

Bob Simpson, on Oct 03 2012 - 05:23 AM, said:

Do you have automatic shifting selected in Options in GPL selected?  Also in Training mode, make sure that you have Prototype selected as the car in the track selection menu.

Whenever you create a new driver, all driving aids are selected as well as the basic trainer car by default.

Everything is back ! How do I have forgotten, after all these years to practice GPL (since its release)  that there are options in menu ! XD

Thanks a lot Bob