need compression reduction info

[jdbubb@ix.netcom.com (Dan Bubb)]

Jonas:
I'm with you here all the way except....
using 8v pistons with 16V heads.
The squish area on a 16V is at the front of the chamber. The squish portion
of the 8V piston is on the rear of the piston. The combination produces a
big open chamber with no squish, poor turbulence, poor combustion.
Gotta wonder about reversing the piston, but even then it would be one
pathetic combustion chamber!
Dan

----- Original Message -----
From: Jonas K. <jkarlsso@metabolex.com>
To: Anthony Pelletier <vwnuts@yahoo.com>; scirocco list
<scirocco-l@scirocco.org>
Sent: Friday, January 11, 2002 4:28 PM
Subject: Re: need compression reduction info


> On 1/11/02 8:38 AM, "Anthony Pelletier" <vwnuts@yahoo.com> wrote:
>
> > I was wondering if
> > anyone knew what it would take to drop the compression
> > of a 1.8 16v from the stock 10:1 to 9:1?
>
> Tony,
>
> The only reason I can think of to drop the compression is for turbo
purposes
> (maybe NOS?).
>
> If you are installing a turbo system, I HIGHLY recommend buying Corky
Bell's
> book "Maximum Boost". It details everything you want to know, including
how
> to calculate compression ratio ((Total volume at BDC)/(total volume at
> TDC)).
>
> This also covers how to properly drop compression to accommodate a turbo.
> But until you get the book, here's what he says (paraphrased)
>
> ----
> Modern motors use a squish area on the piston to swirl around the air/fuel
> mixture, thus reducing detonation. This Squish area must be preserved in
> order to keep the turbo motor from knocking. Basically the squish area is
> the outer1-2mm of the piston face.
>
> Steps of reducing compression ratio that preserve the squish area are:
> removing metal from the head side of the combustion chamber; using valves
> that are more concave; removing metal from the piston face (not touching
the
> outer rim); using pistons that create a larger combustion chamber (factory
> or custom). Anytime metal is removed one must make sure that structural
> integrity is not compromised.
>
> Similarly, ways of reducing compression that are NOT valid are, using
> shorter rods, or using a thicker headgasket.
>
> Tampering with the squish area can be so bad that the car will knock more
> with the lower compression that it would have if everything was left
alone.
> -----
>
> Something to think about is that since the 16v motor has more volume in
the
> head than the 8v, one can use 10:1 8v pistons to get at a fairly low
> compression ratio. I think something like 7.5:1 or so. Shave some off the
> head and you can get it back up some. These will retain the squish area
> AFAIK. To get to a 9:1, the only way I can think of is to buy custom
> pistons. A worthwhile investment if you're serious.
>
> Putting in a 2.0l motor won't change the compression much (if at all).
>
> HTH
> Jonas
>
>
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