Dummy Question: "What is Squish?"

[West Texas]

I'm obviously not an engineer. I keep reading about squish and do not know exactly what that means. Did a search on AS and it just gave me more talk about the amount of squish. It's obviously important in rebuild's etc. but precisely what is 'squish'? And how is it measured?

 

[bump_r]

In automotive terms, there is an area in the combustion chamber where the piston-to-cylinder head space is much smaller than the remaining area. Ever see a typical 76 cc Chevy small-block head? Notice the "D"-saped "hollow" which would be direclty above the piston? The flat spot adjacent thereto is the squish area. This is where the fuel charge is, well, squished during the compression stroke. Flame-front propogation is engineered by volume, shape and placement of the squish area. Get into domed pistons, hemispherical head designs, negative deck heights, and other engineering voodoo it gets more complicated. In this forum the term is used pretty much to describe the static piston-to-head clearance.

 

[Lakeside53]

It's what happens to your finger when you put it in the exhaust port and then rotate the flywheel.. true... and it hurts..

 

[MacDaddy]

I alway thought it was a big yellow pumpkin HAHA

 

[Lakeside53]

I alway thought it was a big yellow pumpkin HAHA

Only a MAC guy would think yellow

 

[Lakeside53]

Now you have me confused.

What is the difference between 'squish' and 'shear'?

Squish is the part of the the finger is still attached, shear is.. yes, you can get sheared and squished..

let me rephrase - "squish is when you put your pinky in the plug hole and pull the engine over"... how's that!

 

[West Texas]

I appreciate the informative reply Bump_r. Thanks. And to the rest of you guys :censored:

 

[NovaMan]

Another term for squish is quench. The thing about quench is that as the piston comes up to the head, the air/fuel mixture gets squished out of the quench area and shoots into the combustion chamber, generating turbulence and mixing, which help flame front propagation. If the piston to head clearance (quench) is too large, you won't get enough turbulence and mixing, and if the piston is too close to the head, some of the mixture may effectively get trapped and not burned efficiently. At least that's how I understand it.