[Mach1Canuck]

Earl, like a few others have posted, try different sizes. Thats why I recomment starting with the smallest hole, and keep increasing size and retrying until you find the best benefit.
I would rather spend 5 min pulling out the plate and making the hole bigger as few times...rather than spend 1 hour, make it once, and it doesn't work the first time so you forget it and live with your hanging RPM's...