Bill Lewis; you are correct that the 4.0 six seems to handle 2000rpm in OD
without complaint or "feelable" stress. Reason is, you have a relatively
large engine size and not only that, your engine is cammed to develop full
torque down low. Probably not max torque at 2000 (more like 2800) but none
the less, it has ample torque at 2000 and if the road is level, wind is not
from the front and load is not excessive...she rolls along nicely with
partial throttle opening and only slightly less than max fuel economy.
Due to lack of aerodynamics, you body will demand much higher hp production
to increase from say 50 mph to say 65mph than would a slick sedan or coupe
body. Example: a Porsche 911 body shape requires approx 30 hp to propell
at 60 mph. Your Jeep likely needs about 45 hp at 60mph. And BTW, this
difference gets disproportionately WORSE as speed goes up. I would guess
the Porsche needs about 90 hp at 100mph and your Jeep needs about 170hp at
100mph.!!!Go figure.
The Alpine size engines are SMALL and are cammed to produce peak torque at
3200 rpm. When they are lugged down to say 2000 and are in OD, they simply
have nothing in the way of extra torque to give. Of course, the car still
rolls along and the driver may not be aware he is causing internal strain
in this engine...but thats whats happening.
------------------
Dick S.; If you can drop by a major size tire dealer or distributor, he
will have a spec book from the Tire and Wheel mfrs. assoc.
This neat book (among other great data) gives the number or revolutions per
mile for all tire sizes. The figure assumes normal wheel, inflation and car
weight.
Lets say you tire makes 700 rev per mile in the spec page.
700 X your 3.89:1 axle ration = 2723 engine revs per mile.
Now we all know a mile per minute is 60 mph, so if you drive a measured
mile at 2723 engine rpm you should cover that mile is exactly one minute !
You say your tach has been checked as being OK. Was that done at both high
and low readings? Was it done on a master tach which itself was known to
be virtually perfect? I have doubts you could have done this yourself
unless you had an expensive shop size Sun, Snap-ON or other multi thousand
dollar digital tach to use.
I'm not saying any of your data was wrong but since I don't know your
personal situation I only suggest that there might be some degree of error
and having things check out on master gages would worth it.
----------------
Back in 1937, a supercharged Cord V8 set the USA speed record (AAA ran
things in those years) at 107.5mph
This was finally broken in 1953 by a Dodge red Ram coupe (V8 Hemi) at
110mph, again timed by the AAA.
Reason I am relating this bit of history is....from 1937 to 1953 no US
model could beat that Cord record but lots of owners thought they could. I
met all kinds of men (no ladies) who bragged about their high speed runs in
various cars. My boss at Buick had a 49 Roadmaster 320 cu in. and told of
120 on the speedo. Another friend told of his Kaiser Manhattan bumping the
needle at 125 or some other silly number. I could recite endless tales of
owners of everything from model A's to Cadillacs, which claimed speeds far
higher than the car would ever see. I recall a new 53 buick special I
owned which always was able to show 115mph. Once in the Buick engineering
dept at Flint, I was shown some performance data on 1967 models and asked
if they had it for my old 53 model. Sure they did and the proving ground
figure showed my exact car capable of an honest 94mph !
Magnetic speedos may be right ON at city speeds where cops give tickets for
a 40 in a 30 zone. This same speedo gets wild at high speeds and lies like
you wouldn't believe.
There is NO fix. Speedo shops cannot make it right at both ranges.
Electronic tachs are much more accurate and Rootes are about as good as any
others of that era. Still errors happen for various reasons .
Let us know if you ever check out your tire revs per mile and your tach
accuracy. We will all enjoy the report.
Dick T.
This archive was generated by hypermail 2b30 : Tue Sep 05 2000 - 09:56:46 CDT