how big can you go

DIRTY DOG

DIRTY DOG

XS650 Guru
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ok had a discoussion with a guy on F/B how big can you go with stock xs650 cyl's I have built xs650 for over 30 years and 706cc was as big as I was ever told I could go I went bigger one time and didn't last but a few runs am I wrong I'm here in the US so are stock juggs diff over sea's ??
 
DD,
750 kits are available (and they can be punched some more...), but it's the bottom-end and the lower cases that are your limiting factors. I've heard (someplace :umm:) that 75ish hp is about all they can stand, before going "BOOM! cough, cough, cough..." :yikes:
 
On standard liners 78mm is about as big as you can realistically go which equates to 706cc, I have come across a couple of 79mm bored barrels but the liners are very thin and fragile,
But if the question is how big can you go there are several mx outfits that have been taken out to about 1000cc by boring and stroking , just depends how deep your pockets are, with European rods you can bore to 880cc Heiden used to sell pistons or sp370 pistons will take it to 840,
 
I have done many 706cc and done 750cc but if you wanted to go bigger and I think the overseas 533 motor can go bigger but you would have to bore the cases and clearance the crank for larger pistons. In the past I have taken pistons from different bikes and used them in other bikes and I built a offset crank for a CB750 honda that put that close to 1000cc but it was a drag motor so lasting is not priority . I have also done some Suzuki motors that were 1100cc to 1500cc but tissue paper for case walls.
 
… years ago I attend'd a 650 Society event in Peoria.... National TT's.... one fellow had a XS 650 Special with a 950 kit... the " 650 " badge on the points covers...had the 6 cut off and reattached as a 9..... the only visual difference on the engine was the half inch plate under the cylinders…. he wouldn't say what it cost to have built.... he did say... he like'd " messing with Harley's " on the freeway.
I've done a few 750 kits... no problems.. but if go'n bigger or a performance cam.. I'd recommend get'n the cranks weld'd...
 

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