Modding: What Does "Squish" Mean?

[StihlRockin']

I see a few references to people talking about squish and come to the conclusion it's some sort of minute precise measurement, but not sure for what. Using the search I see more talk of it... not much explaining what it is.

So, what is squish and why if I'm going to mod, feel like it's something I need to be concerned about?

StihlRockin'

 

[sawinredneck]

It's the cold clearance between the top of the piston and bottom of the cylinder. It's mainly important when removing the base gasket on a modded saw.
The easiest way to measre is to remove the muffler, make sure the cyl. bolts are tight and slid a piece of solder in the exh. port. Run the piston through one complete cycle then measure how thick the solder is.
It varies on how big the saw is, but ussually .022" is a decent amount of clearance.

 

[Goat]

Squish is the clearence between the top of the piston and the top of the cylinder when the piston is at TDC.

On the compression stroke the mixture is squished into the combustion chamber space were the spark pulg resides. The squeezing of the mixture creates turbulence and is expected to create a homogenous mixture, promoting better and more complete combustion.

You want to make sure that your squish is not too tight otherwise the piston might contact the cylinder top. Keep in mind carbon building up on pistion and inside the CC. Rule is 0.020" of squish.

 

[stihl 440]

thanks

Squish is the clearence between the top of the piston and the top of the cylinder when the piston is at TDC.

On the compression stroke the mixture is squished into the combustion chamber space were the spark pulg resides. The squeezing of the mixture creates turbulence and is expected to create a homogenous mixture, promoting better and more complete combustion.

You want to make sure that your squish is not too tight otherwise the piston might contact the cylinder top. Keep in mind carbon building up on pistion and inside the CC. Rule is 0.020" of squish.

WOW!! I never knew this either, but now I do because of that post, THANKS!!!:greenchainsaw:

 

[Freakingstang]

Squish is kinda like the static compression ratio. The less squish you have, the more compression..When modding, you typically try to raise the static compression, by deceaseing squish. A good rule of thumb is 17-20 thou.

Some guys make it more complicated than it really is. There is a band around the cylinder. This is the squish band, it is at the bottom of the combustion chamber. As the piston comes up on the compression stroke, the squish band is the machined surface that keeps compression of the gases consistent. It is also lower than the compbustion chamber so that the combustion is minimized to a controlled environment. It keeps the fire in the chamber, instead of leaking out and firing all over the piston surface

Combustion chamber size also has an influence on performance when modding. but there is not much you can do to one that is stock, although a lot of guys will make a custom head to get the desired combustion chamber.

 

[StihlRockin']

Excellent feedback guys. Now I understand what it refers to and see it's something I won't have to worry about anytime soon, but when the day comes, I'll be more informed. Thanks a lot for the answers. Quite enlightening.

StihlRockin'