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Old 04-24-2014, 03:26 PM
Theon Theon is offline
Motorized Bicycle Elite Member
Join Date: Jan 2014
Location: FNQ Australia
Posts: 1,440
Default Re: Bought bottom end from Boy Go Fast, should I be worried?

If he wont tell you its stroke it will be a 38mm.
I can't agree sorry MAP, but the 40mm stroke in my opinion makes a noticeable difference to the torque.
It is only really 5% more, but 5% more displacement x 5% more stroke, so more than 5% increase in power.
but the main thing is you will likely find that to get the compression up on a 38mm stroke motor you will need to deck the barrel if you want to set the squish.
Hence the 38mm stroke motors come with a slant head to try and correct the compression.
If I was just building a low power cruiser, then 38mm is OK, but if you want to try and get what you can from your motor then every 5% helps.
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