piston vs rotary engines!!??

[FYRHWK1]

Originally Posted by disco192

Well unless you are going slower than 15 mph i dont see why you would be in the bottom part of your powerband anyway.

And what you are trying to say is low end power, not torque. Torque does not accelerate a car, horsepower does.

Here's a funny thing though, throughout your gears, your horsepower stays exactly the same at any point in the powerband. Yet in lower gears, the higher torque multiplication accelerates you faster, as does adding torque from the engine, but if you ONLY add horsepower by revving higher (assuming your torque doesnt drop off too fast) then you dont accelerate faster at all, you just stay in gear longer.

[Polygon]

First, I'm not pissed. Second, the piston does have to fight the inertial forces on it and if you really want to delve into physics I suppose it does stop but for a nearly immeasurable amount of time.

Still, it is far more efficient than a rotary.

[kfoote]

Originally Posted by Polygon

First, I'm not pissed. Second, the piston does have to fight the inertial forces on it and if you really want to delve into physics I suppose it does stop but for a nearly immeasurable amount of time.

Still, it is far more efficient than a rotary.

So we can get this out of the way, I'll delve into the semantics of the physics of the internal combustion engine. All below are with respect to the engine block and negating the actual movement of the vehicle, and are true regardless of RPM (assuming nonzero RPM), change in RPM, or throttle input.

Position is constantly changing, and the rate of change of position is constantly changing.
Piston Velocity is zero at TDC and BDC, but the rate of change of piston velocity is constantly changing. The time the piston is stopped is 0, but there are two points where it is stopped.
Piston acceleration is zero at the midpoint of the stroke (this is only true for constant RPM, with changing RPM the location of zero acceleration can move slightly), but the rate of change of the acceleration of the piston is constantly changing. The time the acceleration is stopped is 0, but there is a point where there is no acceleration.

I hope that clarifies a few things.

Efficiency of an internal combustion engine is higher than for a rotary engine. Exactly why this is the case is beyond my knowledge base, a good indicator of this is the HP:Fuel Mileage ratio. A normally aspirated gen II RX7 makes about 160 HP and gets about 20 MPG, where a Porsche 944 is about 150 HP and gets about 25 MPG. A gen III RX7 Turbo makes about 270 HP and gets about 18 MPG, and a Nissan 300ZX Twin Turbo makes about 290 HP and gets about 20 MPG. There are a lot of other factors involved, but generally the efficiency for an internal combustion engine is around 20-22% and is about 18-19% for a rotary. This is all based on memory, so the exact numbers could be off, but the general idea is the same.

The problem with increasing boost in a rotary is the reliability of the apex seals. You do get a higher percentage gain in power and tourque for a rotary, but you can run more boost in a internal combustion engine more reliably than in a rotary.