400 rpm

[stevieturbo]

A couple of points of clarification.

It’s the trials car that has no idle control not the donor car.

To further explain the need for the very low rpm.
The car could very well be being driven as suggested here at a 1000 rpm. This would most likely be on a very slippery surface. If traction is lost then forward momentum of the car is lost. To regain traction the rpm must be dropped so that wheel speed matches vehicle speed so that the attempt to regain traction is as gentle as possible. It’s in these circumstances that the very low rpm are required.

It sounds like low rpm isnt required, different gearing is required.

[rjwooll]

I guess the point of very low rpm is to limit torque in very slippery conditions. Using gearing to deliver low wheel revs with higher engine rpm would make it difficult to control.

[stevieturbo]

I guess the point of very low rpm is to limit torque in very slippery conditions. Using gearing to deliver low wheel revs with higher engine rpm would make it difficult to control.

It would make it an absolute doddle to control. You've full control over timing which will give a huge ability to manipulate torque, both reducing it quickly, and increasing it, with far less risk of stall.

[katana]

And don't forget there is a clutch for torque feed ! Any engine should run most efficiently in 'steady state' conditions ie constant load and rpm - what happens after that should determine drive. If in my example above 55 wheel rpm was too high (hard to think it could be - less than one rotation a second) the addition of a) a hi / lo range transfer box, like fitted to Landies ie 2:1 could halve wheel speed to 27 rpm! and b) fit an LSD so torque is shifted to the wheel with traction!

[stevieturbo]

And don't forget there is a clutch for torque feed ! Any engine should run most efficiently in 'steady state' conditions ie constant load and rpm - what happens after that should determine drive. If in my example above 55 wheel rpm was too high (hard to think it could be - less than one rotation a second) the addition of a) a hi / lo range transfer box, like fitted to Landies ie 2:1 could halve wheel speed to 27 rpm! and b) fit an LSD so torque is shifted to the wheel with traction!

I think a lot of these vehicles run open diffs ? and use independent braking on each wheel to shift drive around ? I'm sure I've seen videos of that or something years ago

Dont forget, most LSD's do not shift drive to the driven wheel as such, they just reduce the slippy wheels ability to slip out of control.

And a Torsen type diff would probably be useless for this type of application.

But with a brake to apply to each wheel you can reduce wheelspin and force drive to that other wheel. Albeit it requires drive input to do so ( unless you could automate it somehow )