Stein's Black 63 found

[Charlie A]

Originally Posted by Liteweight

Thyose painted stripes might be an old racers trick. Where the paint stops burning is where the max temp is.. This is where you'd cut the tube for best torque effiencency.

liteweight

Used to use a crayon to do that. Mark a line the length of the collector and where it melted away was supposed to be the proper length for the collector.
Don't know if it worked or not but that is where we cut 'em.
Ran better with than without.
Not quite as colorful as the two above!