When I ordered my pulleys, the company sent out 30mm wide ones. Most guys with similar engines to mine in the US Mustang Drag Racing scene are using 50mm or wider belts. I'm using Gates HTD belts. About 30% stronger are Gates Powergrip belts. Then the big momma of belt technology - the Gates GT2 Polychain. These belts require only 20% of an HTD belt for the same torque rating - BUT they are a lot more expensive, and the belt pitch isn't quite the same. Both belts have an 8mm pitch, but the physical shape of the tooth is defferent. While the tech guy said that it should work well, he didn't rule out the fact that the belt might not even make it to 6500rpm without also failing. The difference in tooth shape, combined with both belts having the same recommended belt speed might make the Polychain go the same way as the HTDs.
Anyway, if I know that I'll break stuff over 6,000rpm, then I have a pretty good reason not to go over that. I think my valvetrain and rotating assembly will thank me for that!
So, how many Pommy Cobra nuts have you persuaded to come to DVSF3?