Try spinning a Gyroscope, it has high angular speed, so it requires a lot of energy to change its speed in any direction, including just twisting it in your hand. if you play with it, you'll notice that the amount of force it takes to play with it in your hand is not directly proportional to the speed, but as speed increases, the force needed to move it increases at a faster rate.

 

The amount of rotational kinetic energy an object contains has no influence on the amount of torque necessary to accelerate the object. You are trying to apply a correct formula to an incorrect situation.

 

You are correct

 

I agree with mwatson184.

(torque) = (rotational inertia) x (angular acceleration)

As laundryhamperman stated, I is a constant. As torque increases, acceleration also increases. The relation between the two is linear (Fund. Physics 6th Ed. 11-9).

Wait, I just thought of something. Maybe someone's got their relativity theory mixed up? It's true that the amount of force required to accelerate an object increases with its kinetic energy, but only at relitivistic speeds.

 

You are referring to polar off axis movement which is not applicable to this discussion. An engine has a fixed axis of rotation. Unless you want to spin a RX7 360 degrees in the air, wile it’s running at top rpm. ...................HMMMMMM that might be kinda cool to watch.

Granted the whole car will rotate thought a corner. But the angle of rotation when a car is going though a corner is very small.

But for this discussion, we are talking about acceleration, in terms of an engine spinning up. Which is for the most part, solely controlled by Moment of inertia, and available power. (Setting aside parasitic drag and load)


Moment of inertia is not linked to any thing else other than mass and how far that mass is off of the center line of rotation. This is a FIXED value; it doesn’t matter if it spins at 100,000,000 rpm or 10 rpm. It will ALWAYS require the same amount of force to over come the inertia, and accelerate.

 

mmmm, another look..... torque = I (alpha)......Omega = Omega(initial speed) + (alpha)(time)......Omega = Omega(initial speed) + (torque/Inertial value)(time)....so the change in angular speed is proportional the torque times time......regardless of the initial speed....i understand better now. Good review guys, thanks for catching my mistake.

 

Your welcome glad to help

 

OMG my brain popped

 

Peejay, I guess you think all the Formula 1 guys don't know what they are doing by designing their engines to spin at 18,000 rpm.

 

A stock rotary with stock ports and a 3-liter V10 with incredibly hot cams and titanium internals are two completely different things.

I'd say don't bother going beyond the stock redline unless you've got a large side port or bridge/peri port on an NA, or a large single turbo (and porting) if you're a turbo...

Of course, I personally don't see much point to shifting *below* the redline, like some people suggest, even if max HP/torque is a bit lower than redline... since you want the next gear to be high in the torque band anyway...

 

There's a good read around here somewhere about shift points.....possibly its on nopistons. Its describes how to calculate your best shift points based on knowing the torque specs from a dyno and knowing your gear ratio's. The point of the story was to calculate the torque delivered to the wheels, and shift when when torqe in the next gear equals the torque delivered in the previous gear...

 

^that shift point also happens to be where the HP at the motor is equal before and after the shift.