Pelo contexto dado à pergunta, penso que se trata antes de "squish band".

The Squish Band or "Quench" is defined as that area between the flat of the piston and the flat of the cylinder head at top dead center (TDC). On the compression stroke, as the piston approaches TDC, the compressed mixture of fuel and air is "squished" to the remaining space of the combustion chamber where the spark plug and valves reside. The "squeezing" of the mixture creates turbulence and is expected to promote a better and more complete combustion.

http://www.rbracing-rsr.com/squishcalc1.html

Outros sites que tratam da squish band:

Squish band in a combustion chamber
This is the "squish band". The effective squish angle in this drawing is probably
a few degrees (this would be considered tapered squish). ...
www.muller.net/mullermachine/docs/squish1.html

©2004 Model Engine Corporation of America, All rights reserved ...
The squash or squish band is the clearance between the head and the top of the
piston. ... The squish band is usually set between .016" and .022" ...
www.mecoa.com/faq/squish/squish.htm

squish band ..squish head => área de compressão

..:: SIX SPEED - Techspeed ::.. -
... Medir o espaço entre o pistão e o cabeçote é critico já que a medição deve ser feita pelo lado mais exteno do "squish band" ( o fundo da câmara não é paralelo ao pistão) Portanto a partir da taxa original dos motores ( 16% .15 e .12 / 25% .21) a dica é ler a vela (glowplug) ...
sixspeed.com.br/lista_techspeed.asp?id=9

DiagHomelite30Std -
... Transferência abre: 60° APMI. fecha: 60° DPMI. duração: 120°. Ponto: Squish band:
2,00 mm. Compressão: 90 PSI. Copyright © 2000 - Carlos Andrade.
www.shark-racing.com/Portugues/Tecnica/DiagHomelite30Std.ht...