Originally Posted by TJMac

You shouldn't have any problems.

They rate them according to how much juice they can handle. A 160amp ESC can handle more power than a 90amp ESC. That doesn't mean the 90amp ESC isn't any good, it just means you can't run crazy low turn motors. I run a Race in my daughters SC10 in 17.5 blinky and the ESC is so under stressed its ridiculous. She's run 15-20 minutes at a time practicing and the Race comes off the track @ 110-115F without a fan. You should have no issues running an 8.5. My only concern would be to check temps after 6-7 minutes if you decide not to run the fan (or can't .... B4 is a little tight).