Extreme bore stroke ratio
Extreme bore stroke ratio
(OP)
I build and race small (150cc) 4 stroke roadrace motorcycles. The new engine I'm building has a bore of 75mm and a stroke of 35.5mm and is a water cooled 4 valve. Has anyone had any practical experience, as apposed to theoretical, on anything like this?
My 2 valve air cooled twin 150cc is making 27Hp at the wheel,thats 172 hp/litre and has reached the limit of development. I've got to get better than 30Hp to beat the dastedly 2 stroke 80cc watercooleds.
My 2 valve air cooled twin 150cc is making 27Hp at the wheel,thats 172 hp/litre and has reached the limit of development. I've got to get better than 30Hp to beat the dastedly 2 stroke 80cc watercooleds.





RE: Extreme bore stroke ratio
There are many tuners/racers in that forum with practical tips.
RE: Extreme bore stroke ratio
Sorry this doesn`t help you out at all but was just intrigued if you`ve found any obvious pitfalls and good advise as a response to your thread....
Many thanks.
RE: Extreme bore stroke ratio
RE: Extreme bore stroke ratio
RE: Extreme bore stroke ratio
Haven't progressed any further yet but will update IF it ever runs.
RE: Extreme bore stroke ratio
I knew the b/s ratio was tame compared to a multi, never gave dukes a thought...still a bit concerned that mines a single, think ill have to just build it up and find out i guess??
thephantom, good luck with the project, dont let the MANY frustrations and mind crunchingly annoying steps beat you down with development!
RE: Extreme bore stroke ratio
The motor runs real good and make quite good power from 6000rpm - 14500rpm
RE: Extreme bore stroke ratio
RE: Extreme bore stroke ratio
Many thanks.
RE: Extreme bore stroke ratio
This got the piston back to the correct deck height. I removed 1 link from the cam chain, skimmed the cylinder head as much as I could without the valve hitting the piston.
Fitted a 2mm smaller carb and away I went. This was stage 1.
Stage 2 I remapped the ignition curve.
Power output on a dyno jet chassis dyno at the wheel is 33+ HP. I used the 250 exhaust system. I'm yet to optimise
the exhaust system for the 200cc motor. The compression is still a little low. I need to work on this area some more.
I hope this info will help.