What speed can you get out of a 32mm engine?

Joined
Apr 9, 2018
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#1
I know the 40mm spacing cylinder is better but I was wondering what speed/hp you can get out of a 38mm stroke engine with 32mm stud spacing. Is 45-50mph achievable? Would mods like crankcase matching porting exhaust and decking get it to produce these speeds?
 


Joined
Mar 19, 2018
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#2
Yes, it would be possible, I have a 50cc that goes 40mph (All of which have 32mm stud spacing) so with the more displacement, it would definitely be possible. To get 40 MPH out of your bike, I haven't done anything crazy; HP carb, Jets, sanded cyl head, NGK spark plug, CDH66 exhaust, OZ carbon fiber reeds, 36T sprocket. So if you did a similar setup on a 66cc with 32mm spacing it is possible to get 45MPH out of it, and with mild porting and a bigger carb, you could get 50MPH out of it. The one problem with 32MM spacing is getting a nice reed valve on the engine. My dad and I made an adapter to put the 40mm reed on a 32mm engine and it works great.

To summarise, yes its possible to do with standard mods.

-Dan
 
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Apr 9, 2018
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#3
I ported the exhaust a little and smoothed it with some steel wool on a drill bit. I also took the base gasket and filed down where I marked with a sharpie to casematch. I’m putting Japanese bearings in it as well. Gonna be cool I’m building it for my neighbor as a present. I’m just experimenting as the fastest we’ve gotten an ht engine is maybe mid 30’s on a slight downhill. I remember his usual speed on the first engine was 25ish.
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FNTPuck

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Jul 2, 2018
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#5
When porting make sure you widen the ports but do not blindly raise or lower them since it will effect your port timing and while slightly raising it can give you more top end, going too far can ruin the jug. Also, for the exhaust there is no need to port larger than the exhaust flange so I trace that to a sheet of paper, cut it out, then sharpie mark the jug for a nice circle exhaust port which I then blend into the oval shape. inside the cylinder.

Be SUPER careful if you try to touch the transfers...I only recommend doing what you can reach from the bottom with a round tip bit, since it is super easy to ruin a cylinder if the bit jumps while trying to port the transfers from the top. I have done that already and ruined an otherwise well ported head :(.
 
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