TOPIC:

As some may know I started restoring a Porsche 936 and ended up with restoring a CS chassis for the Porsche 936 and Countach body. I'm having some problems with choosing the right motor and gears. The goal is to build an unique authentic runner with the best parts from that time.

Motors choices:
- RS-540SD Black Motor
- RS 540SD Black Motor Endurance
- Sport Tuned

Gear choices:
- default pinion gear that came with the Porsche
- 21T pinion that came with the Sport Tuned motor
- 18T or 20T gears (50175)

For which combination should I go? I can't seem to find much information about which combo's are good, I don't want to strip my gears offcourse. Based on the sticky "List of Cars / Motor Pinions" I should go for a 540SD with the 18T? The sticky contains a lot of information but doesn't include the 58008 as far as I could see.

I'd go with the Sport Tuned. The other motors are very cool but I'd keep them in good shape since they are a lot rarer.
Besides that, the Sport Tuned probably is the better motor (when it comes to efficiency) anyway.

Tried some calculations but that didn't amount to a definite result.
I conclude though that it would be best to start with the smallest pinion and see how hot the motor gets from that point on.
Possibly the range of 14-16T (like on a Group C with a Sport Tuned and the same wheel size and a spur size that's close)...
So that would be the stock 58005 pinion (15T I think).

Thank you for the advice. I'll go for the stock pinion and will monitor the motor temperature during a run.

ps. just out of curiosity, will a motor quickly become in a bad shape when using them? I mean they don't suffer a lot if the temperature is right?

It's not that they become in bad shape generally, there's just no way to replace the brushes (they're not rebuildable).
You should be able to do dozens of runs before that will be a problem though...