Heron Pistons and Larger Valves

Ti Kan ti at amb.org
Tue Dec 19 16:25:35 EST 2000

Alan Kramer writes:
> Now here's the part I don't either understand:  How in the heck does a deep 
> dished piston increase the C/R when it replaces a shallow-dished piston?   
> Can anyone explain this, or am I reading the above paragraph incorrectly?

The heron deep dish pistons don't increase CR by themselves.  Their use in
conjunction with the special cylinder heads that have flat bottoms (i.e.,
does not contain the combustion chamber) yields a high CR motor.  As you
said, this is a special combo that has the combustion chamber located
entirely in the piston dish.

The VW 1.6 and 1.7 motors have the same bore, the 1.7 having a larger stroke.
In the special flat-bottom head + heron 1.6 engine, if you were to install
the 1.7 crank you'd get a a CR boost because the piston will travel closer
to the head.

Your existing head is not one of those with the flat bottom variety,
therefore you cannot use the heron pistons.  Non flat-bottom heads
with the heron pistons would increase the combustion chamber size in a
big way, *decreasing* CR.

01 S4 2.7 biturbo quattro
84 5000S 2.1 turbo
80 4000 2.0
96 A4 2.8 quattro (sold but not forgotten)
    ///  Ti Kan                Vorsprung durch Technik
   ///   AMB Research Laboratories, Sunnyvale, CA. USA
  ///    ti at amb.org
 //////  http://www.ibiblio.org/tkan/

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