StarionX

I'm curious about engine speeds and internal stresses. Assume, one particular rpm point (in this case, 3000rpms). Does being at this point in ANY gear cause exactly the same stress in the engine, ie, 3000rpms in 2nd, and 3000 rpms in 4th.
Also, using this scenario, will the gas mileage be the same?

Thanks for putting up with a mechanical moron.

scathcart

I don't think its that easy, and way out of my level of techno-babble.

as for gas mileage... are you trying to state that the gas mileage in 3rd gear at 3000 rpm would get the same as in 4th gear at 3000 rpm? Well... theoretically, it should, right? The engine moves the same amount of air at 3000 rpm in 3rd as it would in fourth. However, you have to take into account forces on the car. Air friction is huge at those speeds. Cruising at 3000 rpm in fourth, the engine will move more air and make more power to sustain 3000 rpm than it would in third. As well, at higher speeds, the car becomes more and more unstable. The air lifts the tires on the front and rear a little bit more and more, and coupled with the vibrations of the car, decreases the amount of Friction force. AT WOT throttle, at the same rpm, same boost levels, in any gear, the fuel economy should be the same... but who cares about fuel economy at WOT?

As for engine stress... really, in engines, internal stresses go up due to inertia and momentum as engine rpms go up. As well, obviously, in higher gears, there is more mass to move, and thus the engine has more stresses in the opposite direction of rotation. Really though, forces in the opposite direction help stabalize the engine. You're much more likely to break a critical engine part at 7000 rpm in 1st than you are in fourth.

I'm sure that was mostly the obvious....

SureShot

It's simple: more power = more stress.
Power = RPM x torque.
Since torque (at WOT) is relatively flat above 3k in a Wankel, stress can be roughly proportional to revs.

SureShot

In trying to keep it simple, I left out the time factor. Basically, you are not in first very long.

SureShot

If you want a real stress test, a full run at WOT in 4th will not only string out the car, but also your heart rate, and your passenger's.

Samps

Gas milage in 4th will almost always be better than 3rd due to gearing. If the motor is spinning at 3k in third lets say the car is going 40 mph (no time for math); now in 4th gear the car is going 60 mph at 3k; so you will get more miles of distance at 3k in 4th than you will at 3k in 3rd. Do you understand what I'm trying to say?

scathcart

Actually, Power (hp) = (Torque (lb ft.) x RPM) / 5252. Thus, at 5252, the engine makes as much hp as it does torque.

Your math works out to the stock NA engine making like 60000 hp at 4000 rpm. It'd be nice, but not true.

scathcart

I think he knew this, but was asking about how much fuel the engine would use for a set rpm, based on gearing.

I mean, c'mon. NO ONE is stupid enough to think that 3rd at 3000 rpm and 5th at 3000 rpm would get you the same mpg... are they?

Samps

I have learned to never "OVERestimate" another humans knowledge. Most people, maybe 90%, are dumb. I'm not saying this guy is dumb; but in the few short years I have lived, I've noticed there are far more uneducated people.