49cc vs. 80cc

LR Jerry

Well-Known Member
Mar 14, 2011
i have the 49 c.c. slant head 2 stroke engine on a 20" frame with 20" wheels and a 44 tooth sprocket. My friend has the 80 c.c. 2 stroke engine on a 24" frame, with 20" wheels and a 44 tooth sprocket. His motor is broken in, and mine isn't fully broken in yet.
his gets going from a dead stop better than mine does (more c.c. = more bottom end torque) but i can catch him once we get going and stay side by side with him at 25-28 mph.
he does weigh more than i do (i am 155 lbs) but even if i ride his 80 c.c. bike, i still get about 25-28 mph top speed out of it.
i think the 20" wheels takes away from some of the top speed because most bikes with 24" or 26" wheels seem to get a little more top speed than what we're getting with the 20" wheels.
Seems you put very small wheels on very large frames. The way most bicycle frame sizes are measured is by the seat post length. However frame geometry can still be very different depending on model and manufacturur for the same size seat post tube. Still generally speaking a 24" inch frame would be for someone around 6'4"+.

Here's a frame proportions calculator that can let you know the general area you need in a bicycle frame size for your particular body build.

One would have a very difficult time keeping the crank from hitting the ground with a frame that large and wheels that small. Even with a 20" seat post tube would be for a person close to 6' tall. Probably still too large of a frame for 20" wheels and without having crank drag.

Now if you made a very common mistake of thinking wheel size is the same thing as frame size (these frames that use 20" & 24" wheels are generally a lot smaller); one could possibly put 20" wheels on a bike that had 24" wheels.

My desire here is simply to educate so that we're describing things with the correct technical terms.
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New Member
May 16, 2020
From reading posts most folks prefer the 80/66cc motors. Cheaper prices and way more choices on upgrade parts.
I think I'm leaning in that direction. They seem easier to come by in Canada. Thanks for responding. I like to hear every9ones opinion.


Well-Known Member
Sep 23, 2013
The 66cc generics, and 69cc (Grubbee Zeda PK etc) have 47mm bore and are compatible with the very large aftermarket cylinder heads. Fitting one of those will cool your engine enough to allow for any other mods and bolt-on upgrades you choose to add in the future.

The 69cc engines available in the USA and Canada (and I even got a Zeda 80 in UK) also have 40mm wide intake stud spacing which is compatible with the newer bigger reed valves that can be fun and effective.
The old 32mm intake spacing on the 49cc and 66cc engines is only compatible with the little RSE reed valve and its clones, which due to its small size is said to mainly reduce noise and reversion rather than boost torque.
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This past spring I took out my 49cc engine and put a 80cc on. I am wondering if there is any real difference in power/speed. I did initially note a bit more climbing power, but later that just died down and engine started conking out on very steep inclines.

I was hoping I'd get 30+ mph, but if I go beyond 20mph, engine rattles like crazy and nuts/bolts start falling out. So I can't really go faster.

Someone told me that 49 cc works better, he actually put my old 49cc on his bike and said it works great! He suggested I go back to 49cc.

What are other people's experience with this?