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hp = torque * rpm * constant
to keep it simple lets ignore the constant and units, we will compare 2 engine w/ exactly the same maximum torque, say 100
but engine 1 makes max torque =100@2000rpm and engine 2 makes max torque =100@4000
engine 1: power = 100 x 2000 = 200,000
engine 2: power = 100 x 4000 = 400,000
remember we are ignoring all units and the constant so the #'s are for comparison only
also remember that each engine has a torque curve at rpm above & below the indicated ones.
what will the percieved difference to a hypothetical driver?
engine 1 will have a lot of low end grunt it will pull strongly, gearing will only add to the pull, it will have a relatively low top speed unless the gearing is highly overdriven, this sort of engine doesn't need lots of gears 4 or 5 is fine
engine 2 will have relatively poor pull down low but w/ proper gearing can be made to pull through out the rev range as gearing is a multiplier of torque, the more gear choices the better ie 6spd is better than 4
It is better to have torque high in the rev range because then you can take advantage of it w/ gearing
Now you can make a fast diesel as Audi has done by having lots of torque at relatively low rpm but then using lots of overdrive gears, but by far the more usual race engine strategy is to make torque at higher rpm then gear it to suit.
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