Author Topic: Thoughts on different transfer port bottom edge heights?  (Read 1604 times)

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Offline John Orchard

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Thoughts on different transfer port bottom edge heights?
« on: November 02, 2022, 10:45:41 PM »
I have noticed in a couple of cylinders (RM125M & DT1MX) that some of the transfer port outlets, being both the middle port of a 5 or 6 transfer design, has the bottom of the port open below that of the piston crown at BDC.

Does anyone know the technical reason for this, or your own suspicion? At first, I consider a little extra cooling for the piston, but why only that part? Then I consider; as the piston approaches BDC, the flow out of that centre transfer would abruptly change, or be different in relation to the other transfer openings possible creating a 'vertical wall' at the window, or directing the flow from that port in an upwards direction? Possibly creating a better wall of mixture (when combined with the transfers) to push out the exhaust gases?

I like to keep you Guy's entertained, and me learning (just to take it to the grave).
Johnny O - Tahition_Red factory rider.

Offline pokey

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Re: Thoughts on different transfer port bottom edge heights?
« Reply #1 on: November 06, 2022, 10:15:10 AM »
Port design  has changed since jennings and its  mostly about reducing turbulence and producing more torque in the usable range hence the staggering of ports. What happened 50 years ago isnt what has been found to be better today.

Offline John Orchard

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Re: Thoughts on different transfer port bottom edge heights?
« Reply #2 on: November 06, 2022, 11:28:42 AM »
Port design  has changed since jennings and its  mostly about reducing turbulence and producing more torque in the usable range hence the staggering of ports. What happened 50 years ago isnt what has been found to be better today.


Yes I noticed that change in porting styles over the years, are you saying that you think that design was the old-school way of incorporating some turbulence? I guess the change works as the idea was left in the 70's, takes me 50 years to dig it up again ha ha ;-)
Johnny O - Tahition_Red factory rider.