What to Call The Ports
Sometimes the different transfers are referred to incorrecly - most commonly the fifth ports. It's easy to see how the mistake is made.
The exhaust port is the exhaust port - whether there's one, two, three or more. Extra exhaust ports are not counted as such, though are usually referred to as auxiliary or finger ports.
The main transfer port pair - those closest to the exhaut ports are called the mains (though this thinking is changing the name remains the same).
The second set of transfer ports, sometimes called the secondary transfers are the fifth ports. They got the name because when they were added the cylinder then had five ports - one exhaust, two mains and then two more to make five.
The last port or port set - typically placed directly opposite the exhaust port - is (are) called the boost or bust (up) port(s).
More info below...
I refer to the transfer ports as follows - this is how SAE does it (pretty much):
Front two transfers - Mains
Rear two transfers - Fifth ports (Blame Yamaha) #1 is the exhaust, #2 and #3 are the mains. Then they added a second set behind the mains the 4th and fifth ports. Now they have three sets on some cylinders - I suppose we have to call them the seventh ports... It gets confusing.
Boost port - Bust port (Blame Yamaha but I forget why).
Single Exhaust - Obvious
Single Exhaust with extra ports at 3 and 9 oclock - Single with auxiliaries, or finger ports.
Bridged Exhaust - One port divided
Bridged Exhaust with extra ports at 3 and 9 oclock - bridged with auxiliaries, or finger ports.
Inlet with holes feeding bottom end - Boyesen ports.
Fifth ports cut with additional hole(s) from inlet - MacDizzy port.
Inlet ports cut through into crankcase to feed the fifth ports - Double duty MacDizzy ports.
Mistakes - experiments. :)
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