S90 engine upgrades

YellowBeetleSB

YellowBeetleSB

Member
Does anyone make big bore kits to bring the s90 up to 125 or 150cc, similar to how TB sells big bore kits for the CT? I'm looking to get a little more power out of the s90 engine and I know lifans and aftermarket motors don't bolt up like they do on a CT.

thanks for your help.
 
dr atv has a piston that punches them out to 104cc. that's about the best you're gonna do for non-custom parts. There's a much bigger market for the upgrade CT70 stuff because the platform is similar to the CRF50/70. almost identical actually.

To get the s90 bigger you'd have to source a crank and or cylinder that has more bore and stroke. They also make a cam with more umph on the top end. i haven't seen anything that bumps compression up or displacement, significantly.
 
Enginedoctor said:
dr atv has a piston that punches them out to 104cc. that's about the best you're gonna do for non-custom parts. There's a much bigger market for the upgrade CT70 stuff because the platform is similar to the CRF50/70. almost identical actually.

To get the s90 bigger you'd have to source a crank and or cylinder that has more bore and stroke. They also make a cam with more umph on the top end. i haven't seen anything that bumps compression up or displacement, significantly.
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Hi from Kelowna BC I have a 1969 Honda S 90 i have owned for 50 years and would like rebuild the motor can you please direct me where to get the parts to punch it out to 104 CC as you suggest. Is there a higher compression piston nothing extreme just a fun riding bike with a little more HP. Norman
 
Hello and welcome, Norman. You have found a very old post and doubt enginedoctor visits here anymore. 2019 last seen on date.. If you are in Canada, you have Phatmx there and may be able to help.
 
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