9A Block Decking/Head Milling

[amalventano1@comcast.net (Allyn)]

Ron,
unless http://scirocco.dyndns.org/engine/ is wrong, the 9a block/head combo is
10.8:1, not 10:1.
either way, here are some cc numbers i whipped up for ya (for 9a):
cylinder volume: 496.07cc, total volume: 1984.29cc
using the following equation: combustion volume = cylinder volume/(comp ratio-1)
heres a chart i whipped up:
combustion volumes (tdc):
10.0:1 - 55.12cc
10.5:1 - 52.22cc
10.8:1 - 50.62cc
11.0:1 - 49.61cc
11.5:1 - 47.24cc
c/r starts going up sharply as you get further past 10:1. bore area is 53.46
cm^2, so 0.005" yields a combustion volume change of .6789cc. since c/r works in
a non-linear fashion, you'd have to compare math results to the c/r chart above
to get a good number, or just use the formula if you are going for exactness

as for the head gasket stuff, i know headgaskets.com has them available in
various thicknesses, but they are engineered for thicker, not thinner
applications (lowering c/r for high boost, etc).

no clue on thickness of a stock gasket. wish someone had some numbers there, as
getting the correct starting point for messing with c.r is key.

hth
Al

Allyn Malventano, ETC(SS), USN
87 Rieger GTO Scirocco 16v (daily driver, 180k, rocco #6)
86 Kamei Twin 16V Turbo Scirocco GTX ('it has begun', rocco #7)
86.5 Occo 16v Trailer (dotting 'i's across the country, rocco #8)
87 Jetta 8v Wolfsburg 2dr (daily driver, 260k, 0 rattles, original clutch,
driveshafts, wheels :)


----- Original Message -----
From: "'Cheapass' Ron Pieper" <rapieper@yahoo.com>
To: <scirocco-l@scirocco.org>
Sent: Thursday, August 22, 2002 11:01 AM
Subject: 9A Block Decking/Head Milling


> Hey all,
>
> Anyone have experience on how much I can (practically) deck the block
> and/or mill the head on a 9A 2.0L (assuming I'm using the 2.0L head)?
>
> How much will the CR raise for every, say, 0.005" off either surface?
> How much will I raise the risk of damage if interference should ever
> happen?
> Anyone have sources or experience regarding thinner head gaskets?
>
> Yes, I'm already starting with a 10:1 CR, and detonation is a
> concern...but please don't let that stop you from offering input to the
> above.
>
> TIA,
>
> Ron
>
> =====
> Cheapass Ron
> '87 Scirocco 16Victor
> Pet Peeve du jour:  It's GTI not GTi!!  Read the nameplate!  (US only)
>
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