What? Only a dozen?

I knew a guy about 25 years ago that had a performance Jet ski business. As one of his services he offered porting. He must have done hundreds and I never seen any that really cooked except for one he finally hit upon. As luck would happen, the costumer seized the engine so he got it back and I got a chance to have a peek at it too. Even thou he had a perfect example in front of him, he still couldn't emulate the performance on other engines he ported. (this guy was dangerous with a porting grinder in his hands) I took measurements and noted port angles and directions, realizing less is more. When I got home, one of my engines was pulled from the hull and ported like the one I had seen. It was much stronger but not quite as strong as that miracle motor.

On one of my 55AX's, I radiused the inlet notch in the crankshaft (no change in timing) and radiused the bottom edge of the transfer ports on the outside of the sleeve. The bar that the metering tube fits into in the carb was air foiled(thinned) as well. The engine was started and blew plugs right away, I tried a cooler plug, better but it still wasn't happy. I went to FAI fuel and #8 plug, BINGO! A bit more power and rpm as as it had on 15% but now with no nitro, it did have to idle a little higher tho. This engine was flown like this for about 1 year till it went in from servo failure. I needed to take it apart to get the mud out. At this time I raised the exhaust port with two small notches, one to either side of the ring guard/web. This cuts into the nickle plate so it's a peel risk, even if you do everything right. The engine now could be ran on 15% and gained 1000 rpm over stock when ran on the same performance muffler.

As you can see, a very, very subtle port change can have huge effects, and if you don't know why you are cutting metal here or there you will be making junk.