Bob,
Nice letter. Gave a good overall thought to the issue. Here are some
numbers to chew on.
You missed a few issues. Although your recommended 0.75 would be nice,
it is not offered by anyone. The fifth ratio is 0.63 in he T-5 and the
0.68 in the TREMEC, which just makes what you said even worse. The
pre-C.A.F.E. design of an overdrive for performance was 0.8, which is
what the Alpines and Healys have. TREMEC will make one for you, but the
cost of the transmission doubles. There were some statements that Dale
A. had a 0.8 T-5 option, but I couldn't trace that down. (I guess I
could have called!, but wasn't buying). If so, it's the only one I've
ever heard of.
If you did go to a 3.84 (or whatever is close, the fifth would be better
- but this cure is like wearing rubber gloves because you have a leaky
pen. The numbers (for a more available 3.54, are below)
If you remember, you were surprised at the first gear ratio of 2.95 for
first, in the SVO Super Duty T-5 FOR-M-7003-Z (World Class). Here are
the rest: 2nd = 1.94, 3rd = 1.34, 4th = 1.0, and 5th = 0.63
For the Tremec TR-3550 (and they do have a more expensive one) the
numbers are 3.27, 1.98, 1.34, 1.0, and 0.68 ( a little better)
As you already know, the Mk I / IA are both 2.32, 1.69, 1.29, and 1.0,
while the Mk II is 2.78, 1.93. 1.36, and 1.0
Which is why the Mk II is so much better in the lower gears. I do
believe the 5 spds. would be too low in first, as the Mk II is damn near
perfect with the 2.88, and real stump pullers with the 3.84.
It's just a lousy choice. I've got all the numbers worked out on the
mph/1000 rpm with 23.2 inch tires (185/70/13), and they tell the story
pretty well.
If you shift at, say, 6000 rpm for the performance crowd, here are the
speeds you will be going with the various combinations.
Mk I / IA 2.88 gears (185/70/13 tires)
6000 rpm shift point
1-2 62 mph @ 6,000 rpm
2-3 85 mph "
3-4 111.5 mph "
4th 143.8 (lot's of luck {9->)
(23.97 mph / 1,000 rpm in high) Mike Taylor's book (p 223), with
original 5.90 x 13 23" tires puts this number at 23.92 mph / 1k rpm)
If you like this number, as it is easy to check calculated your speed in
any gear, just divide the numbers quoted throughout by 6.
Mk II 2.88 gears (185/70/13 tires)
6000 rpm shift point
1-2 51.3 mph @ 6,000 rpm
2-3 74.5 mph "
3-4 105.7 mph "
4th 143.8 ( never happen, unless your Team Tiger)
(23.97 mph / 1,000 rpm in high) Mike Taylor's book (p 223), with
original 5.90 x 13 23" tires puts this number at 23.92 mph / 1k rpm)
T-5 World Class 2.88 gears (185/70/13 tires)
6000 rpm shift point
1-2 52 mph @ 6,000 rpm
2-3 74.5 mph "
3-4 105.7 mph "
4th 144 mph ( never happen)
5th 228 mph (for Dr. Mayf, maybe - but his horsepower would have
turned this box into scrap metal. It's not very strong,)
The real story here is that you'd probably be out of 4th at 70 (3,000
rpm), and be turning 1840 rpm in 5th. In my opinion, I don't think
there is much torque available at that low an rpm to do anything put
cruise, with an immediate shift for any speed increase, or decrease. If
you slow down, you'll be at too low an rpm to get back up to speed in
any reasonable time on a freeway, and put a lot of strain on the
engine. That's why the automatics shift out of OD the minute you touch
the throttle.
Now, Just to please those who are considering a T-5 with 3.54 gears,
here's is where you'll end up:
T-5 World Class 3.54 gears (185/70/13 tires)
6000 rpm shift point
1-2 42 mph @ 6,000 rpm
2-3 61 mph "
3-4 86 mph "
4th 117 mph (should do this, if you can get 6,000 rpm, and a few mods)
5th 186 mph (yeah, sure!)
Your going out of second gear where a Mk I gets out of first!!!!
I gathered all this information, and made the calculations 5 years ago,
before I chose which transmission to use for my '66 Convertible Mustang
GT HiPo, but sold it to get the Tiger. They were re-done for the Tiger
tires and rear end, and I chose the Mk II gearing as the best all-round
solution for a street machine with occasional bursts of daring do, and a
little Auto-X.
I couldn't stand that long first gear on the Mk I, and the change to
the Mk II made the car come alive. Who needs 60 mph in first? The T-5
would give similar results, but the body mods, cost, and poor torque
capability of this Mazda original design made me choose the Mk II gear
set.
They will slip right in to your case, if you don't get a Mk II box. I
would recommend getting a newer case design, with the 8 holes, in case
you ever want a 6 bolt engine. It is identical, in other respects, and
you your Tiger output shaft and tail stock, so you don't have too much
trouble locating a core. Replace all seals, cluster shaft and bearings,
they are cheap, and any gear or synchro blocker that needs it. Remember
to use your original cast iron front bearing retainer, as it is a
smaller diameter than the later models. Keep the donor retainer for use
with a 6 bolt, as the bell housing has a bigger hole.
I know there are many opinions on this issue, but the gear ratio numbers
are just engineering calculations, not opinions, and so are the
published torque ratings of the various transmissions. I have the
Tremec gearing
Steve Laifman < Find out what is most >
B9472289 < important in your life >
< and don't let it get away!>
http://www.TigersUnited.com/gallery/SteveLaifman.asp
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