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Originally Posted by Chris Melia Hi DBLDrew
and thanks for your comments this is exactly the type of discussion I hoped to promote. As I previously said the ZFQ can be supplied with different gear sets and final drive ratios, below is the table with a final drive of 3.77 giving a cruising speed of 87mph at 3000 rpm and 189 mph top speed at 6500.
In reality I acknowledge that the GT40 is a 200MPH car but it runs into an aerodynamic brick wall at around 165mph even Roy Smart with 500 Bhp on one of the longest airstrips in the UK had trouble going 170 Mph +. A professional driver driving an original GT40 at this years Le mans classic said that now the Mulsan straight had checains installed that his decision to run the 3.7 final drive was the wrong one! and that next time he would run the 4.2.
I doubt that there are many people on this forum that would ever get the opportunity to exceed 170 Mph.
The choice of which final drive and gear set is still up for discussion and I welcome further comments on this as we need to come to a decision in the next seven days on this for the first 25 transaxles to be manufactured.
regards
Chris.
Differential: 3.77
Tire Diam: 26.9 PERCENT DROP FROM
1st Gear: 2.30 DROP 6500 RPM
2nd Gear: 1.54 0.670 4352.2
3rd Gear: 1.14 0.740 4811.7
4th Gear: 0.90 0.789 5131.6
5th Gear: 0.73 0.811 5272.2
SPEED IN GEARS (MPH)
RPM 1st 2nd 3rd 4th 5th
1000 9.2 13.8 18.6 23.6 29.1
1500 13.8 20.7 27.9 35.4 43.6
2000 18.5 27.6 37.2 47.2 58.1
2500 23.1 34.5 46.5 59.0 72.7
3000 27.7 41.3 55.9 70.7 87.2
3500 32.3 48.2 65.2 82.5 101.8
4000 36.9 55.1 74.5 94.3 116.3
4500 41.5 62.0 83.8 106.1 130.8
5000 46.1 68.9 93.1 117.9 145.4
5500 50.8 75.8 102.4 129.7 159.9
6000 55.4 82.7 111.7 141.5 174.4
6500 60.0 89.6 121.0 153.3 189.0 |
I understand what you are saying about most people not ever going to be able to go over 170mph. That is true, and for a pure racing standpoint having the lower geared trans makes a lot more sense. But what is your target here? Are you trying to make a street trans or a racing trans? My guess because this is a helical geared, synchromesh gearbox, it should be geared (no pun intended) towards street use. Most people that would use your trans would probably spend the majority of the time on the street, and maybe hit the track a few times a year. Someone who is making a dedicated racer would go with a straight cut dog box anyway.
Just to continue to fuel the debate, if we look at the Transaxle for the Ford GT.
Ford Racing Performance Parts [M-7003-GT*]
The ratios are..
1st – 2.611
2nd- 1.708
3rd- 1.233
4th- .943
5th- .767
6th- .625
Final Drive is 3.36
So getting back to your point that most gt40s won’t have enough power to push it much past 170mph so why bother gearing it to 200.
Well again lets look at the Ford GT, A true 200 mph car. The Ford GT has 315/40 ZR19” rear tires that have a diameter of 28.9” So using the 6500 rpm in 6th gear we get a theoretical 266mph top speed. Obviously it’s not that fast it tops out a little over 200. Which buy the way is in 5th gear. 5th gear at 6500 is 216mph. So on a purely performance category 6th gear is completely useless. But having the ability to cruse on the highway with very low rpm is very attractive for a street car, especially if you are running a stroked motor.
If you build a Cobra and want to make 500-600hp, no problem just build a 383-408 stroker motor and with a Tremec t56 behind it, you won’t be screaming on the highway. It would be nice if we had that same luxury for the gt40 world.
I do like the 3.7 final drive better, but I still stand by my original post where it should be geared to do 200mph. There is also something that is very exotic about driving a true 200 mph car. Who cares if it never sees it, that isn’t the point.