Knock Detection

Frederic Breitwieser frederic.breitwieser at mcione.com
Fri Nov 7 01:58:46 GMT 1997


>Fred, when you refer to "edges", are you referring to the edges of the
>combustion chamber that meet the head gasket?  Or, possibly any areas of the
>combustion chamber that might not have a smooth radius but maybe a 90 degree
>angle?

Hay Chief!

Detonation tends to occur at sharp points or edges in the cylinder region,
more towards the top of the cylinder as its hotter there, due to the way
the combustion process seems to work (twisted wedge heads for example
change this drastically).  Anyway, if you flip your heads over, your valves
on most engines are recessed, in an oval or trapizoidal indentation, which
is shallow, but has sharp 90 degree edges.  Also, piston tops sometimes
have what I call "valve notches" or other surface patterns/shapes that also
might have straight edges.

The idea behind radiousing is to round off all these straight edges, thus
encouraging hot spots to dissipate easier and quicker.  Quite honestly,
this is above my understanding, but I'm repeating what was explained to me
by a pal of mine who builds race engines.

Something to keep in mind however, if you shave material out of the chamber
& pistons to round off all the edges, you are effectively lowering your
compression ratio a little bit, if building an engine, this should be
taking into consideration so you can achieve your desired compression ratio.

>I am interested in port and polishing my heads in the future and would like
>to learn as much about this as possible.

I have two friends who are very knowledgable in their own field, one
engines, one body work, however for the life of me I can't get either of
them to buy a PC.  LOL.


Frederic Breitwieser
Homebrew Automotive Mailing List
Bridgeport, CT 06606
http://www.geocities.com/MotorCity/Downs/4605/index.html
1989 AG Hummer 4-Door
1993 Supercharged Lincoln Continental
2000 Mid-Engine Sports Car <smile>

Seeking Info on: GM Tubular Upper and Lower A-Arms





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