Thanks for opening this thread.
So far the r1 motors are proving to be awesome. The first sample 13.5 motor tested, which was picked at random, tested better than the best ORCA, team Powers, REEDY, TP, killshot ever tested by us. We know that the top of the production should be as close to a d3.5 as it gets.
In a Sedan, the R1 13.5 gave us a hot lap 0.2 tenths faster than the d3.5. Two whole tenths!!!!
What. I can tell you is the motor build and quality is as good if not better than what is available currently out there. The motors have more RPM than the d3.5, so much so, that when unloaded you can hear it rev up in the car. A LOT!
In a 13.5 sedan i am gearing 2 teeth lower than with a D3.5, the motor still has more top speed (it is visibly faster) and has a lot more midrange. It runs more like a mod motor Than a stock, always having power available when the peak is high on the battery. I actually dialed a little negative expo on the throttle to mellow out the throttle input an make it easier to drive because it just has so much rip.
When it comes to a 21.5 I would start 2 teeth lower with the timing mark at 25 (the motors have about 30 degrees built in). The motor should rev more, so it should give you the top speed you want. Temp and go from there. Don't be scared of gearing down even more to find the sweet spot, because these motors LOVE to rev.