We offer a complete trackside tuning service at all the major racing events we attend, as well as our fully blueprinted line of motors we sell as well.
With this being said, I agree with Butter. Trackside, everyones hands are tied to what they can do to handouts. It's most important to start with a high quality brush, have it totally blueprinted and dyno tuned, and then be given the proper rollout/gearing.
There are several motor tuners that we sell our brushes to OEM that can perform just as thorough of a trackside tune-up to your motor at a race that we could...comm cutting, break in, rebuilding, gearing, etc; They have started with quality components, and are up to speed on our latest products and tuning techniques.
If results matter to you in deciding, (and they should,) do some research to see who and what has been/ is winning in the application in which you are racing.
Also do some research to see what additional products and services are offered from the companies you are purchasing from. Few offer proprietary brush compounds, balancing etc; which is fine, just be certain you educate yourself in what is being done to your motors and what products are being used. This way, repeatability will be easier to achieve at rebuild time.
Good Luck, and feel free to contact us any time to answer any additional questions you may have.
"Where The Fast guys Shop"
Putnam Propulsion Competition Motors and Accessories