Since I
love my Lotus Elise, I don’t want to thrash it (so will avoid max RPM), but I
was curious to know if I’d be missing out on much performance by not thrashing
it. On Automobile Catalog there’s
this very interesting Horsepower
and Torque Curve for the Lotus Elise Sport 220. I’ve added on speeds for
1st/2nd/3rd/4th/5th/6th gear per 1000rpm, a red line above which we get 90%+ of max
torque, and an orange line
above which we get 95%+ of max torque.
It’s
interesting to see how fantastically flat (relatively) the torque curve is. The
90%+ line goes from around 2800rpm to
6800rpm. The 95%+ line goes from 3500rpm
to 6250rpm. Also, Horsepower is incredibly linear.
From scienceblogs.com:
Practically,
torque is a better measurement of how quickly your car will accelerate, while horsepower (relative to weight) is a better measure of your
car's top speed.
Note: In the below read “->” as “translates
to after changing gear”
So if I
always change gear at 6000rpm (rather than the 6800rpm max continuous engine
speed/7100rpm max transient engine speed):
1st gear
@ 28.5mph -> 2nd gear @ > 3000rpm
2nd gear
@ 52.74mph -> 3rd gear @ > 4000rpm
3rd gear
@ 76.8mph -> 4th gear @ > 4500rpm
4th gear
@ 103.8mph -> 5th gear @ > 5000rpm
So if I
always change gear at 5500rpm:
1st gear
@ 26mph -> 2nd gear @ ~ 3000rpm
2nd gear
@ 48mph -> 3rd gear @ > 3500rpm
3rd gear
@ 70mph -> 4th gear @ > 4000rpm
4th gear
@ 95mph -> 5th gear @ > 4500rpm
Since
3000rpm is within the 90%+ of maximum torque line, it could be argued changing
just after 5500rpm will give you an excellent acceleration, no need to tax the
car more (also, max torque is at 4600rpm, so changing at 103.8mph in 4th could
be argued as being too late - then again I might be talking rubbish).
Image: Lotus Elise Sport 220 Horsepower and
Torque Curve
It would
be interesting to work out the optimal speeds at which to change gear where the
torque curves intersect (i.e. torque has decreased in the lower gear to the
point where the higher gear matches it, so we can change to the higher gear to
get equal or better torque.)
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