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Post by weatherman49 on Jun 14, 2017 18:16:34 GMT -5
an old school trick to add more power to an engine was to increase compression ratio. this was done easy and for the most part cheap by shaving/milling the heads has any one done this and what were the results?
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Post by gsx600racer on Jun 14, 2017 18:25:06 GMT -5
Are you doing this on a 2 stroke engine or a 4 stroke engine ?
If its a 4 poke, you have to make sure there is enough clearance between the valves and piston after the head is shaved. Too much compression will lead to other problems like detonation and overheating.
If its a 2 stroke, you have to make sure the "squish" isn't too small. If it is, you will also have detonation and overheating issues
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Post by weatherman49 on Jun 14, 2017 18:39:21 GMT -5
four stroke 157
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Post by weatherman49 on Jun 14, 2017 18:42:50 GMT -5
i know about the mechanical parts and the issues just wondering if any one has done it on a scoot and the results have a scoot that was given to me gonna make a rat scoot because the plastic is trashed and just wanted to see what kind of people have done it? have never seen a post on any forum about it!
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Post by 90GTVert on Jun 14, 2017 21:28:19 GMT -5
I didn't mill the head, but I ran my 155cc with no base gasket, just sealant, to raise compression. With that and a domed piston, I had to cut new valve reliefs.
People used to talk about milling 0.010-0.015" off if GY6 heads pretty regularly with good results. As gsxr said, check it all prior to doing any cutting and see what you have room for. You can measure it all out and see where your compression will be and take down cam specs to figure out dynamic compression.
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Post by greggkinney on Jul 12, 2017 21:51:59 GMT -5
I didn't mill the head, but I ran my 155cc with no base gasket, just sealant, to raise compression. With that and a domed piston, I had to cut new valve reliefs. People used to talk about milling 0.010-0.015" off if GY6 heads pretty regularly with good results. As gsxr said, check it all prior to doing any cutting and see what you have room for. You can measure it all out and see where your compression will be and take down cam specs to figure out dynamic compression. how ate you getting gasket maker to be thinner than the little thin base gasket? or do you mean thinner than a gasket plus sealant? i use the gaskets with no sealant and am not sure i could use permatex and get it any thinner unless i just smeared a skin thick layer on and tightened it wet lol. i did put a qmb head on with no gasket or sealer, just a smidge of indian head and it worked great no longer than i used the 47mm bbk |
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Post by 90GTVert on Jul 14, 2017 15:08:38 GMT -5
how ate you getting gasket maker to be thinner than the little thin base gasket? not sure i could use permatex and get it any thinner unless i just smeared a skin thick layer on and tightened it wet There ya go, you answered this one for me.  |
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Post by jeff84 on Jul 14, 2017 16:08:44 GMT -5
this would also retard the timing just a hair, wouldn't it?
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Post by 90GTVert on Jul 14, 2017 16:21:47 GMT -5
I'd think the difference would be negligible, but I didn't check.
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Post by james82nd on Feb 15, 2018 18:32:50 GMT -5
scrappydogscooters.com sells a great 52mm bore kit with pop up piston that works great with their Taida racing head with larger valves and three angle valve seats.
the bore kit is made from HOCA not cheap Chinese made
the base bore gasket is .5mm thick uncompressed.
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Post by dexameth on Mar 13, 2018 10:55:52 GMT -5
scrappydogscooters.com sells a great 52mm bore kit with pop up piston that works great with their Taida racing head with larger valves and three angle valve seats. the bore kit is made from HOCA not cheap Chinese made the base bore gasket is .5mm thick uncompressed. Partsforscooters.com has some good kits, and FYI Hoca stuff and SSP-G is the same. Same quality, same foundry. Check it out. |
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Post by 3strokeengine on Mar 16, 2018 13:21:27 GMT -5
When you mill the head it does retard the cam timing a few degrees and thus lowers cranking compression. Im sure overall its still a net gain if you took .030-.040 thou off of it.
Personally if i want more compression i go to a bigger bore with the stock sized head. It keeps your cam timing the same and because the bore is larger than the head you get more quench in the combustion chamber which helps mix the fuel and air better and is more resistant to detonation.
Also the gy6 is a hemi head design so the flame front moves very slow towards the piston that combined with the stock 8.8:1 compression ratio is why these motors feel lazy stock. If you want it too feel a little snappier with a little work you can advance the ignition timming with a flywheel advance key(the so called "performance" CDIs are snakeoil but thats a whole other topic). 4 degrees advanced is fine just be sure to run 93 octane fuel and jet it a little on the rich side
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Post by 90GTVert on Mar 16, 2018 13:48:31 GMT -5
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Post by 3strokeengine on Mar 16, 2018 14:51:03 GMT -5
Thanks, your videos taught me a lot about scooters when I first started getting into them |
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Post by houseoffubar on Apr 19, 2020 16:06:23 GMT -5
this would also retard the timing just a hair, wouldn't it? Yes, leaning just slightly to more torque than too end, but again, slightly |
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