7 replies to this topic

[Magoo]

One more feature story based on a discussion in this forum: reverse-rotation engines for oval track racing.

Here we attempt to separate the truth from the legends in Smokey Yunick's 1959 reverse-rotation Kurtis-Offy...


Another Look at Smokey Yunick's Reverse Torque Special | Mac's Motor City Garage.com

[gruntguru]

Unfortunately this is one of those examples of Smokus Pocus. When an engine is "free revved" with a WOT blip, a large percentage of the engine torque is accelerating rotating masses in the engine - the reaction causing the chassis to roll. When driving - especially in higher gears, the engine is accelerating much more slowly and (hopefully) the majority of the engine torque is being reacted by the output shaft, leaving only a negligible portion to roll the chassis.

[Kelpiecross]

Unfortunately this is one of those examples of Smokus Pocus. When an engine is "free revved" with a WOT blip, a large percentage of the engine torque is accelerating rotating masses in the engine - the reaction causing the chassis to roll. When driving - especially in higher gears, the engine is accelerating much more slowly and (hopefully) the majority of the engine torque is being reacted by the output shaft, leaving only a negligible portion to roll the chassis.

I would think that as long as an engine is producing torque whether accelerating, driving at a steady speed etc. the engine will twist in the opposite direction and transmit this twisting torque to the chassis through the engine mounts.

I have heard that some speedway sprintcars are reverse rotation.

[gruntguru]

What you say is true, but apart from the inertial torque, an equal and opposite torque is applied to the final drive housing. If the car has independent suspension, the final drive housing will transfer this torque directly back into the chassis, canceling most of the torque applied to the engine mounts.

If the car has a live axle the drive torque will be transferred to the ground as a "jacking" couple and/or directly into the chassis via the axle linkages. Careful design of the linkage arrangement can cancel or even reverse the jacking effect.

[Lee Nicolle]

Reverse rotation engines were common place in Sprintcars about 15 years ago. I don't think anyone uses them now. But it was the same theory that Smokey was using.
And a sprintcar engine with 6-1 gearing has a **** load of torque reaction.

Edited by Lee Nicolle, 29 July 2013 - 09:52.

[gruntguru]

Sprintcars have a live axle, so reversing the rotation of a sprintcar engine reverses the torque applied to the rear axle housing. This will transfer "weight" from the inside rear tyre to the outside rear when power is applied. A normal CCW engine does the opposite.

This is a much more significant factor than reversing the small inertial reaction of the accelerating engine, especially one with no flywheel and therefore very low rotational inertia.

Edited by gruntguru, 30 July 2013 - 00:50.

[Kelpiecross]

It is not uncommon to see drag racing cars lift one front wheel off the ground due to the engine torque reaction (assisted by weight transfer due to acceleration).

[Magoo]

Reverse rotation engines were common place in Sprintcars about 15 years ago. I don't think anyone uses them now. But it was the same theory that Smokey was using.
And a sprintcar engine with 6-1 gearing has a **** load of torque reaction.

I think it's one of those recurring fads in auto racing through the years. Seems to capture peoples' imaginations for some reason.