I have a CR80R that's plated, and I think my LT250R is as well. Ohh I get it, you only bore what you need to save having to replace a head, because 1mm over is not going to give me any noticeable power differences?

 

You only bore to clean up the cylinder to accept new rings and piston for a rebuild not for any PERFORMANCE gain. Just to bring the engine back to oem specs. Now with that said if you go say from a 250cc bore to a 330 big bore well yeah you are doing it for performance but just to freshen it up - no gain.

 

Ahh this makes so much sense now!

What do you think a KDX80 puts out in horsepower? Since the engine is on a drag tractor I will be put into class according to my engines HP.

 

It has been a while and this project is still waiting for me but recent V8 modifications have got me thinking...since there is not much jug wall thickness to play with but this is a valveless engine...why not stroke it if the walls are thick enough to retain the detonations?

Stroking it will make high RPMs more intense on the structural integrity of the engine and some of it's parts, which might affect top end power so playing with a carb spacer or milling the carb tunnel length down may compensate any loss of power in a particular rpm range due to stroking; curving the power-band range?

With my buddies at the machine shop I may be able to make this work, if I can start with a crank from something like a KDX/KX 100cc/125cc it might be taller (longer stroke). Once that is machined to fit in my bearings I have the option of machining a shorter connecting rod or trying to modify one from something like a KX65 to work. My other option is changing the piston compression height on the wrist pin and there is not much room there...but it would help drop the compression back down to normal at TDC then I'm not sure but the piston skirts may be able to be shortened to not exceed into the crankcase on the bottom stroke and I could weld some reinforcement into the bottom of the piston with aluminum stock. Both the shorter rod and higher wrist pin can be combined to achieve the same result of lowering the compression.

I assume the tuning wouldn't be hard since it uses reeds and a carb, with a squish test between the piston tdc & head I would give it a kick and see how it performs. Maybe the same as a 100-125cc engine with just a whole hell of a lot more money and time, it might sound way different, the myth goes stroking to the same displacement gives more torque then boring to the same which would result in more hp.

In the end I can't fit a larger block in this chassis and I have no room for a water cooling system.