SMYUEN said:
Tanzy,
Most importantly whats the shape of the power and torque curves?
Power curve should be as linear as possible and torque curve should be as straight (horizontal) as possible so you can get as near to peak torque at any RPM. (from my understanding lah...)
Hi Doc, a street engine is pleasant to drive the earlier the torque peaks. The ease of driving (power width) comes at the cost of pure power potential (hp/litre) of the engine.
The higher tuned an engine is, and/or the more flexible the gearing (more gears, or wide range CVT), the higher up the RPM range the torque peak is going to be. Some high tune street engines.. M3 torque peaking at about 5000rpm, Stradale around 5000rpm, S2000 around 6000rpm. In these cases it isn't so much a having-peak-torque-everywhere situation, but more one of having more and more torque the higher rev goes (hence power). Not less now, but a lot more later. The larger the displacement of an engine, the more comfortably you can get away with moving peak torque up the rpm range since the dispalcement will still inherently provide sufficient torque down low even as you tune away from it. With big engines on street tires you end up nuking the tires anyway which does nothing for acceleration, so might as move it up to provide more useful power later.
It is possible to go to either extreme - one being very early peak torque, severely compromised overall power, low stress, low fun engine - the other being very late peak torque, very high power but in too narrow a range, high stress, high fun (challenging to drive) engine that takes ten tenths to drive properly.
This all is subjective, but personally I consider sporty street engines to have the peak torque at least after the first 50% of the rev range - preferably after the first 55% of the rev range. Pure race engines even later...
