Squish #'s

[huskihl]

Why is .015" to .025" a desirable #? Or is it a minimum #? Why would a 2 piece head be desirable if we can already machine and drop port timing? What if a given saw had sufficient compression at .030" or .050" squish?

 

[awol]

Wow, ok this may take a while!

Why is .015" to .025" a desirable #? Or is it a minimum #?
The ideal clearance is the least possible without letting the piston smack the head. This clearance varies between saws, depending on temp, speed, and the distance between the top of the piston and piston pin.


Why would a 2 piece head be desirable if we can already machine and drop port timing?
A removeble head allows for building a custom combustion chamber, and easier timing changes.


What if a given saw had sufficient compression at .030" or .050" squish?
A thinner squish area is desirable to push more of the fuel/air mixture out into the combustion chamber to help prevent preignition and give a better bang.

 

[Marshy]

Wow, ok this may take a while!

Why is .015" to .025" a desirable #? Or is it a minimum #?
The ideal clearance is the least possible without letting the piston smack the head. This clearance varies between saws, depending on temp, speed, and the distance between the top of the piston and piston pin.


Why would a 2 piece head be desirable if we can already machine and drop port timing?
A removeble head allows for building a custom combustion chamber, and easier timing changes.


What if a given saw had sufficient compression at .030" or .050" squish?
A thinner squish area is desirable to push more of the fuel/air mixture out into the combustion chamber to help prevent preignition and give a better bang.

And help cool the piston dome.

 

[David Young]

You want the least area that is safe. Normally 20 thou. It increases compression but maximizes squish velocity and as long as the band is not too wide. All is well. Even if the 20 thou only meant that you had 140 psi. It is a tuning of efficiency.


Kinda like ignition timing.