I have a GTB and 13.5 Orion brushless setup in my B4.

I wanted a bit more speed out of it, so I ordered a Hobbywing Xerun ( sensored ) 8.5T motor. ( got it cheap too, $45 shipped brand new off Ebay )

I also had my eye on a SpeedGem 8.5T motor, but the KV rating was much higher.

The Xerun is 4000KV, my orion I run now is 3200 KV, is this going to be a big difference?( I increased the timing on it, now it is much faster, kinda wish I had'nt bought the new motor )

I race at a track that has a long front and back straight, hence why I wanted a slightly faster motor.

You should definitely notice a 25% increase in power! The 8.5 will have more RPM's and power at the top end, where the 13.5 should have a low-end torque advantage. I'd drop a pinion tooth to compensate.

Thanks for the reply.

Right now I run the Stock Spur (87) and a 24 pinion and after even 10-12 mins, it is still cool to the touch. ( I mean, around 95 deg when i temp check it )

So I would need to go down to a 23 maybe even a 22.

My concern is that it will run my battery out faster, I can run really long times with my current setup, and I don't really bash, so as long as it lasts 10-12 mins I am fine with that.

I run 2 turnigy 5000 mah 20-30c 2s lipos and 1 Flightmax 4000 mah 25c 2s Lipo.

Do I have the right C rating for a higher RPM motor?

Those batteries should work with an 8.5 , you might want to go even smaller than a 22 on the pinion though. Just temp it and see.

It will run out packs faster, maybe a minute or two less than your 13.5. Have run an 8.5 in a stadium truck on 4000's on a huge track and just made 10 minutes with it - it was down to 25%. The 5000 pack should have no problem.

I wouldn't go too far down on the gearing, it seems like [in general] undergearing heats up the speedo, overgearing heats the motor

Thanks again...

Yeah that is really my main concern right now. Our back straight away is around 100 feet, just to give you a idea of the size.

Last night, I ran my Turnigy trying to hit the cutoff, to see how long it will run, after 30 mins ( on the dot ) I brought it in and took a look. I was concerned the cut-off had been disabled, it was not, and when i threw it on the charger it was at 7.6v.

I feel much better about making the length in the mains now.

Thanks for all the input guys.