Chris Thompson wrote:
> On another note, with the Tiger I'm much more interested in two blocks of
>rubber than 150 mph. The Stealth does the high end just fine, with a much
>smoother ride. Do you know anything about putting a 4.55:1 rear end in the
>car? It would seem that I need to pull both axles (special axles, according
>to the BOOK, although Norman can't tell me what that means), and possibly have
>to yank the whole rear end. Any advice would be appreciated. Thanks for your
>advice to date....
>
> Chris Thompson
Chris, and Tigers,
On your 4.55's. I am not sure whether you have a Mk I, IA, or a Mk II. The
usual reason people put those high numeric rear ends in is to get that low
speed thrust. It results, however, in very high rpm's at highway 4th gear
speeds.
If you were using, for instance, tires with a rolling diameter of 23.2 inches
(fairly common choice, and perhaps the largest you'd care to fit), here is what
would happen with your options:
Mk I, IA
2.88 gears @ 5000 rpm 52 71 93 120
4.55 gears @ 5000 rpm 33 45 59 76
Mk II
2.88 gears @ 5000 rpm 43 62 88 120
4.55 gears @ 5000 rpm 27 39 56 76
As you can readily observe, the 4.55's give you a lot of go in first gear, but
look at what happens on the freeway. Your doing 5,000 rpm at 76 mph, a fairly
common occurrence, and sure to drive you nuts.
The Mk II story is even worse, as you are out of first before your wheels have
stopped burning rubber. Well, you do get your black streaks, but they are not
very long.
But, look, side-by-side, at the comparisons between the Mk I (A) and the Mk II:
Mk I, IA 2.88 gears @ 5000 rpm 52 71 93 120
Mk II 2.88 gears @ 5000 rpm 43 62 88 120
If you really want a drive able car, and one that can take the power I am sure
you are going to put in that engine, I believe you are taking the wrong
approach. The 2.88's are a very good gear for the highway, allowing you to
cruise at an acceptable rpm, but the MkI and IA gearbox is totally wrong for
the car. Who want's to stay in first gear till over 50 mph. That's what is
making your take-off's so wimpy. A change to the 'wide ratio' Mk II gears make
an enormous
difference. There is lot's of push in all the lower gears, without a penalty
in high. I made the change by putting in a Mk II gearbox, but you can re-build
what you have to the Mk II gears, plus all new bearings, blocks and seals, for
less than $900 with someone else doing the work. much less if you can do it.
You are probably going to modify the engine, anyway, and that would give you
even more performance, without killing the car on the road.
My personal experience, on my Mustang conversion to a 5 speed T-5 "heavy duty"
version was a disaster. Aside from the fit problems, the fifth gear is chosen
all wrong for a sports car. It should be 0.8 in overdrive, Instead it's 0.63.
A 63% drop in rpm. Many think this is acceptable, and I agree - in a passenger
car, but it was chosen to meet federally mandated C.A.F.E. fuel economy
reasons, not performance. The gearbox, itself, is originally a Mazda derived
design, and
does not have much torque handling capability. A good engine breaks them up
regularly when the power is applied. I've seen stacks of them in the
performance transmission junk pile. This transmission is designed for about
300-400 ft-lbs of torque. The TREMEC, somewhat more, but even harder to fit. I
know, I looked at all of them for my Mustang and Tiger. Your top-loader is good
for over 600, and can handle anything you can get under your hood, including a
351.
Don't be fooled by the term "close" and "wide" ratio. It only means "closer"
and "wider" between these specific designs. The gears are evenly spaced in
both, but the "wide" ratio starts a little lower, which is what you want. The
major difference, to you, would be that when you shift gears at 6,000 rpm, the
close ratio changes 1,000 rpm (up, or down depending on which way you are
shifting). The wide ratio change is 1200 rpm. I am sure you don't think this
big Ford cares
about 200 rpm, at the top end. It is proportionally less, at lower rpms. My
son-in-law's '67 Mustang fastback VERY Hi-Po car had a close ratio set in it,
and he changed to the wide ratio. He couldn't have been more pleased, as was
I, on his advice. Who want's a 50-60 mph low gear?
If you want 'rubber streaks', I am also sure you don't want them in hops and
bumps, as your axle winds up. You can get this, with 2.88's and a wide ratio,
and moderate engine mods, but you better think about Traction Masters and a
limited slip differential. This reduces wheel hop, and side-to-side burns and
twitchyness.
This is probably longer than you, or I would have wished, but I've heard this
same issue so many times I thought I'd write up my own personal opinions on the
subject. Especially since I have actually done them, or (in the case of the
4.55's), had close personal relations and experience.
Hope this is of some help.
Steve
--
Steve Laifman < Find out what is most >
B9472289 < important in your life >
< and don't let it get away!>
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