Boring-out 650 Cylinders

[KillerGriller]

Just for curiosity sake...What would be a better bang-for-your-buck: Overbore the cylinders on an existing 650 or purchasing a decent 750/850 motor and doing a swap?

Cost/effort vs. HP gains?

I don't plan on doing it, but looked into it when I was rebuilding an RZ350 15yrs. ago

[Steve]

Since you have a 650E, that increases the odds a bit, but I don't think the 750 will fit in the 650 frame.

And don't even think of the 850 engine. All GS850s are shaft-driven, your frame simply is not set up for that.

.

[Chuck78]

This exact same question comes up every few years.. same answer, see above. bigger engines, and even more importantly, the exhaust pipe spacing will not fit the frame.

besides, the 650E has the most efficient combustion chamber, piston, and head design of any of the two valves per cylinder engines. It makes the same horsepower or actually one more than an 8 valve 750. Right now for $200 shipped from Japan, you can get the GS650 stock OEM style cast pistons in a budget aftermarket big bore kit for 740cc. So a stock 650 makes the same horsepower as a 750, what do you think a 740cc big bore 650 will make? Just don't put on too big of tires and do hard launches, that's a lot of power through a stock engine!