48cc to 60cc upgrade by cylinder swap

Discussion in 'Performance Mods' started by jaguar, Nov 3, 2012.

  1. jaguar

    jaguar Well-Known Member

    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.)

    Attached Files:

    Last edited by a moderator: Dec 18, 2015

  2. Fabian

    Fabian Well-Known Member

    Maybe you should experiment with Fred's new medium compression twin spark plug cylinder head and soon to be released high compression twin spark plug cylinder head to see which combination works best for various cylinder port specifications with the 66cc engine.
  3. jaguar

    jaguar Well-Known Member

    As you know from the other thread I am no fan of twin spark plugs for small cylinders since the flame front has so little distance to travel from center to side. What I am suggesting here is a very simple method of upgrading to a larger engine with little to no complications.
  4. BigBlue

    BigBlue Active Member

    As always, Its a pleasure to read your articles.

    Thanks for posting,

    AKA: BigBlue
  5. Fabian

    Fabian Well-Known Member

    To heck with the flame front; it makes no d.am.n difference with either type of cylinder head - twin spark plug cylinder heads "look" so much nicer
  6. Fabian

    Fabian Well-Known Member

    Think of a single spark plug cylinder head as Khloe Kardashian (not your first choice, or your second choice, or even your third choice if you have to look at her, and given other options, but she's still a Kardashian, and a logical conduit to being in company of her prettier sister) and a twin spark plug cylinder head as Kim Kardashian; the kind of presentation that you prefer to look at and ride!!!
  7. jaguar

    jaguar Well-Known Member

    with intake extension +2mph and more grunt

    I just added the offset intake manifold from JNMotors which is about 4" long, added a 2+1/2" long rubber automotive hose connected to a 3/4" diameter (19mm) short section of copper tubing (to insert into the carb clamp) and gained 2mph (35.3mph top). And the grunt was as much as anyone needs without a shift kit or expansion chamber. Hardly even need to pedal taking off from a stop. really good power all through. I expected a low rpm power gain with a top speed loss but instead gained both low end and top end!
    I will add a picture...
    I guess I should add that the porting was slightly changed in stages but without any great power or speed changes as a result. Click on my signature link and go to the 60cc upgrade page to read the details. What made the greatest difference was increasing compression and adding the intake extension.
    Last edited: Nov 5, 2012