ZFQ new proposed GT40 transaxle

[Russ Noble]

Originally Posted by Chris Melia

There has been much comment on the poor performance of the GT40's in the quarter mile speed events, seldom do they achieve better than 12 seconds in the quarter. I put this down to tall gearing and I think this is more relevant for a street driven car with the occasional track day.


Chris.

That is interesting Chris.

I've never seen a GT40 being dragged. Are you saying that first gear is too tall and they are slow off the line, ie bog down without getting wheelspin? Once you're rolling wit tall ratios you should be able to hold 1st, 2nd and 3rd to higher speeds which can't be all bad. Depends I suppose if the last gear you use is revving right out. Must vary from car to car and trans to trans, surely?

Maybe, should start another thread on drag racing a GT40?

Cheers

[Scott]

Originally Posted by Chris Melia

Hi DBLdrew

I also think that running the trans with a tall final drive like 3.4 would exert higher torque loads on the gears and could promote reduced life expectancy.

Regards

Chris.

I thought nobody drag raced the GT40 is because they were afraid to drop the clutch on a hard launch and risk breaking the trans. Will this new trans be suitable for a big block MKII?

[Steve Briscoe]

Chris -
Are you going to produce it in the US and price it in dollars? Or, will this be a UK production priced in pounds? If I'm not mistaken, it takes about $1.90 to buy one pound. Also, what type of warranty will you offer?

Thanks,
Steve

[Chris Melia]

Hi Guys

Russ, you have to see this thread re The Brighton Speed trials,
2006 Brighton Speed Trials The GTD Club attend every year.
For an event like the Speed trials a 4.22 is probably the best ratio to use with a taller gear set and 400 Bhp some clutch slippage off the line is required. If however you have 500 BHP then 3.7 would be fine

Scott the proposed trans has a capacity for 600 BHP and 550 Ft lbs of torque provided your Big block is rated under these maximum Figures then yes you can use this trans with a big block.

Steve, we are working with Quaife in the UK for the proposed transaxle and will therefore carry a Quaife warranty, it will be priced in $ close to that of the RBT.

Regards

Chris.

[jpkuehne]

I'd like to suggest the Manta Mirage guys would probably also be quite interested, (despite their generally being a GM based crowd...!!!)

[Graham Inchley]

Chris,

The ZF is a heavy box. Can the Q be any lighter?

Great work.

[BruceB]

Now I know why Quaife were a bit vague when I was talking to them at the NEC and also by phone the following week.
30 mph/1000 revs is a nice cruising speed for top gear for a road car but is not much use for racing except for a small number of circuits, but if there is a large choice of ratios or if they are easy to change it would allow people to spec the box for what they want.
There seems to be two different views with respect to engines for GT40's some going for high power/high revs and some going for high torque/low revs, this is why I think a wide range of ratios would be useful.

[Chris Melia]

Hi Guys

Graham. the weight of the trans is an issue we are looking at closely and should be able to design out some weight without the loss of strength.…

Bruce you are right on both counts, we need to come up with a good set of ratio's for the first batch of 25 then we will be able to then supply the custom gear sets. Choice of final drive at this stage will be 3.77 or 4.2 initially.

Regards

Chris.

[DBLDREW]

Originally Posted by Chris Melia

Hi DBLdrew

again interesting comments, we agree the sixth gear option is without merit and also note the Ford GT has 28.9" ZR tires, with this large wheel and tire combo the 3.77 final drive gives you a top speed of 203 Mph in fith gear at 6500rpm.

Well that is another option, but I didn’t know that you could run such a tall tire in most gt40s

The question is especially for guys that want to drive their cars on the street with the odd hill climb speed trial and track use, why not get the best functional use from the gear set?

I agree, but if the car sees road use 95% of the time then I believe that the design should lean more towards being more road friendly. But anyway most hill climbs they won’t go into 5th anyway, (and probably not even 4th) so I don’t think gearing more highway friendly will have much impact on the “weekend warrior racer”

There has been much comment on the poor performance of the GT40's in the quarter mile speed events, seldom do they achieve better than 12 seconds in the quarter. I put this down to tall gearing and I think this is more relevant for a street driven car with the occasional track day.

Well with drag racing the hole shot is very important, so if people are babying it to save the trans or to try to keep the tires from going up in smoke, then the E.T. will suffer a lot. I don’t think that having a low enough first gear is the reason most replica gt40s are not getting any faster then a 12 second ¼ mile.

It’s all about putting the power to the ground, and believe it or not having a lower gear ratio makes it harder to do that. Think about it this way tack it up in 1st gear and dump the clutch, what happens? Well if you don’t blow up your trans your tires go up in smoke. Now tack it up in 4th gear and dump it (both from a dead stop) and what happens? Well you would probably break something, maybe burn up a clutch, but even if you managed not to break anything you won’t be spinning your tires. So anyway back to my point, if you are spinning your tires in first gear, lowering your gear ratio will only make it easier to spin your tires.

Bottom line is unless those guys are running Drag Slicks where they are maximizing grip, then having a lower gear ratio isn’t going to help them much for the ¼ mile.

I also think that running the trans with a tall final drive like 3.4 would exert higher torque loads on the gears and could promote reduced life expectancy.

Well then wouldn’t I have the same problem with running the taller tires like you suggested? After all the true Final Drive ratio is in fact the tire diameter. The problem with going with such a tall tire like the Ford GT uses is getting it to fit and having it maintain the 60s look that so many want to maintain.

I really think you should offer a few more choices on your final drive. Just search through the threads here looking at how many people have talked about custom ring and pinion (crown wheel and pinion for those across the pond) for the Audi, and Porsche transaxles, or the custom 5th gear options. I think there is a lot of people who want a more streetable trans and not having options for them might be a big mistake. If you want to keep just having 2 final drive options then maybe split the difference like going with a 3.90 and maybe a 3.50 for instance.

[Ron Earp]

Originally Posted by Chris Melia

There has been much comment on the poor performance of the GT40's in the quarter mile speed events, seldom do they achieve better than 12 seconds in the quarter. I put this down to tall gearing and I think this is more relevant for a street driven car with the occasional track day.

Having discussed this many times for lots of UK people I'd put it down to issues at Brighton, where you guys are pulling the times from. The place has horrible traction and is not a drag strip - it is a very old public road in a sandy area.

By contrast, everyone on this side of the pond is comparing proper drag strip times and they are naturally going to be better than the Brighton times in the UK. Strips are sticky, very sticky compared to streets. Drag strips in the US are all over the place, and, lots of people in the US know how to get a car to behave on a drag strip. Remember, we only like to go around in circles or in straight lines?? I know some of those 40s I've seen and be in over there would be 11 sec cars over here in the US with some slicks and good traction, no doubt.

Sorry to digress, back to your transaxle discussion. I don't think the short ratios are a bad thing at all, but I know that is an opinion driven. I'm gearing my car so that at about 175mph or thereabouts it is on the limiter in 4th, which is what I want for track work since I know where I will use the car. Seems that having some quick change sets might be a good idea, and certainly would make racers happy.

[Edit] - Looks like to me the box is about right on!

Ron

[Ian K]

You know, the originals ran well past 6500 RPM. I would imagine that with
the ZFQ's gearing, and 7000 RPM (or higher) will lift you into the 200 mph
arena (203+ according to the charts), and 7500 RPM will get you 207+.

Ian

[andys]

Chris,

Just for a point of reference, here are the Corvette Z06 ratio's. Keep us posted on your progress.

Corvette Z06
Gear Ratios
LS1/MM6 LS6/M12
1st Gear 2.66:1 2.97:1
2nd Gear 1.78:1 2.07:1
3rd Gear 1.30:1 1.43:1
4th Gear 1.00:1 1.00:1
5th Gear 0.74:1 0.84:1
6th Gear 0.50:1 0.56:1
Reverse 2.90:1 3.28:1
Diff. 3.42:1

Having run the dry lakes (El Mirage), it takes some serious HP to go 200MPH, but it's do-able. Aerodynamics helps a lot, and the GT40 seems reasonably good from that standpoint. However why one would want that kind of capability on a street driven car is beyond me. I would think a comfortable cruising gear or two would be plenty.

Andy

[Sandy]

Originally Posted by Ron Earp

... back to your transaxle discussion. I don't think the short ratios are a bad thing at all, but I know that is an opinion driven. I'm gearing my car so that at about 175mph or thereabouts it is on the limiter in 4th, which is what I want for track work since I know where I will use the car. Seems that having some quick change sets might be a good idea, and certainly would make racers happy.
Ron

I am with Ron, set the box up for 176mph at peak HP 188 into the limiter. The shorter the better unless just running a street car. Can't think of anyplace where I would need to go faster. The quick change for me is some smaller diameter tires, I think the Avons on my car are 27" now and you can go down 26" on a wider tire which move things down to 170mph and 181 into the limiter, I like that even better

Sandy

[Howard Jones]

A couple of things.

#1 1st gear needs to be low enough to be used as a stop and go traffic gear, pull it on the trailer ramps gear and, craw around the pits gear.

#2 Even if you end up with a 2nd gear ratio that doesn't quite fit the rev drop from 1st but is useful in the 30-50 MPH range then it will be just about right for most "slowest haipin corners" at most tracks. It will also be very useful as a good around the town 25mph - 45mph speed zone gear. About 2000-2500 rpm is nice and quite around neighborhoods and traffic cops.

#3 3rd and 4th are where the money is on most tracks. 3rd needs to be in the torque sweet spot at about 70MPH and pull to about a ton. Then 4th needs to get you right back to the sweet spot on the torque curve and run all the way up to about 145-150mph. With 400ft/lb of torque 3rd will work very well for just about any slow/medium corner. Down to 2nd is just another wasted shift most of the time. These cars have so much grip with good tires that you will find few corners that are slow enough for 2nd.

#4 5th, I use my car for fairly long freeway runs. Usually about an hour and a half at a go. Turn it around and run it home. The car is very happy at 80MPH and 2900 revs.

#5 6000revs @ .8ish 5th with a 3.4ish final will run a little over 170mph. It will take a LOT of power to get going that fast on any track out here on the west coast. Those speeds on the road.....well.... don't.

Assuming a SBF with 500HP and a good rev range of 3000 - 6750rpms gets me something like:

1st 2.70 Clutch saver
2nd 1.70 watch for cops nice and quite but punch at about 3600revs and you better hold on big fella!
3rd 1.35 It's gonna pull your head off with this one!
4th 0.95 and do it again all the way to a ton and a half!
5th 0.80 about 180mph and about 2800 @ 80mph. Just right.

Oh and its GOTTA have a QUAIFE diff!! friggin magic!!!!!!

Keep it under $10K all in and you got youself a winner.

[Gary Gibbs]

I have compiled and posted a gear chart that looks at a large array of transmissions and car combos. Link here: http://gt4d.com/trans_gears2.pdf All of the high torque V-8 cars on the market have tall gearing in 5th/6th gear. Look at the Ford GT and Saleen S7. The Saleen was the fastest tested 0-60 MPH production car by car and driver (3.3 secs).

I have purchased a ZF with tall gearing (purple line in chart) and am very happy with it. It has the same first gear ratio and last gear ratio as the Saleen S-7 just spread over 5 gears instead of 6. First gear is a bit tall for the parking lots, etc but great on the road and track. Mostly use 2nd-4th on track and 5th is for highway cruise. Since I can spin the tires at full throttle in first gear all the way up to 60 MPH having shorter gearing in first is not going to do me any good. But it is probably a good idea to see what the customers want and go that route. Just my $0.02

[Chris Melia]

Hi Guys

Thanks for your contribution so far its really interesting to get all this data feedback. I think that this thread may get post marked for future builders when trying to decide which trans combo they need.
Tables below for Pantera and original 289 GT40.
Engines developing around 350 BHP and similar torque, max revs - 6500

Weight of car – around 1200 kilos

Road use mainly with occasional track

Tyre dia 26.9 inch (Avon 295-50-15 V rated)

Typical ratios for a Pantera with a 4.22 CWP are :- 1st 2.23, 2nd 1.47, 3rd 1.04, 4th 0.846, 5th 0.704. Reverse 2.86. However tyre diameter was slightly smaller with the P Zero 335-35-15.

The original GT40 road/race car ratios were quoted with a 4.22 CWP as:- 1st 2.42, 2nd 1.47, 3rd 1.09, 4th 0.96, 5th 0.85. Reverse 3.75, and used a similar tyre dia. to that of the Avon.

regards

Chris.

[Paul Thompson 'Hooligan']

Sounds VERY interesting Chris - should give a boost to those wanting a good alternative to the somewhat less capable Renault/Audi standard options.

Re diffs, 3.44 is very popular in the UN1 and most competitors for Sprints / hillclimbs use slicks that are smaller in diameter to their normal road tyres which helps with the acceleration issues.

Dumping the clutch in 4th (by ERROR!) at Gurston resulted in a snapped drive shaft - the ONLY one ever broken on Roy's GTD (oops )

and trying a launch at 3000rpm in 2ND on slicks at Brighton resulted in:
http://www.gtd40club.co.uk/Videos/Light-em-up.wmv

Two normally aspirated GTDs have posted high 11s at Brighton now and have also achieved 136MPH+ on the quarter...

[Ross Nicol]

I found this article about gearbox/transmissions and it is interesting.

The balance of tractive effort and resistance is what should determine the ratios of each gear and the number to be made available.
In Brief
It may be said that the lowest gear ratio offered need be no lower than is necessary for a start to be made on the steepest gradient envisaged, nor any lower than would multiply the torque to the point where tractive effort would appreciably exceed the tractive capacity of the tyres, and of course it must be no lower than the maximum permissible stresses that the transmission can allow.
Top gear may be chosen according to any of a number of design considerations, but how many others should be offered between top and bottom, and what their spacing should be, will depend on the shape of the engines full throttle torque curve and the size of the production budget.
An engine that is big and flexible, with lots of back up torque and high speed asthma. may call for no more than 3 speeds. a small engine, or one with a torque curve rising to a peak at or near the peak power speed, may need five or six.

I have the Pantera ratios in my ZF which means a 2,23 1st with 4.2 C&P.
I find this gearing and the V8 torque really good for standing starts at the track and on the street its fine too. 5th at .7 has the engine revs at 3000 for 100k or 60mph (a little high).So if I was touring on the road I would prefer a 6th gear that lowered the revs to 2000.

Ross

[Chris Melia]

Hi Guys

taking your comments and trying to get close to optimum I came up with this chart

Differential CWP: 3.77
Tire Diam: 26.9 PERCENT DROP FROM
1st Gear: 2.50 DROP 6500 RPM
2nd Gear: 1.60 0.640 4160.0
3rd Gear: 1.17 0.731 4753.1
4th Gear: 0.92 0.786 5111.1
5th Gear: 0.74 0.807 5242.4
SPEED IN GEARS (MPH)
RPM 1st 2nd 3rd 4th 5th
1000 8.5 13.3 18.1 23.1 28.6
1500 12.7 19.9 27.2 34.6 42.9
2000 17.0 26.5 36.3 46.1 57.2
2250 19.1 29.8 40.8 51.9 64.4
2500 21.2 33.2 45.3 57.7 71.5
2800 23.8 37.1 50.8 64.6 80.1
3000 25.5 39.8 54.4 69.2 85.8
3500 29.7 46.4 63.5 80.7 100.1
4000 34.0 53.1 72.6 92.3 114.4
4500 38.2 59.7 81.6 103.8 128.7
5000 42.4 66.3 90.7 115.3 143.0
5500 46.7 73.0 99.8 126.9 157.3
6000 50.9 79.6 108.8 138.4 171.6
6500 55.2 86.2 117.9 149.9 185.9 FSB
7000 59.43 92.85 126.98 161.48 200.22 High revving motor.
7500 63.67 99.48 136.05 173.02 214.52 Hypothetical race motor

[Richard O'Clery]

Well done, Chris.

I'm watching both these threads with a great deal of interest, and I wish you every success. This is just what we need.