Boost ports

[mcbob]

Might be a question for eith uncle Tom or uncle Steve

What difference in performance between the single boost port of the 101 and the twin boost ports of the 101B as i have fitted a boost port window and a gem boost port cover into a SP125C Chrome bore engine i found that trying to cut the 101b style port near impossible as the SP125C has a fixed head making access very awkward ?
Would the difference be that great ?

McBob.

[Pete Cioruch]

Macbob: If I am not mistaken the 101AA does have the 2 boost ports and the 101A may have also. I have a couple 101AA's and they both have them. Not sure about how much power gain they add.

[mcbob]

Sorry Pete to confuse you the early 101's has a removable window insert for the boost port but Mac changed that to the two finger boost ports so i just wondered what sort of difference was between the two types power wise.

McBob.

[steveohara]

Guys,

Only the first generation 101 had the single boost port with the removable window, all others that followed have two acorn shaped machined in from the top. The first generation 101 also had two exhaust ports rather than one as all of the later models have.
To answer Bob's question, I don't think you will find any difference in performance between the two vs one large port but the rings will last longer in the two port design. If you ever have the opportunity to run a first generation 101 long enough to see some wear you'll find that the rings do a number on the top edge of the single flat top boost port just as they do to the top of the large single exhaust ports in the A and later versions.
Steve O'Hara

[mcbob]

Sounds as if i'm barking up the right tree then ............ Thanks Steve