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Post by JonW on Nov 1, 2010 5:53:51 GMT 1
Was thinking about using some of the YPVS 250 parts i have in my spares haul as theyre just door stops right now and started to think I might fit a long stroke bottom end that way i can upgrade to a bigger top end later and get the benefits of the extra ccs without redoing the whole engine... hmm...
So, in my merry minds eye i wondered what I might get cc wise from such a beast... applying high school maths and a few quick tests to be sure of what i was doing, i get...
bore x stroke = cc's
64 x 54 = 345.6cc so close enough to 347cc of the RD350... cool
...but when i do the 250 version i get
54 x 54 = 291.6cc... er thats a 300 not a 250... but everywhere says the 250 has a bore of 54mm and we know the stroke is the same as its the same crank so im a bit confused...
Anyone know what im doing wrong?
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Post by JonW on Nov 1, 2010 5:59:51 GMT 1
Im being thick... there is more to the equation... I think the 350 just works out that way with a number close to what you think you need, but actually its wrong... thats only 1 cylinder...  |
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Post by JonW on Nov 1, 2010 6:02:00 GMT 1
The more i think and search the more i come to realise its still simple maths but you need a pi r squared part as well to work out a disk, thats the bore, then elongate that disk to get a stroke and x by 2 as there are two cyls... thick as two short pigs me... |
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Post by JonW on Nov 1, 2010 6:03:37 GMT 1
Ok... found this on wikipedia  They add: If the bore is 10 cm and the stroke is 5 cm with 4 cylinders, the calculation is: 3.1416/4 * 102 * 5 * 4 = 1570 cm3 ≈ 1.5 liters |
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Post by JonW on Nov 1, 2010 6:11:02 GMT 1
If the bore is 64mm and the stroke is 54mm with 2 cylinders, the calculation is:
3.1416/4 * (64x64) * 54 * 2 = nothing useful... hmm....
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Post by JonW on Nov 1, 2010 6:13:38 GMT 1
Ok, the maths having failed me I found a proper calulator online... phew! www.bgsoflex.com/displacement.html I can sleep easy now... My +4mm 250 will be 265cc... Sorry for answering my own question like some sort of numpty and for Gary not saying i was an idiot LOL |
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Post by Norbo on Nov 1, 2010 6:57:44 GMT 1
fitting a 4mm crank seems an expensive way to get a few extra cc
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Post by winnerevo1 on Nov 1, 2010 9:25:50 GMT 1
You almost got there without the online calculator!  To find the volume of a cylinder you have to calculate the area of a circle (area of the bore diameter) and multiply by the length (stroke length). Obviously that's for 1 cylinder.  |
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Post by JonW on Nov 1, 2010 12:48:54 GMT 1
Norbo, its not to get a few extra ccs on the 250 cyls... seems a strange thing to do, but its for a number of reasons; one is that im waiting for news on a couple of new big bore top ends coming in 2011 and want the bottom end ready (ie stroked) for those when they come to market instead of having to do a new crank etc, another is that i have the 250 kit sat on my bench all honed and ready to go with new pistons etc also all the electrics etc so its a cheap way to get the LC on the road whilst i sort out my rusty LC engine (the RZ engine belongs with my KTMaha project if im honest), another reason is that down here there is a 'super mot' when you put a vehicle back on the road if its been off the road a while, and for that im sure they will check the cyls for their cc stamped on the sides and if they do these will say both 'Yamaha' and the right numbers, even if the engine number itself isnt the same as the old one.
Life is never simple LOL
Thanks Winnerevo1, yep thats what i was thinking, but the online calc was much simpler LOL
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howie
L plate rider.
Posts: 30
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Post by howie on Nov 1, 2010 20:19:08 GMT 1
here we go. got this from my boy.
vol of cylinder= pi r squared times length.
so 3.142 x 27 x 27 x 54 =123687 gives the vol of one of them x2 for both
=247375 but this is in millimeters and there's a thousand of them in a cc.
so divide by 1000
=247.375 cc
think thats it. or have we all moved on from that now. am usually one step behind every body else. lol
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