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A new 60cc cylinder from Spookytooth Cycles fits right onto the cases of a 48cc Grubee engine and has the same bolt spacing for the intake and exhaust that the 48cc has. Here's its specs: .9mm deck, 137.2° exhaust duration, 102.5° transfer duration, 17.4° blowdown, 115.5° intake duration.
It is a bolt on modification but I recommend you at least do these 2 thing to it: 1) use an exacto knife to trim the included base gasket to perfectly match the base of the transfer ports since it sticks into their flow area. 2) smooth the transfer port roofs which have a nasty lip which would disrupt flow at peak rpm. Just use a rotary tool with a grinding disc.
Here's the specs on my test engine that I upgraded to 60cc: 14mm Dellorto carb with .58mm main jet, PIRATE CYCLES intake, standard exhaust pipe with two small holes drilled into the end for less flow restriction, no head gasket, Jaguar CDI installed. The cranking pressure was 100psi and the top speed was 28.8mph (46.3km/hr) at 6530rpm.
I lathed 3mm off the head mating surface and installed the .7mm head gasket. This resulted in 120psi cranking pressure and 32.4mph (7340rpm) which was a 9.4% gain with better power throughout the rpm range. It was lathed till there was only .5mm "rise" in the mating surface.
Unfortunately I ordered two sets of cylinder/head/piston and they didn't pack them well and the bottom skirts of both cylinders were slightly bent, enough to not let the piston slide past. I had to bang on them, bend them, and then use the dremel on them to make them usable. So don't order two sets. I like the fact that the heads center the spark plug which gives better power than using a slant plug mount head. I personally would rather just lathe the standard head instead of buy a high compression head. None of the numb-skulls that sell heads ever tell what the new compression in psi will be once they're installed.
I was going to also test the new 60cc cylinder/head/piston with my Rock Solid reed valve that I had bought for my 55cc cylinder, but the hole spacing don't match since the 55cc has wider spacing than the 48cc and 60cc. The 55cc is also a bolt-on and may be preferred for high performance because the Rock Solid reed valve for it is wider, offering more flow area which is critical at top rpm. Since my crankcase is completely stuffed I should buy the Arrow reed valve to put on this cylinder since it has much more flow area than the Rock Solid. (Since it sets back from the intake it increases crankcase area and will make high rpm power suffer unless you stuff the crank.)
It is a bolt on modification but I recommend you at least do these 2 thing to it: 1) use an exacto knife to trim the included base gasket to perfectly match the base of the transfer ports since it sticks into their flow area. 2) smooth the transfer port roofs which have a nasty lip which would disrupt flow at peak rpm. Just use a rotary tool with a grinding disc.
Here's the specs on my test engine that I upgraded to 60cc: 14mm Dellorto carb with .58mm main jet, PIRATE CYCLES intake, standard exhaust pipe with two small holes drilled into the end for less flow restriction, no head gasket, Jaguar CDI installed. The cranking pressure was 100psi and the top speed was 28.8mph (46.3km/hr) at 6530rpm.
I lathed 3mm off the head mating surface and installed the .7mm head gasket. This resulted in 120psi cranking pressure and 32.4mph (7340rpm) which was a 9.4% gain with better power throughout the rpm range. It was lathed till there was only .5mm "rise" in the mating surface.
Unfortunately I ordered two sets of cylinder/head/piston and they didn't pack them well and the bottom skirts of both cylinders were slightly bent, enough to not let the piston slide past. I had to bang on them, bend them, and then use the dremel on them to make them usable. So don't order two sets. I like the fact that the heads center the spark plug which gives better power than using a slant plug mount head. I personally would rather just lathe the standard head instead of buy a high compression head. None of the numb-skulls that sell heads ever tell what the new compression in psi will be once they're installed.
I was going to also test the new 60cc cylinder/head/piston with my Rock Solid reed valve that I had bought for my 55cc cylinder, but the hole spacing don't match since the 55cc has wider spacing than the 48cc and 60cc. The 55cc is also a bolt-on and may be preferred for high performance because the Rock Solid reed valve for it is wider, offering more flow area which is critical at top rpm. Since my crankcase is completely stuffed I should buy the Arrow reed valve to put on this cylinder since it has much more flow area than the Rock Solid. (Since it sets back from the intake it increases crankcase area and will make high rpm power suffer unless you stuff the crank.)
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