Is there such a thing as an 80cc 2 stroke?

[william42]

For those that never learned geometry in school...

No, there is no such thing as an 80 Cubic Centimeter 2-stroke engine in the bike engine context.

Engine Cubic Centimeters (cc) DISPLACEMENT is measured in a cylinder by geometry math.
The Volume of displacement is measured by the Bore width in centimeters of the cylinder * the Stoke length in Centimeters the piston can travel, period.

The simple volume that can be displaced with the pistons movement in the cylinder.

The head is where all the 66 Cubic Centimeters of compressed air/fuel mixture is shoved into and ignited.
The smaller that area, the higher compression ratio and usually, the bigger the bang (power) you get.

Most 66's are like 8:1 compression, that puts the heads CC size ~8.25cc give or take how your measure it, but regardless of size, the head IS NOT part of an engines displacement number.
That is the Compression Ratio and what matters when the 2 numbers are combined.

And just because something can displace more fuel mix does not make it stronger or better... All that is decided in the head by compression and spark timing and measured in any numbers of ways like Horsepower or Kilowatts.

Heck, a 48cc sent up right with an expansion chamber and such will run with a stock 66.

That's what really irritates me about the marketing BS specs and try to get others not to go along with it.

So what is the actual Engine Cubic Centimeters of a 49cc china motor, or 66cc

 

[MotorBicycleRacing]

So what is the actual Engine Cubic Centimeters of a 49cc china motor, or 66cc

48cc is correct as they aren't 49cc
40mm piston x 38 mm stroke = about 48 cc

47mm piston x 38 mm stroke = 65.?? cc
47mm piston x 40 mm stroke = 69.?? cc

 

[KCvale]

So what is the actual Engine Cubic Centimeters of a 49cc china motor, or 66cc

There are 48cc 2-stroke engines, 49cc 4-stroke engines, 66cc 2-stroke engines and one maker of a 70cc engine.

There in no such thing as an 80cc engine, 2-stroke or 4-stroke, they are 66cc.

 

[gary55]

Pi x R square X stroke. There are a lot of variations.

 

[KCvale]

Pi x R square X stroke. There are a lot of variations.

Cylinder Width x Stroke Length.

 

[gary55]

Cylinder Width x Stroke Length.

Just curious if your pistons are square, cause you have explained how to get the volume of a cube.

 

[gary55]

if I remember right a slant head is 7cc, meaning it'll be either 73cc or 76cc depending on whether it's 38 or 40mm stroke. the straight plug head on a 40mm stroke might be 80cc

in any case, my theory is that the "80cc" thing came about as a misinterpretation of what the markings on an FM80 rod meant.

Slant head is 6cc, straight plug is 10cc. So 40mm stroke, and straight plug head gets real close to 80cc in volume which don't mean s**t cause were displacement people baby. We don't change our engine size cause we put a new head on.

 

[gary55]

For those that never learned geometry in school...



Engine Cubic Centimeters (cc) DISPLACEMENT is measured in a cylinder by geometry math.
The Volume of displacement is measured by the Bore width in centimeters of the cylinder * the Stoke length in Centimeters the piston can travel, period.


Wrong
..

Most 66's are like 8:1 compression, that puts the heads CC size ~8.25cc give or take how your measure it, but regardless of size, the head IS NOT part of an engines displacement number.
That is the Compression Ratio and what matters when the 2 numbers are combined.

Wrong again


That's what really irritates me about the marketing BS specs and try to get others not to go along with it.

Another thing that is irritating is when people don't even attempt to get the facts right before professing their knowledge of them.

 

[crassius]

pi x r square x stroke

 

[gary55]

pi x r square x stroke

An dat's da way da cookie crumbles, or in dis case da Pi multiplies.