I want to buy a slant head for my supposed 61cc engine, thats what the sticker said, I thought I was buying a 49cc. Does anyone know the actual bore size differences? I measured the bore on the 61 and the bore on my other engine, a 49cc slant head from bgf, and they measure the same! The supposed 61 is more powerful (5mph faster with a larger sproket!) so I do think that maybe the diplacement's are correct and the difference is in the stroke (as ridinrich told me) but I have not checked that yet. Both engines have 6mm head studs. Can anyone direct me to the real bore and stroke specs for these engines? Or as i have read, are there no real set specs and they differ from one manufacturer to the next? I dont know which head to try for this engine, one for a 66 or one for a 49. If i remeber correctly they both measured at 40mm on the bore. I'm going to see about doing some port matching tomorrow so I'll get the real #'s for the engines I have.