Heron Pistons and Larger Valves

[Alan Kramer]

I'm definitely getting confused here   According to the "Water-Cooled VW 
Performance Handbook" by Greg Raven, published by MBI, p.55, discussing the 
interchangeability of Heron motor parts   in column 2:

..."As previously mentioned, the Euro GTi's used this flat bottom [Heron] 
head in combination with very deep pistons. The combustion chamber is in the 
piston.  In most cases, the pistons that mate with this head cannot be 
interchanged with those from an American head without changing the head too. 
  The exception is that the pistons from the 1.6L GTi bolt into the 1.7 
liter motor, raising the CR to 9.2:1.  Other than this, you will normall use 
flat-top (or shallow dished) pistons with American style heads and the deep 
dished pistons w/ the Heron heads."

Now Bruce is entirely correct that the 1.6L GTi motor is a 80mm stroke and 
the 1.7 L motor is a 86.4mm stroke.  The WE code 5 cylinder is 86.4mm as 
well...  All the engines we are talking about are 79.5mm bore.  Therefore, 
if the Heron piston can't work on a WE code motor then it definitely can't 
work on a VW 1.7 liter motor 'cause they're the same cylinder dimensionally 
(bore & stroke)...

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?

Alan



>From: "Bruce Bell" <bbell04 at attglobal.net>
>Reply-To: <bbell at surview.com>
>To: "Alan Kramer" <ackramer at hotmail.com>, <quattro at audifans.com>
>Subject: RE: Heron Pistons and Larger Valves
>Date: Mon, 18 Dec 2000 16:17:35 -0700
>
>Careful...
>
>Those 1588 cc VW's used an 80 mm stroke. If you try to use these
>pistons with your WE then about 3.2mm of those piston will be
>above the block.  The heron pistons have a very deep dish,
>similar to the dish in the WX/WR motors used in the Urq's. I
>can't see how the heron could possibly raise the CR.
>
>If you are going through this much trouble use the pistons from
>an 85 or 86 GTI/GLI and  bore the block to 81.5 mm. This should
>yield you a 10:1 CR. which you can lower by unshrouding the
>valves while cleaning up the combustion chamber.
>
>Bruce
>


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