i need a rundown on the differenced between the two motors. major differences, strong points, weak points, aftermarket parts availability?
the l98At The Drag Strip
Back to carland, and some examples of how horsepower makes a major
difference in how fast a car can accelerate, in spite of what torque on your
backside tells you :-). A very good example would be to compare the current
LT1 Corvette with the last of the L98 Corvettes, built in 1991. Figures as
Engine Peak HP @ RPM Peak Torque @ RPM
L98 250 @ 4000 340 @ 3200
LT1 300 @ 5000 340 @ 3600
The cars are geared identically, and car weights are within a few pounds, so
it's a good comparison. First, each car will push you back in the seat (the
fun factor) with the same authority - at least at or near peak torque in
each gear. One will tend to feel about as fast as the other to the driver,
but the LT1 will actually be significantly faster than the L98, even though
it won't pull any harder. If we restate the horsepower formula, we can begin
to discover exactly why the LT1 is faster:
Horsepower x 5252
Torque = -------------------------
If we plug some numbers in, we can see that the L98 is making 328
foot-pounds of torque at its power peak (250 hp @ 4000), and we can infer
that it cannot be making any more than 263 pound feet of torque at 5000 rpm,
or it would be making more than 250 hp at that engine speed, and would be so
rated. In actuality, the L98 is probably making no more than around 210
pound feet or so at 5000 rpm, and anybody who owns one would shift it at
around 46-4700 rpm, because more torque is available at the drive wheels in
the next gear at that point.
On the other hand, the LT1 is fairly happy making 315 pound feet at 5000
rpm, and is happy right up to its mid 5s redline. So, in a drag race, the
cars would launch more or less together. The L98 might have a slight
advantage due to its peak torque occurring a little earlier in the rev
range, but that is debatable, since the LT1 has a wider, flatter curve
(again pretty much by definition, looking at the figures). From somewhere in
the mid range and up, however, the LT1 would begin to pull away. Where the
L98 has to shift to second (and throw away torque multiplication for speed),
the LT1 still has around another 1000 rpm to go in first, and thus begins to
widen its lead, more and more as the speeds climb. As long as the revs are
high, the LT1, by definition, has an advantage.
Another example would be the LT1 against the ZR-1. The ZR-1 actually pulls a
little harder than the LT1, although its torque advantage is softened
slightly by its extra weight. The real advantage, however, is that the ZR-1
pulls another 1500 rpm beyond the point where the LT1 has to shift.
There are numerous examples of this phenomenon. The Integra GS-R, for
instance, is faster than the garden variety Integra, not because it pulls
particularly harder (it doesn't), but because it pulls longer. It doesn't
feel particularly faster, but it is.
A final example of this requires your imagination. Suppose we can tweak an
LT1 engine so that it still makes peak torque of 340 foot-pounds at 3600
rpm, but, instead of the curve dropping off to 315 pound feet at 5000, we
extend the torque curve so much that it doesn't fall off to 315 pound feet
until 15000 rpm. (All of the moving parts would be made out of unobtanium).
If you raced a stock LT1 against this hypothetical car, they would launch
together, but, somewhere around the 60 foot point, the stocker would begin
to fade, and would have to grab second gear shortly thereafter. Not long
after that, you'd see in your mirror that the stocker has grabbed third, and
not too long after that, it would get fourth, but you'd wouldn't be able to
see that due to the distance between you as you crossed the line, still in
first gear, and pulling like crazy.
I've developed a computer simulation that models an LT1 Corvette in a
quarter mile pass, and it predicts a 13.38 second ET, at 104.5 mph. That's
close (actually a tiny bit conservative) to what a stock LT1 can do at
standard air density at a high traction drag strip, being powershifted.
However, our hypothetical modified car, pushing no harder than the stocker
(at peak torque) runs an 11.96, at 135.1 mph, all in first gear. It's also
making 900 hp, at 15,000 rpm.
Folks who are knowledgeable about drag racing know that any self-respecting
car that can get to 135 mph in a quarter mile will just naturally be doing
this in less than ten seconds. Of course that's true, but I remind these
same folks that any self-respecting engine that propels a Corvette into the
nines is also making a whole bunch more than 340 foot-pounds of torque.
That does bring up another point, though. Essentially, a more "real"
Corvette running 135 mph in a quarter mile (maybe a mega big block) might be
making 700-800 foot-pounds of torque, and thus it would pull a whole bunch
harder than my paper tiger would. It would need slicks and other
modifications in order to turn that torque into forward motion, but it would
also get from here to way over there a bunch quicker.
On the other hand, as long as we're making quarter mile passes with fantasy
engines, if we put a 10.35:1 final-drive gear (3.45 is stock) in our fantasy
LT1, with slicks and other chassis modifications, we'd be in the nines just
as easily as the big block would, and thus save face :-). The mechanical
advantage of such a nonsensical rear gear would allow our combination to
pull just as hard as the big block, plus we'd get to do all that gear
banging and such that real racers do, and finish in fourth gear.
The only modification to the preceding paragraph would be the polar moments
of inertia (flywheel effect) argument brought about by such a stiff rear
gear, but that is outside of the scope of this already massive document.
At The Bonneville Salt Flats
Looking at top speed, horsepower wins again, in the sense that making more
torque at high rpm means you can use a taller gear for any given car speed,
and thus have more effective torque at the drive wheels. Finally, operating
at the power peak means you are doing the absolute best you can at any given
car speed, measuring torque at the drive wheels. I know I said that
acceleration follows the torque curve in any given gear, but if you factor
in gearing versus car speed, the power peak is it. An example, yet again, of
the LT1 Corvette will illustrate this. If you take it up to its torque peak
(3600 rpm) in a gear, it will generate some level of torque (340 foot-pounds
times whatever overall gearing) at the drive wheels, which is the best it
will do in that gear (meaning, that's where it is pulling hardest in that
However, if you gear the car so it is operating at the power peak (5000 rpm)
at the same car speed, it will deliver more torque to the drive wheels,
because you'll need to gear it up by nearly 39% (5000/3600), while engine
torque has only dropped by a little over 7% (315/340). You'll net a 29% gain
in drive wheel torque at the power peak versus the torque peak, at a given
Any other rpm (other than the power peak) at a given car speed will net you
a lower torque value at the drive wheels. This would be true of any car on
the planet, so, theoretical "best" top speed will always occur when a given
vehicle is operating at its power peak.
"Modernizing" The 18th Century
For the final-final point, what if we ditched that water wheel, and bolted
an LT1 in its place? Now, no LT1 is going to be making over 2600 foot-pounds
of torque (except possibly for a single, glorious instant, runnin