Article by Travis @ Buggy Depot
Background in Mechanical, Electronic, and Systems Engineering.
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A detailed explanation of engine displacement and the relationship of “bore x stroke” to the power production of your engine. Displacement calculator included at the bottom!
GY6 Engine Size Calculator
The displacement of your GY6 is
Note: 58.8mm is the largest size bore that can be installed on the GY6 engine without machine work to the crankcase halves.
So what is displacement?
The size of a piston-driven gasoline engine (like the GY6 in our buggies) is measured by displacement of it’s internal combustion chamber. The term displacement literally refers to the volume of space the combustion chamber “displaces”, and is usually measured in cubic centimeters (cc’s).
Displacement, there’s no replacement!
The reason displacement is so important in engine design is that in general there is a direct relation between the amount of displacement, and the amount of power ultimately produced by the engine. There are a lot of other factors, but as the old saying goes: “there’s no replacement for displacement!”
Just like when measuring the internal volume of any cylinder (like a can of Cola, which is 355cc by the way), displacement of an engine is determined by the bore size (diameter) and stroke length (depth). Bore size is simply a measure of the piston diameter. The stroke length is how far the piston itself travels inside of the cylinder. For example, the standard bore of a 150cc GY6 piston is 57.4 millimeters, and the piston travels 58 millimeters within the cylinder every cycle.
Bore x Stroke = Power!
The more displacement an engine has, the more air and fuel mixture it can suck in from the carburetor. The more gas and air you can confine into a space and ignite, the bigger the boom! This translates to more power at the wheels of your buggy. The internal volume of the engine can be upped by either increasing the bore or the stroke sizes. While these both do the same thing, they are not created equal. This leads us to the next point…
Why strokers are important
Stroked engines not only have a larger displacement than a stock engine, but there is also a greater amount of torque produced per additional CC when compared to only a bigger bore. This is because a stroker crank produces more leverage than a stock crank. Think of it like this, it is much easier to remove a stubborn rusty bolt with big wrench than with a small wrench, right? A bigger wrench will take that bolt off easier because your hand travels in a larger diameter circle, resulting in more torque being applied directly to that stubborn bolt. It’s all about leverage and the same principle applies to the crank shaft of your buggy. A longer stroke means that the piston (your hand) has an easier time turning the crankshaft (the wrench) and ultimately the rear tires (the bolt).
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