are they 80cc

The 80cc designation is a marketing ploy used by the engine manufacturers and kit suppliers. They include the combustion chamber into the equation which isn't the correct way to calculate engine displacement. The cylinder bore and the piston stroke, multiplied by the number of cylinders is the only true way to determine displacement. When you buy a so called 80cc engine you are actually getting a 66cc.

Many engine kit suppliers use the 80cc number because it works well with search engines when people are looking for motorized bicycle kits. Be aware that there are a few sellers who will advertise their engines as "true 80cc". It just ain't so.

Tom
 
The High Council of Motorbike Building arrived at the conclusion that 80cc China girl motors are really 66cc. I have not put a caliper and dial indicator to these engines, myself. I don't think 14cc makes a difference you can feel.
 
W/B that is true, I repaired a friends bike with a stock 66cc that didn't seem any stronger than my 48cc that I've ported. So in this case 18cc didn't make a difference.
 
What I said was my ported 48 runs as good as a stock 66, meaning you can get a lot with a little work.
Dang I hope you heal quick!
 
My understanding from riding both sizes is there is very little difference.
What the 49cc lacks in raw power, it makes up for by revving longer. Gear it lower.
and what the 66cc lacks in top end, it makes up for in grunt. Gear it higher.
Either engine can be improved substantially with careful porting.
But in the end, for MY money:"There is no replacement for displacement"
Why build a turbo 4banger for $25k when the same money will get a blown big block?
Same labor pays off better on the bigger engine.
But then again, I have no problem with lying my a$$ off to authority figures....
"Why yes officer, it IS under 50cc and therefore legal according to state laws"
:)
 
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I agree that the bigger engine has more potential, with the 48s getting harder to find there will be more people building 66s.
 
It's just a matter of getting them balanced right, and building a decent pipe, one of my '66/68.5' cc motors happily does over 9000 RPM. Lacks a little low down with a 36t, but flies.
The other one I'm still playing with, starts to ping up there, but will still do 9.
But I admit if there not balanced right, they start losing bits to vibration if you try and over rev them, I've heard the 48's tend to run a lot smoother.
 
I have had the 49cc and then upgraded to the (80cc) 66cc engine both have been great . The 66cc does go up and over hills without the peddle assist my 49cc needed on the same hills . Oh and yes officer it is only a 49cc engine no tags or license needed here in TX . The local police here did have ride my motorized bicycle to the station where they went through all their law books trying to find something to get me for . They threw an orange safety vest at me said wear that and your helmet then followed me outside and watched while I put on a good show of doing a lot of peddling to get going . Haven't bothered me again LOL
 
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