jeeperxj91

If a V8 is putting out 2000 RPMs and a I4 is putting out 2000 RPMs also, wouldn't they be technically putting out the same power since the cranks are rotating at the same speed (lets keep the engine by itself and away from the rest of the drive train for the sake of the comparison)?

nicetie

Nope

Metmknice

Displacement is a HUGE factor in this discussion.

NeosXJ

An easy (but admittedly simplistic) way to visualize this is to imagine a single-cylinder weed-wacker engine spinning the same flywheel at 2000 RPM... It could probably spin it at the same speed as the V8 and I4, but would have way less power... Once a load (such as the weight of the car) is placed on it, the flywheel would stop spinning almost immediately.

You really can't gauge power or torque from RPMs alone: a rubber band can spin a toy propeller 2000 RPM, but the power (both HP and torque) is not even comparable to moving a flywheel with a larger displacement engine.

Hope this helps a bit!

mike37

jeeperxj91

I know this comparison I gave is wrong, but I want to know why. I was just thinking that if two different engines are spinning at the same RPM they are producing the same power also. Do larger engines have larger cranks, and therefore are turning something much larger at the same speed as an engine with a smaller crank (I feel like I am misunderstanding something about torque and displacement here)?

I guess I am also not thinking about the engines when load is added. An engine with a larger displacement will produce more power at the crank and will be able to turn the flywheel much easier than an engine with a smaller displacement correct?

mike37

RPM has nothing to do with torque and HP
its displacement and stroke
and type of fuel capability to use that fuel

mike37

think of it like a wagon
two horses on level ground can pull a wagon with 5000 lb at 5mph
four horses on level ground can pull a wagon with 5000 lb at 5mph

now start adding weight to the wagon
or going up hill
what wagon is going to be able to carry more weight
or go up a steeper hill

jeeperxj91

Yeah that is what I was saying in my last post, I wasn't thinking about any of this when load is added to an engine. Thanks for tolerating my stupidity, lol.