Steve,
Just a few comments to add to the good info Laifman posted. First, regarding
a 5-speed vis-a-vis the rear end gears; your engine will not be happy in
fifth gear with the 2.88's. There are some choices of fifth gear, which is
an overdrive gear, but you want one around 0.75. In round numbers, say with
the stock setup your motor turns 2800 rpm at 70 mph, with the 0.75 overdrive
fifth gear, it would only be 2100 rpm. Another way to look at this is, at
5000 rpm you will be going 167 mph. Since this borders on the absurd, you
can see that the only use for fifth gear with 2.88's is for economy.
However, the motor you describe isn't going to run well at such low rpm. In
fact, the equivalent of 2.88 gears is, if anything, even too tall. Many,
many Tigers have opted for lower gears, and not just because of the first
gear close ratio problem. They just want to have the throttle response at
highway driving speeds and get better use of the four gears throughout their
personal range of "normal" driving speeds. To get the equivalent of the
2.88's with a 0.75 fifth gear you need 2.88/0.75 = 3.84. You can adjust the
math for the particular fifth gear ratio you use. If you were after getting
the top speed possible out of your Tiger, then with some more complicated
math we could pick the right final drive ratio based on the rpm where your
motor's horsepower output is a maximum, which I would guess in your case
would be in the range of 5500+ rpm. Your motor should be able to get to
about 140 rpm with proper gears. You can see that the 2.88 final drive ratio
is a good match to this; i.e., about 5600-5800 rpm at 140 mph. (Not that you
would ever want to go that fast, right? But do get Z rated tires just in
case you ever want to try it.)
Regarding your "genuine" HiPo motor, you can check the block from the
casting numbers to see if the block really is a HiPo. However, the important
HiPo parts are the rods, main caps, crank, and dampener (probably in
decreasing order of importance). Many stock blocks have been converted to
"HiPo" by substituting some or all of these parts. While there is a common
belief that the HiPo block is different in some significant way, there is no
real evidence for this. HiPo parts are nice, but I would say that if you
don't run over 6000 rpm, then a carefully built and balanced non-HiPo motor
would be completely adequate. But, it is nice to have the margin of safety
that the beefier HiPo parts provide.
I hope this helps.
Brgds,
Bob
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