First time I've seen a YT on this topic, one that I have wondered about myself.Congrats at a great attempt! Great to see a science-based approach to this issue. I am an Electrical Engineer by training (with a chainsaw obsession!) so the math is not a problem for me, but I agree in a large part with your approach with measuring chamber volume . One point to note; When measuring compression values with a PSI gauge, the volume of the tube from the spark plug hole to the gauge is included. In effect, you are increasing the chamber volume by the amount of air in the tube connected from the spark plug hole to the gauge. That extra volume will tend to lower the values displayed by the gauge. Because air is a compressible fluid, and the volume of the pressure gauge connection is larger than in real-world conditions, (i.e. without a pressure gauge attached) so you get a guage value LOWER than the operating conditions . Also note that there will be a (dynamic) pressure differential from the spark plug hole to the gauge measuring point, again due to the compressable natute of air, when pulling on the starter and bringing the piston up to TDC. Measuring compression with the same gauge every time will give you relative values between porting / decking / gasket deleted cylinders (useful info) but cannot give you true (absolute) PSI chamber pressures unless you compensate for the extra guage tube length and volume. Is it worth it? Depends on what your outcome are targeted at. Chat GPT v4.0 should give you some formulas to work with if you ask it to!
They do it with race engines so why not measure the chambers on the saws? I am sure there is a degree of innaccuracy but i think this is in the realm of close enough. And i think i got all my values right on that attempt other than the wierdo exponent to calculate psi. The calculated comp ratio is probably more important for tuning than a conpression gauge measurement. Compression gauge is a diagnostic tool and not a precision measuring instrument. I intend on taking a scientific approach but i just havent quite got all the pieces gathered yet. The gauge i use has a schroeder valve in the threaded end so pressure equalizes in the tube. I use the same gauge every time because two gauges can be wildly off from one another.
First time I've seen a YT on this topic, one that I have wondered about myself.Congrats at a great attempt! Great to see a science-based approach to this issue. I am an Electrical Engineer by training (with a chainsaw obsession!) so the math is not a problem for me, but I agree in a large part with your approach with measuring chamber volume .
One point to note;
When measuring compression values with a PSI gauge, the volume of the tube from the spark plug hole to the gauge is included. In effect, you are increasing the chamber volume by the amount of air in the tube connected from the spark plug hole to the gauge. That extra volume will tend to lower the values displayed by the gauge. Because air is a compressible fluid, and the volume of the pressure gauge connection is larger than in real-world conditions, (i.e. without a pressure gauge attached) so you get a guage value LOWER than the operating conditions . Also note that there will be a (dynamic) pressure differential from the spark plug hole to the gauge measuring point, again due to the compressable natute of air, when pulling on the starter and bringing the piston up to TDC.
Measuring compression with the same gauge every time will give you relative values between porting / decking / gasket deleted cylinders (useful info) but cannot give you true (absolute) PSI chamber pressures unless you compensate for the extra guage tube length and volume. Is it worth it? Depends on what your outcome are targeted at. Chat GPT v4.0 should give you some formulas to work with if you ask it to!
They do it with race engines so why not measure the chambers on the saws? I am sure there is a degree of innaccuracy but i think this is in the realm of close enough. And i think i got all my values right on that attempt other than the wierdo exponent to calculate psi. The calculated comp ratio is probably more important for tuning than a conpression gauge measurement. Compression gauge is a diagnostic tool and not a precision measuring instrument. I intend on taking a scientific approach but i just havent quite got all the pieces gathered yet.
The gauge i use has a schroeder valve in the threaded end so pressure equalizes in the tube. I use the same gauge every time because two gauges can be wildly off from one another.
@@Super-Dave-Outdoors Thanks for your reply.
I agree; They're not a precision instument. Look forward to seeing your vids on your scientific approach.
Loving this type of content! Keep it coming!
I'll try, i am still figuring it all out myself but i am doing this for each motor i tear apart now.
That's some interesting stuff there. It'll be interesting to see how it equates to performance.
Compression definitely aids performance but there are so many more variables you cant judge performance based on compression alone.