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Post by nelson on Jan 10, 2014 18:20:24 GMT -5
isn't that compression ratio really low ? 5.8:1 ? I have never really paid much attention to compression ratios on a two stroke but I know for a four stroke and probably wouldn't even run a compression ratio like that
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Post by 90GTVert on Jan 10, 2014 20:27:08 GMT -5
That's the effective or corrected compression ratio, not what we're used to hearing. Instead of using the stroke of 42mm from BDC to TDC they use the effective stroke which is the distance from the top of the exhaust port to TDC. It's prob closer to 10:1 uncorrected, but you'd need more info to know.
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Post by shakerdriver on Jan 11, 2014 9:24:52 GMT -5
I've got a couple of those sitting on the shelf in my garage, nice little motors IMO.
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Post by nelson on Jan 12, 2014 11:23:45 GMT -5
Thanks, likely I will turn this one into a hot street engine. Maybe full on race, dunno yet. But its gonna be fun in my jog!
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Post by kevin55950 on Jan 13, 2014 0:11:52 GMT -5
Cast iron 100cc was my favourite street motor ever ! Keep a 70cc for a race build, you get good results for not that much. Over 70cc it's a lot of time and money involved to have good power.
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Post by 190mech on Jan 13, 2014 6:44:28 GMT -5
I agree with Kevin!The 90cc+ engines dont breathe as well as the smaller engines due to the smaller transfer area and poor reed design and sizing..Heck of a good street motor though!!  |
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Post by nelson on Jan 13, 2014 11:19:08 GMT -5
well before i do any work on the 90cc i will do some research. Doesnt the Hoca cylinder have extra transfer ports? It would seem there is more power to be had from more displacement. I understand what you guys are saying. I dont think i am really in a hurry to build it so time and money(within reason) isnt an issue. In the end i am sure if you are going to make a race only motor you would be better with more displacement to begin with? I agree with Kevin!The 90cc+ engines dont breathe as well as the smaller engines due to the smaller transfer area and poor reed design and sizing..Heck of a good street motor though!! |
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Post by moofus02 on Jan 13, 2014 11:28:30 GMT -5
As the bore gets bigger the transfers get smaller and the mina motors have a poor Reed design to start with. 2strokd picked up et when he went from 54mm to a 52mm Cylinder he ported I assume from the extra area in the transfers but him or 190mech could clarify that. The big motors do make good torque and Desent power good Street motors
Sent from my SPH-L720 using proboards
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Post by kevin55950 on Jan 13, 2014 12:33:06 GMT -5
70cc motors doesn't produce as much torque but you will have great HP to get good acceleration and top speed for race. 90cc will have plenty of torque to climb hills and carry stuff. But torque will kill cheaper/OEM gear box and CVT trust me  Broke so much clutches with the zuma, and gearbox cover bolts needed to be hardened or they were broken after a good acceleration, gearbox bearings needed to be changed for SKF because the oem ones were breaking often, primary gear shaft was always going too far in the gearbox (going out of the bearing) and broke me 2 torque drivers. Needed to loctite the shaft on the cover bearing and loctite the bearing in the cover to make it run without issues. Driving at 30mph, only giving a little gas from time to time was really nice. Can't have this feeling with a 70cc motor. |
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Post by moofus02 on Jan 13, 2014 12:48:17 GMT -5
The stock 90 gearbox should be stronger than the factory yamaha
Sent from my SPH-L720 using proboards
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Post by kevin55950 on Jan 13, 2014 12:53:21 GMT -5
I hope ! Zuma's gearbox is not that tough as I see.
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Post by moofus02 on Jan 13, 2014 13:20:47 GMT -5
I hope ! Zuma's gearbox is not that tough as I see. I've seen kits to put a support bearing in the cover at the clutch like the clones but I'm not sure how they mount the bearing or I would buy one for my Zuma Sent from my SPH-L720 using proboards |
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Post by kevin55950 on Jan 13, 2014 13:35:40 GMT -5
You have some kind of casting mark (riser) on the cover which matches on the primary shaft, if I remember you fit the bearing aligned to this point.
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Post by moofus02 on Jan 13, 2014 13:43:58 GMT -5
Yes I wasn't sure about that part. Looks like the kit has extension for clutch shaft that goes into the bearing but I didn't know how to locate the bearing and they leave that part out of the description lol. Why yamaha didn't put one in from the factory amazes me since the Chinese saw fit to do it
Sent from my SPH-L720 using proboards
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Post by nelson on Jan 20, 2014 15:41:34 GMT -5
My stock jog cases have the bearing in the cover with the extended shaft. Whats up with that?
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