4x4ord wrote:
Hannibal wrote:
shepstone wrote:
I don't quite understand why max hp and max tq are both achieved at different rpm ? and with that which of the 2 rpm's should I be using to get the most out of an engine when climbing or accelerating with a heavy load?
Max horsepower will put the most torque to the rear wheels.
It kind of depends how you look at this question. Say you start climbing a hill with a big trailer. As the grade increases you floor it and your transmission drops two gears and the engine is running at near the rpm where it makes maximum power. The hill is long and getting steeper, you keep your foot to the floor but the engine continues to loose rpm; as it slows it continues to increase the torque to the rear wheels until it either meets the demand of the hill or the rpm drops to where the e.engine is making maximum torque. If the hill still demands more torque another downsjit is required and the engine increases its rpm again so it can start the cycle over again. Anyway you will pull the hill the fastest in the gear that keeps your engine revved close to the rpm where maximum HP is achieved but in each gear the rpm where the engine makes the most torque is always the rpm where the engine will pull the hardest in that gear.
So when a downshift occurs the engine revs higher where, although it may be making more HP, the crankshaft torque is likely lower.....the transmission gear ratio, however, more than makes up for the loss of engine torque and the rear wheel torque is higher. (Gears multiply torque) On page 8 I explained how HP and torque are both produced by fuel but how max torque is achieved at the rpm where the engine is most efficient (where the engine burns the most fuel per revolution) and max HP is produced at the rpm where the engine can burn the most fuel per time.
