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Post by scooter on Oct 12, 2014 23:00:44 GMT -5
If your scoot is a 150 it has 13/40 gearing. If your scoot is a 50 it has 15/51 gearing. Thank you Alley. |
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Post by scooter on Oct 12, 2014 22:50:08 GMT -5
Yeah wiki is always right  lol These numbers are tossed around allot on various sources. What I do know is for a fact other members here have reported a compression test reading of 150-160 PSI.. Does anyone know the calculation involved in converting PSI to 8-1 or 10-1 compression? In the end it doesn't really matter...What matters is what kind of compression am I going to get once everything is done. I'm not supporting or defending wikipedia but I have used their sources for research papers and they generally have quality information based on quality source materials. I'd probably believe a Haynes manual over a scooter sales website but I tend to check several sources anyway when I need to be sure, so I'll definitely be looking out for more sources to find out which one is more accurate. As for the psi thing, I'd trust actual measurements like that over either source, but I suppose that could differ from engine to engine and manufacturer to manufacturer. But yeah, if there's a way to actually measure it, that's better than taking someone's word for it in my opinion. Physically you can fill the head with water and measure how much water it held, and you could do the same for the cylinder but the math for a cylinder is really easy, so if you have the parts in hand, you can calculate what your compression ratio will be that way. |
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Post by scooter on Oct 12, 2014 22:35:16 GMT -5
That's from wikipedia, xyshannen. en.wikipedia.org/wiki/GY6_engineThey also list compression for two other gy6 engine sizes. They put their sources, such as Haynes Manuals, at the bottom of the article if you want to see how they got their numbers. How do you use psi to determine compression ratio? Is that like 150psi / 15psi = 10, where 15psi is normal air pressure? |
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Post by scooter on Oct 12, 2014 14:47:42 GMT -5
I would like to be able to calculate projected speed based on variator belt height, rear end gearing, and tire size. I'd appreciate info on gy6 gearing so I won't have to take my scooter apart to find out.  |
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Post by scooter on Oct 12, 2014 14:34:57 GMT -5
Bow down foo, you're in the presence of gy6 royalty! JK Ally, couldn't resist.  |
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Post by scooter on Oct 12, 2014 14:01:45 GMT -5
Wrong bro no mistake, cut a hair off at a time on a lathe tested after each cut. I am a genius at this stuff you are still in the learning stage. The prove of your ability and knowledge was just posted "overfilled your oil reservoir in a GY6", SAY WHAT  Alleyoop Okay, Boss. You win. |
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Post by scooter on Oct 12, 2014 12:15:42 GMT -5
In this pic you can see I'm wide open. i1287.photobucket.com/albums/a624/xyshannen1/beach_zps75715cbb.jpgI don't ride in the rain and if I did I'm still not worried. I "might" get a little slipping, but these things turn so fast any moisture will quickly be evaporated off. I only worry about torrential downpours and deep puddles. All of which are easily avoided. And my body work on this scoot keeps your legs at a safe distance. That red bell housing looks super with your paint job. I am afraid to run without the cvt cover on for fear of cracking my swing arm or cvt case or whatever that section is called between the engine and the rear hub. We just got through the rainy season as you know. I drive in the rain. One day I hit a deep puddle and water went up over the floor boards. I heard the airbox gurgle water. I had water in my drain tube. The water immersed my CDI and didn't even phase it, but I moved it up higher on the frame just to be safe. Your scooter looks good. |
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Post by scooter on Oct 12, 2014 12:09:35 GMT -5
But having said all that...now with the mods I'm currently doing, I know I'm going to have to play with my roller weights vs contra spring to get my engine in it's new torque curve of 6-8k RPMs. But I don't foresee ever having to mess with the bos length to get my desired result. I don't bother with a CVT cover and have extensively watched my belt on the variator and it goes all the way up to the edge of the variator. In fact I fear that if it ever goes any higher it will pop off. Yesterday, just by shear luck, I managed to put together enough individual parts to achieve a small reduction in the width of my variator, and the results were excellent. My belt rides closer to the edge and my RPM curve is much better. I have taken a special interest in variators and I can tell you that changing the boss length really is effective. There is nothing a contra spring or roller weight can do to adjust belt height. It can only go so high or so low given the dimensions of the rollers, back plates, variator sheaves, and boss length. Once you have enough weight to make it open all the way, no amount of weight is going to make it open any more. Yours is fine, but IF you needed the belt to come down, shimming the boss would be the way to go. But it would be a very small shim, not 1/8", not 1/16", but more like 1/256" - 1/64" or .004 - .015". It would be very easy for someone to overshoot that if they didn't do the math first, and I find a lot of people don't do the math. They'd rather work by trial and error, and that's okay, but can be costly and inefficient. From the picture he posted, I'd say he went too far, and from what he said of the results he got, I'd say he went too far. Alley is a smart guy, and experienced, and very generous, and helpful to everyone on the site, but no one knows it all. |
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Post by scooter on Oct 12, 2014 11:14:48 GMT -5
Increased compression adds HP, 12-1 is just about has high a compression you can have and still use pump gas plus octane boost. I'm going to have to do some research and find out if that high a compression iis even possible on these little motors. There are questions that need to be answered like clearance issues with the piston and valves. Then I don't even know how well the crank will hold up to such a high compression. I'm assuming you have something like the 157QMJ? That on is said to have a compression ratio of 8.8:1. 12 would be a 36% increase in pressure? Yeah I'm betting the crank will take a beating. I'm no mechanic though so I wouldn't know. Engine Displacement Power Bore x Stroke Compression Ratio 139QMB 49.5 cc 2.  hp (2.20 kW) at 7,500 rpm 39 mm × 41.4 mm (1.54 in × 1.63 in) 10.5:1 152QMI 124.65 cc 6.8 hp (5.1 kW) at 7,000 rpm 52.4 mm × 57.8 mm (2.06 in × 2.28 in) 9.2:1 157QMJ 149.6 cc 8.6 hp (6.4 kW) at 7,000 rpm 57.4 mm × 57.8 mm (2.26 in × 2.28 in) 8.8:1 |
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Post by scooter on Oct 12, 2014 8:09:44 GMT -5
Thank you, Dahling. I think my scooter is getting jealous!  |
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Post by scooter on Oct 12, 2014 7:16:58 GMT -5
I will have to take it to a machinist I know to have the deck surface millled a couple thousandths of an inch because I want 12-1 compression. Setting your compression sounds pretty technical. Congrats on such a righteous mod! How did you decide on 12:1? What was the reasoning behind that number? |
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Post by scooter on Oct 12, 2014 6:43:54 GMT -5
You obviously cut too much off. Blaming the mod for your mistake is like saying you shouldn't waste your time using motor oil because you overfilled your oil reservoir in a GY6 and got poor results, or that tires are useless because you once tried putting 20" tires on your scooter and it didn't work out.
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Post by scooter on Oct 12, 2014 6:34:39 GMT -5
How many times does your clutch pulley turn for each revolution of the rear wheel? How did you calculate this?
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Post by scooter on Oct 12, 2014 5:58:20 GMT -5
What RPM do you prefer at wide open throttle while accelerating?
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Post by scooter on Oct 12, 2014 4:20:25 GMT -5
Thanks. I agree that he should have known better. Randomly hacking on the boss isn't going to improve performance. It sounds like he didn't put much thought into it.  |
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hp (2.20 kW) at 7,500 rpm 39 mm × 41.4 mm (1.54 in × 1.63 in) 10.5:1