racerdx6

I have a really nice caliper, but it's only in MM so when I measure my stock motor comm's I can't really tell how close to smoking a motor is from having too small of a comm. So if someone could tell me what they think is the smallest safe comm size in a motor I would greatly appreciate it. I've heard .27" is just about the smallest safe size. Does anyone know what .27" is in MM? Thats the main thing I wanna know, thanks a lot in advance .

racerdx6

Oh, by the way, the motor I was measuring today was 7.3 mm . Now I realize how big of a comm a 9 mm comm really is , its huge!

dtm

.27 is 6.858mm that is pretty close to the limit. The performance of the motor usually drops a fair bit when you get to 7.0mm. I usually find 7.2-7.3mm is when the motor is running best...this is on a std size comm of course!

JDM_DOHC_SiR

iTrader: (31)

I`m with DTM on this one too...but I find that the sweet spoots on most of my 23T stocks are around 7.1 ish the motor is at it`s prime here..tons of RPM ...and power..

-Dave

StephenSobottka

iTrader: (8)

if u need to cinvert mm to in.

mm/25.4=in
inX25.4=mm

racerdx6

Thanks for the help guys!

Randy Caster

iTrader: (47)

Is this based on an Epic motor?

dtm

Not really just Epic.....I find this with pretty much all std size comm motors I have run...Corally, Maxtec, Yokomo, Top and Epic cans. As you get smaller you start losing too much torque and the RPM goes up. You can compensate a little by running more silver in the brushes....but then the comm wears out even quicker!

Randy Caster

iTrader: (47)

I'll propably just true down the comms in my epic revenge of the monster motors to the sweet spot and run silver brushes. Just trying to get the most speed I can out of the motors...

dtm

Haha...that is a very "expensive" way of obtaining power!

MaverickRacing

.292 is the optimum comm size, IMO. Ive had comms down to .267 before they came apart....


As far as cutting the monster stocks way down......Smaller comm = more RPM at the expense of torque. Bigger comms are the exact opposite. Since RPM x Torque = Horsepower, Id leave the comm how it is, grab some Putnam Green brushes, and opt for a slightly lighter spring.

StephenSobottka

iTrader: (8)

I like the comms big too, I like the torque they provide naturally this way, so i just use a lighter spring to get the rpm I want.