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I have a question about motors , how much of a difference will there be between a 21,500 rpm - 350cm @12volt motor to 20,000 rpm - 300cm @12 volt motor? I race on a small ninco 2 lane layout (4'x16' and the longest straight is 14') and should I use 8/27 or 9/27? The motors in the cars now are 25,000 rpm motors and are way to much and make the cars not fun to drive at all! Thanks for any help!

What cars?

My guess is that you will enjoy the 20k motor more based on the fact you dislike the 25k. Like Harry said it does also depend on the car and also if you're running magnets or not.

Gear ratios aren't quite a black art

There are lots of guides out there but this one might help
http://www.hotslots132.com/understandin ... a-109.html

If you go 27/8 the 1:3.375 you are lowering the ratio and may see a slight increase in acceleration and decrease in top speed, but probably not a lot with a 20k or more motor on your small track.

27/9 or 3:1 is probably the most common ratio, on some tracks and some cars I go 27/10

can you turn the voltage down on the power supply this can also improve things - Ninco motors are rated at 14.8v and are lower in RPM on 12v

cheers
DM

The cars I am changing the motors in are Avant lmp's with no mags. Thanks for all the info it helps a ton!

Both those motors sound brutal!! You have to be racing with traction magnets? I cant see how you get get that sort of torque through the wheels without massive wheelspin otherwise. Probably 9/27 rather than 8/27. You say youre running 25k motor, but whats the torque of that motor, and what gear ratio?

So what dont you like about the current motor? Is it too punchy down low or too much top end that makes it unusable? Draw a graph. The graph will look like a "triangle". Torque on the y-axis and rpm on the x-axis Multiply the motor torque by the ratio. ie 9/27 = 3. So 300gcm x 3 = 900. So draw a straight line from 900gcm (y-axis) to divide the motor rpm by 3 (20000 / 3 = 6666) and draw 6666 on the (x-axis). Now do this for all the motors and gear ratios.

If you dont like the current motor because its too punchy down low them make sure your triangle is "less" at the torque end of the graph. If it has too much top end make sure your graph is less at the rpm end. If you dont like both, make sure your trianle is less (smaller) at both ends. Hope that makes sense.

I agree with Marty use Mark T' slower rpm motor they work great on shorter tracks. I didnt have to do anything but take the pinion off the old motor and put it on the new.
Marty :auto-checkeredflag:

Both of those motors have a lot of torque and may not be your best choice for non-magnet racing. You often can compensate for a high torque motor by changing the grar ratio, but I would expect that even geared at 2.5:1 that these motors would be a handfull. Motors with about 160gcm of torque seem to work best if you run without magnets. A lot of motors out there can put out a lot more than their rated RPMs. The humble Scalextric 18K motor can put out 23K or more if you get a good one.