..being involved with testing the 21.5 motor for OVAL racing...we were looking for a motor to use as a STOCK type speed motor with the higher voltage batteries (LIPO).
Since most OVAL racing has been using 4 cell batteries for several years now in order to have a B/L motor that would run similar speeds with higher voltage batteries..a NEW motor needed to be designed.
Too often NEW motors overlook the entry level or even the vets who just like a more controlled speed. (EVERYBODY Doesn't want to run at LIGHTNING FAST SPEEDS)
We were involved with the 17.5 motor and the 21.5. As far as the speeds of it...it's actually still TOO FAST for a direct replacement of the 4 cell 27t brushed motor class. (The 25.5 we were testing would have been better)..and a 23.5 would have probably been PERFECT) But, this motor is very easy to drive...it runs for EVER, doesn't get hot and is a lot of fun in a Pan Car.
I haven't had the chance to stick one in my Touring Cars yet, but we'll be doing some of that this winter...because we've got some NEWBIES who really want to run brushless..but DON'T want to be ballistic...
As far as a motor that compares to STOCK 27t Brushed speeds...when properly geared..the 17.5 is MUCH closer to STOCK than a 13.5 is. The 13.5 when geared right IS Faster in everything we've tested them in so far...compared to a brushed 27t motor.
NOTE: On a Road Course track - it doesn't show up that the 13.5 is that much faster in many cases...in part do to the nature of speeding up and slowing down I believe...
We only saw about a lap and a half difference between the old 19t motors and Stock with the SAME drivers...but the STOCK motored cars could drive a lot deeper into a corner..and didn't have the high speeds on the straights. I think the same would be true of the 13.5 vs the 17.5.