Pistons for 9 Port Macs?

[steveohara]

Rick,

Your experience is consistent with my comments on this board previously.... the third port or "piston port" induction setup on the early Macs when used in tandem with a reed valve is only useful for ease of starting and to help generate a smoother idle. At wide open throttle in the racing rpm range that system serves no useful purpose and can allow some loss of intake charge as the piston starts down the bore. Working from TDC the reeds will close and trap the charge but the "piston port" passage remains open until the piston travels back down far enough to close it off. By blocking the passage with a simple gasket the incoming charge is uneffected as it will flow through the reeds but the potential loss back out through the third port passage it prevented. Of course, once you block that path it doesn't matter what type of piston is used since there is no flow either way in the third port passage and there are no boost ports to feed via the piston.
Filling in the passage that is already blocked off to prevent flow is a logical improvement... gain some stuffing but no effect on flow. I thought the Jr. Mc49 classes were always a spec class... how did you get away with modifying the engines in that class?
Steve O'Hara

[Gary Wlodarsky]

Just my two cents worth...been on here for a couple of years and this has been the most informative discussion yet....thanks to all you guys for some great info...

Gary

[Rick Chapman]

Steve,
The rules said you could use any gasket and I used the gasket to block off the passage..
The Plug, well that's another story... LOL
We went through many tech's and never was disqualified..
Rick