Author Topic: So what is the story with lowering transfer ports?  (Read 474 times)

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Offline John Orchard

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So what is the story with lowering transfer ports?
« on: April 19, 2019, 09:25:12 PM »
I have recently seen some two-stroke cylinders, and read some tech documents that show lowering the bottom edge of the cylinder transfer ports, below the top edge of the piston crown at BDC, some up to 6mm lower!!!

l'm guessing the only benefit to this is more exposure to a cooling flow from the air/fuel coming up the transfers, and/or maybe a more upward blast as the piston gets towards BDC?

Can anyone offer me some ideas here? :-)
Johnny O - Tahition_Red factory rider.

Offline TT5 Matt

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Re: So what is the story with lowering transfer ports?
« Reply #1 on: April 20, 2019, 03:21:58 PM »
I might be wrong but that would cause a lot of turbalance when going across the piston crown as transfer ducts are angled up to the combustion chamber to rid the c/chamber down of exhaust gas and charge the cylinder full of fresh air/fuel mix,sure you might drop a tad of piston crown temp but at a cost.maybe Lozza can chime in since he's more of a 2t specialist.

Offline djr

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Re: So what is the story with lowering transfer ports?
« Reply #2 on: April 20, 2019, 06:54:53 PM »
could you post up  the tech documents you mention ?
would be interesting to read.
 In theory I cant see any benefit from doing this, but maybe someone has discovered something new

Offline pokey

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Re: So what is the story with lowering transfer ports?
« Reply #3 on: April 20, 2019, 09:07:00 PM »
Lowering the transfers on its own does nothing as the effective size remains the same. If the piston was bevelled then the effective size /duration is changed. Id rather widen the port and repin the piston  if required and not play with the duration compression and head angles. The more you change the duration the more your existing pipe wont work.

Offline John Orchard

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Re: So what is the story with lowering transfer ports?
« Reply #4 on: April 21, 2019, 09:43:58 AM »
could you post up  the tech documents you mention ?
would be interesting to read.
 In theory I cant see any benefit from doing this, but maybe someone has discovered something new


lt is a genuine Yamaha document from 1972, l'll message you for your email address and will take send through pics.
Johnny O - Tahition_Red factory rider.

Offline John Orchard

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Re: So what is the story with lowering transfer ports?
« Reply #5 on: April 21, 2019, 12:22:16 PM »
could you post up  the tech documents you mention ?
would be interesting to read.
 In theory I cant see any benefit from doing this, but maybe someone has discovered something new


The Yam tech pages were just loaded on the DT2MX Facebook page if you are following.
Johnny O - Tahition_Red factory rider.

Offline OverTheHill

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Re: So what is the story with lowering transfer ports?
« Reply #6 on: April 22, 2019, 09:37:48 AM »
https://www.ebay.com.au/itm/1970-Yamaha-DT1-CMX-Cylinder-amp-Head-DT1-GYT-Piston-Port-Vintage-Racing-Parts-VMX-/352128162739?hash=item51fc795bb3&nma=true&si=0UA7WZMExJTENgEAPqBmfMGFnqM%253D&orig_cvip=true&nordt=true&rt=nc&_trksid=p2047675.l2557
Check out this cylinder & pics [if link works] as you can see the rear transfer is lower at the bottom than the other one. no idea why but have seen that on my go fast cylinders off various models. I'm sure my chrome gyt dt1 cylinder was like that but i don't have that cylinder any more.

Offline John Orchard

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Offline sleepy

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Re: So what is the story with lowering transfer ports?
« Reply #8 on: April 22, 2019, 03:44:58 PM »
I have recently seen some two-stroke cylinders, and read some tech documents that show lowering the bottom edge of the cylinder transfer ports, below the top edge of the piston crown at BDC, some up to 6mm lower!!!

l'm guessing the only benefit to this is more exposure to a cooling flow from the air/fuel coming up the transfers, and/or maybe a more upward blast as the piston gets towards BDC?

Can anyone offer me some ideas here? :-)

Perhaps it is to maintain the turbulence in transfer flow caused by the piston edge all the way through the transfer duration.
Tech document from 1972, not exactly current research. I have a book here from 1963 on Improving two stroke performance. I'm sure it was cutting edge at the time but laughable now.

Offline Lozza

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Re: So what is the story with lowering transfer ports?
« Reply #9 on: April 22, 2019, 10:11:35 PM »
I have recently seen some two-stroke cylinders, and read some tech documents that show lowering the bottom edge of the cylinder transfer ports, below the top edge of the piston crown at BDC, some up to 6mm lower!!!

l'm guessing the only benefit to this is more exposure to a cooling flow from the air/fuel coming up the transfers, and/or maybe a more upward blast as the piston gets towards BDC?

Can anyone offer me some ideas here? :-)

I wouldn't be copying that.  Some tid bits from the documents still hold true . Piston crown is the hottest and the more slowly exiting cool intake charge that contacts the piston crown the better. With a single exhaust port the intake charge sitting in transfers is not going to start moving until BDC when the lowest pressure is in the exhaust . Be interesting to look at the next few years to see what changed
Jesus only loves two strokes