Compression vs horsepower

[Stone]

It's time to act on all the input you guys gave me and make some improvements. I am going to buy a new driven clutch because mine is worn out.....I expect this to provide a significant increase. In case it doesn't, I am prepared to rebuild the top half of the motor; if I go this route I also plan to bore it 25mm over.

I have 105 PSI cold and I understand that if I rebuild I will get something like 120-125 PSI.

Does anyone know how compression and cylinder volume effect horsepower?

[EZ GO L4 Beach]

Should make more power. More room for a bigger explosion.

[mike_dmt]

Do you mean 25cc over?

What does it test out at when its hot?

[LVCJ]

In short, increasing the cylinder volume (by increasing the bore), will increase the combustion chamber volume. This in effect does 2 things. First, this increases the compression ratio and second, it increases overall engine displacement. In turn, this results in higher power output.

This becomes quite complex mathematically, but I suspect that the said change will be little, perhaps unnoticeable in this "small" motor in by itself.

Adding such things as cams, greater fuel/air mixture, timing, etc. would enhance the use of a larger combustion chamber and therefore enhance power.

[clr.R4tch3t]

Is this a 2 stroke or a 4 stroke? Your sig shows what I believe is a 2 stroke.. you can bore those up to .50mm over with a factory style piston. Anything over that would be custom. You can also bump compression by shaving the jug and head. There are a lot of things you can do to bump the performance of your motor.

[Spicyunicorn]

Beings compression is 105 and you expect 125 I'm going to assume this is a two stroke that being said on my single cylinder 215 CC stock two stroke Yamaha I bored it over 1.0 mm or roughly 4 thousands over witch on a v8 would be noticeable but don't expect any performance gain on a single cylinder two stroke... It takes fuel to make power and after a rebuild with largest oversized piston you don't have to rejet the carb to keep it from leaning out so if it doesn't require more fuel you won't make more power

[Shepard]

If you bored your cylinder to the max number -- the output horse would not be noticeable. What you would experience is the feel of a new engine. It wouldn't require rejetting the carburetor.
Here is the easiest example to explain -- in Nascar they all run the same size engine, 358 cibic inch small block GM I believe. It starts its life as a 350 and is bored to the max of .080. A bore job of .080 increases the displacement 1 inch per cylinder times 8 equals a 358 cubic inch engine. When you start with a cylinder of 43.75 cubic inches -- adding 1 cubic inch more doesn't really do much.
So boring out your small engine -- to the max is only going to be a fresh engine in output.