4age bigport head: port & polish

[jamiemirror]

Yes, open and close type combustion chambers.
http://www.billzilla.org/engcombust.htm

Read this. And take a look at Formula Atlantic prepared head.

Quote:Also important is the squish areas, for best power. A 'squish area' is a part of the combustion shamber that is made to very nearly come into contact with the piston when the piston is at top dead centre. There's usually less than 0.030" (0.75mm) clearance in these areas in such cases. What they do is cause the combusting gasses to rapidly travel towards the centre of the combustion chamber (or where ever intended) and increase turbulence, thus increasing the combustion rate.
It's increasingly important as the revs build up, so more attention is needed. Ford/Cosworth experimented extensively with so-called open and closed combustion chambers, and found that a well designed closed chamber always made more power. (In a naturally aspirated engine, at least)

I support Bill with suggestion that squish area will provide faster combustion rate (not too good English, sorry) - and this is important especialy in hi-rev engine.

PS: I modified your drawing a little by ADDING the squish areas and showing their role (see red arrows - this is faster gas/fuel mix flow due to squish areas presence).