What size engine starts to vibrate to much?

[lt1bird]

Looking to build a new engine. Im wondering what size engine is the max before vibration gets excessive. Looking to put the engine in a rz350 street bike chassis so I would like the engine to run smooth. Just wondering at what size and stroke it would be a little too much

 

looking for 80-90 hp on pump gas....not drag porting

[2004LEBanshee]

Im not really sure what is considered too much. I think bigger strokes make more vibration but could be wrong. I would use the stock RZ motor but if your set on something else maybe a Cheetah with PV's. You could get those numbers easy with a smaller one and maybe 4mm long rod.

[lt1bird]

Ya, need a whole new engine...... I was thinking of a 421 but seems like the 10mm engine would cost the same. crank prices etc... just wondering if the 10mm would vibrate a factor X more...... looking to use the cub heads..... maybe some 10mm guys could chime in....