A friend of mine builds motor cycle race motor and has a flow bench . We got to talking and i brought my mach motor (830cc) down to him I whanted to put new crankbearings it this summer .I'm glad i did found that the center of the crank was only 117deg from the pto (120 on pto117 on center120 on the mag)that would explain the vibration it had .Any way as we were talking i asked him if we could do some flow work on the cyclinders and some porting on the cases? so before we pulled the motor apart (the motor was complete carbs 37.8mm, reeds, plugs ect) we hooked up the vacuum to the exhaust flang Stock machz pipes.And let here rip WOW their is a big differene in all three cyclinders about 45 cfm(all holes were stock other than the sleeves for the big bore no other porting was done to the cases we used the stock reeds opened to .50 thats what he sets all his 2stroke motors at carbs at half throttle ) this was the base line with the position at bdc pto was 582cfm center was 627.5 mag was 597.35cfm this was done for 15second on each cyclinder . ;) He was vey surprised that it was that low he said his GP 280cc bike will pull 780cfm from a 40mm flat slid carb . my question is being that their both reed case motors is he right in the fact that with major porting it's possable to get around 825-870cfm per cyclinder or are they just two totaly different motors ?We all ready bored the carbs out to 39.4mill and that added 46cfm to the combo ;) when we pulled the head off and he look at the wash he sugested that we dimple the tops of the pistionsand head to get a more unified wash out toward the rings and away from the center of the pistion to help in ring seal ? I use dimpling on all of the race race motors that i build for oval racing along with pistion porting (we drill .030holes around the thrust side of the pistion all the way down to the top ring it lets gas get behind the ring to help in ring seal and adds 8-10horse.down side is u have to pull the motor down every 6-8 outings)Will it work on a two cycle(dimpling top of pistion and head I had the head of my banshee 420cc done and it made 80hp with out and 85with it ) will that work on a sled motor or not I,m not concerned about melting it down i have 3 extra sets of cyclinders ready to go I only have to pay for pistions and a 12 pack for labor for a resleeve and renik I,d like to get vforce reeds and a tepa flow witha 1mill base gasket I'm going to keep the 99mach z pipes i like then better than the crankshops pipes

I would like to see a pic of this dimpling on the piston head.

I used to have a few 1977 ZZ 340 & 440 ACat sleds that both engines had dimpling on the intake side of the piston.
There could be up to 20 dimples drilled into the material.

...I have no idea what this was used for and had spare brand new pistons that were dimpled as such.

how bout some pics of your peestons???

Joe, On earlier piston designs (prior to Trapez or dyke style rings) dimpling meant drilling tiny gas ports around the circumference of the piston crown to the rear of the ring land to positively pressurize the back of the top ring increasing the ring's sealing pressure on the cylinder wall. The downside was, these gas ports would quickly block up with carbon deposits using the oil technology available at the time.