Mc45D......was it real!!

[Frank Payne]

Have you guys seen many of the 30s with the 40 exhaust port? I know its factory because it is narrower than my other 30 with the 3 port exhaust set up. I've never seen anything in print about an updated cylinder but it is in fact marked with an MC30 stamp and there are no overstrikes on the stamping. If any one is interested, I'll send some snaps of both engines.

[lynn haddock]

GEM made manifolds with a fin to block off the third port.

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.YES they did, several models in fact
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[Tom Smith]

Frank, the only 30s I've seen are the 2 I have, both have the early triple port. The single port was the way to go. I've got a Koing that has hugh single ex ports. They have a small ring deflector in the top center of the port which prevents the ring from snagging the port wall. Something you could do with a Mac single port, it's probably 2.5 times larger than an Mc-40 ex port!

Koing ex port 1 .JPG

(812.59 KiB) Not downloaded yet

[lynn haddock]

The single exhaust port scheme has proven to be the superior design for maximum performance, in particular when coupled with an extra pair of smaller auxiliary ports --- the standard rule of thumb for the maximum chord width on the main port is 1/5 of the circumference -- most engines are supplied in a more conservative size than this so as to minimize the ring hanging possibilities.
Tom, the pictured Konig design (center roof rib) was used for a short time but for the most part was abandoned in favor of an arched roof design which proved to be more effective (for the safety of the ring)(and for best performance). Most of the current Italian and Japanese offerings are like this.