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Post by islandscrub on Oct 17, 2017 13:30:31 GMT -5
??
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Post by islandscrub on Oct 17, 2017 14:43:00 GMT -5
I see, so why not use those all the time? Is there a drawback to using a mini?
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Post by 90GTVert on Oct 17, 2017 15:26:19 GMT -5
Is there a drawback to using a mini? Less displacement. Longer strokers and bigger bores make larger displacement (more cc). |
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Post by islandscrub on Oct 17, 2017 15:45:12 GMT -5
Less than you could have, but more than stock?
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Post by AtariGuy on Oct 17, 2017 16:34:36 GMT -5
Pretty much. The idea is that you won't have to do much (if any) machining to your cases but still get something more than you had. Its like taking out your 39.2mm stock stroke crank and replacing it with a ruima stuffer at 41.4mm, you gain 2.2mm more stroke with next to no machining on your case. On a stock bore, you gain 2.8cc displacement, a 5.7% increase.
That, vs a 44-46mm stroker. It's guaranteed you'll have to open up the 50cc mina cases and machine them to fit the larger diameter crank. Some cases may not even have enough sidewall left after machining to seal around the largest strokes
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Post by 90GTVert on Oct 17, 2017 18:28:47 GMT -5
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Post by jdl357 on Oct 17, 2017 18:46:13 GMT -5
So could I cut my cases, put in a 54mm bore bbk and leave the stock stroke crank in to get around a 90cc engine?
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Post by islandscrub on Oct 17, 2017 19:22:47 GMT -5
Looks like it, according to the chart, but who knows what other issues you'd run into.
Thanks for all the answers, I was just curious as to what this all meant!
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Post by moofus02 on Oct 17, 2017 19:27:48 GMT -5
So could I cut my cases, put in a 54mm bore bbk and leave the stock stroke crank in to get around a 90cc engine? The cylinders are set up for the stroke. You change the stroke to much and port timings get all crazy strange. Mhr77 was 39.2 stroke and 50mm bore. Ryan ran one he sold me then he built another brand with the same set up. Spaz ran the mhr77 in his Zuma also |
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Post by spaz12 on Oct 17, 2017 22:45:45 GMT -5
A male midget? Just sayin.
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Post by islandscrub on Oct 17, 2017 23:04:53 GMT -5
A male midget? Just sayin. Just look at him go! |
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Post by jdl357 on Oct 18, 2017 10:04:55 GMT -5
Could you guys point me in the right direction of big bore kits I can use with still having a stock length stroke crankshaft? Looking for around 90cc or so. Thanks guys.
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Post by 90GTVert on Oct 18, 2017 10:39:56 GMT -5
I don't know if you'll get much closer to 90 than the 77cc stuff on a stock stroke : scootertuning.ca/en/search?controller=search&orderby=position&orderway=desc&search_query=77cc&submit_search=Otherwise you're stuck with stuff around 46-48mm bore. You could use them with a 41.4mm stroke (or Autotech355 is sselling a 41.2) to get around 70-75cc. Durations will increase a little and you may need to spend a little extra time on setup. Autotech355 on eBay used to sell 42mm cranks that were said to fit in the stock cases, but now I'm not seeing those and seeing his new 42mm cranks labeled as actually 41.2mm makes me wonder if the old ones were 42mm or not. I guess you could try a 41.4mm stroker crank and a short 54mm cylinder (90cc stuff often comes in short or tall cylinders, with short being for shorter strokes and tall being for longer strokes). Being only 0.6mm off of a 42mm stroke that is stock on many 90s, it may work with some effort. That could get you around 95cc. Personally, I'd just cut the cases and build a 103cc (45mm stroke and 54mm bore) if I wanted a "90". You're gonna have to pull it all apart and cut the cases to fit the big bore cylinder anyway. Might as well cut it for the crank and do some trenching if you go that far. Either that, or if all you want is to be fast... lots of 70cc setups will smoke the typical 90. |
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Post by 190mech on Oct 18, 2017 13:07:23 GMT -5
Another problem with fitting a 90cc jug to a 50cc crank is rod length,90 crank has 85mm and 50 is 80,so that would be very difficult to overcome..I agree with Brent,just go all 90,,nice used cylinders and cranks can be had for cheap if you search 90cc quad parts on ebay..I recently got a nice 52mm cylinder and piston/rings for $21 shipped!
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