RZ/RD 350 & Misc. 2-Stroke Tech BBS

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PostPosted: Tue Sep 04, 2018 12:35 am 
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hey guys,
I've seen it mentioned here before when I used to come on years ago but I can't find it now,
what are the more ideal cylinders to use for a stroker engine? im about to go pick up a motor and the guy im buying one off has a few sitting around, so if I have a choice which would be the more ideal for putting a 4mm stroker crank in? 31k or 1ua?


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PostPosted: Tue Sep 04, 2018 11:29 pm 
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I was advised by Martin at Mad Biker Designs in the UK. who did my head and cylinder work on my 385 to go for the 31k version as the porting was better suited to use with the +4mm crank. He is very helpfull and would be able to explain in much greater detail I'm sure. There a few guys on the rd crazy forum in the UK who have gone this route before also.
Good luck with the build.
Paul


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PostPosted: Wed Sep 05, 2018 9:30 am 
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really you should re-grind if you're using a standard cylinder...

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PostPosted: Fri Sep 07, 2018 8:46 am 
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nokturnal, I will be getting them worked when I get them, but I do remember seeing somewhere on here mentioning that 1 is better than the other for use with a stroker crank... so I guess im asking which is the better base to start with if im getting a stroker crank?


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PostPosted: Fri Sep 07, 2018 11:55 am 
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people have used them with a spacer plate and stock porting... maybe that's where the recommendation comes from. I believ the only difference between years is a slight difference in porting, which would likely be a non-issue if you are reporting.

maybe not though... maybe someone has info I am missing.

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PostPosted: Fri Sep 07, 2018 12:16 pm 
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The 31k barrel/head combination is the preferred pick.

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PostPosted: Fri Sep 07, 2018 1:52 pm 
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why

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PostPosted: Fri Sep 07, 2018 8:50 pm 
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My 1UA's are happy a +4 and +2.

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PostPosted: Fri Sep 07, 2018 8:51 pm 
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nokturnal wrote:
people have used them with a spacer plate and stock porting... maybe that's where the recommendation comes from. I believ the only difference between years is a slight difference in porting, which would likely be a non-issue if you are reporting.

maybe not though... maybe someone has info I am missing.


Ive ridden a bike with a spacer plate on 31k cyls and it had a very linear power delivery and we (Aaron and I) felt it was dull to ride, he later fitted different pistons and removed the plate, it was a different bike. My view is that a spacer plate is not the way to go. To be honest very few (any?) on this (and other) forum ever use them if you search.

I do agree that I doubt you'd notice the difference in the porting on the cyls with a 'bum-dyno'.

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PostPosted: Fri Sep 07, 2018 10:33 pm 
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JonW wrote:
nokturnal wrote:
people have used them with a spacer plate and stock porting... maybe that's where the recommendation comes from. I believ the only difference between years is a slight difference in porting, which would likely be a non-issue if you are reporting.

maybe not though... maybe someone has info I am missing.


Ive ridden a bike with a spacer plate on 31k cyls and it had a very linear power delivery and we (Aaron and I) felt it was dull to ride, he later fitted different pistons and removed the plate, it was a different bike. My view is that a spacer plate is not the way to go. To be honest very few (any?) on this (and other) forum ever use them if you search.

I do agree that I doubt you'd notice the difference in the porting on the cyls with a 'bum-dyno'.


Just saying that’s where the recommendation MAY have come from. I have no idea.

I’m not sure many people use stock ported cylinders with a stroker crank either... 31k, 48H, or 1UA flavor

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PostPosted: Sat Sep 08, 2018 7:02 am 
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Using a +4 crank and a 2mm spacer at the base gasket nukes your exhaust timing to some 206 deg (think this was with a 31K cylinder).
The transfers also go up to (I think) some 134 which is waaaay too much.

And that's the reason why getting rid of the spacer and machining the head to accommodate 2mm more piston stroke is helpful.
The difference between 1UA and 31K is that the 1UA has 1mm higher exhaust and transfer ports. Depending on your other mods (like which pipes you have) and the desired application the "optimal" solution will vary.
In a nutshell: The 31K's would tend to give more rideability (=midrange torque) whereas the 1UA usually result in more top end.
In any case a simulation of the intended combination helps to pre-optimise everything.

If you have 31K and want 1UA: Simply get a 1mm spacer and machine the head just for 1mm more stroke - mission accomplished.

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PostPosted: Sat Sep 08, 2018 8:16 am 
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thing is, porting on a stock cylinder is not "optimal" when EVERYTHING is stock, not sure why anyone would throw a new stroker crank at an engine without having the engine ported/machined properly. seems like a waste.

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PostPosted: Sat Sep 08, 2018 5:36 pm 
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PostPosted: Fri Sep 14, 2018 8:57 am 
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nokturnal wrote:

Just saying that’s where the recommendation MAY have come from. I have no idea.


That would have been that Dumb ass Roger

31k are best EX port will sit at 196/197* and your be able to change the transfer roof angles with out going to high on the timing!!!!


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PostPosted: Thu Sep 27, 2018 11:39 pm 
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nokturnal wrote:
why


I was going to say, 31k is Glyn's preference for port timing and head rework, although he can make either work with a recut dome. But Glyn responded.

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