Date:         Wed, 26 Nov 2003 13:27:07 -0500
Reply-To:     kdlewis_wasting_time@ACCESS4LESS.NET
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Ken Lewis <kdlewis_wasting_time@ACCESS4LESS.NET>
Subject:      Re: Compression Ratios, mixing Heads.
Comments: To: ROBERT DONALDS <donalds1@VERIZON.NET>

Bob,
Start with the basic formula:

CR= (Cylinder Displacement + Combustion Chamber)/Combustion
Chamber

    For displacement I used the volume swept by one piston.

    For combustion chamber I lumped together all the volume
that is left over i.e. the inverted dome in the piston, the
clearance area you speak of, the volume of the head gasket
and the volume in the head. Since these areas are small and
acurracy might suffer, I only introuced the head volume
measurement I made and solved the equation for those
unknowns. In other words I substituted:

Combustion Chamber = Head volume + X

into the above equation and solved for X. All the other
numbers came out of the Bentley.

CR=9.0
Displacement= 2109cc4= 527.25cc
and 16cc for the  2.1L head volume I measured.

Solving I arrived at X= ~50cc for a factory engine.

I then inserted this value for X and 12 CC for the 1.9L
engine into the first equation and arrived at a compression
ratio of 9.5:1.

If you are saying the replacement pistons have a smaller
clearance area than stock, then the compression ratio could
be dangerously high! That is a variable I did not take into
account. Un-shrouding the intake valves, like you suggest,
is a very good idea from a CR standpoint since this
increases combustion volume and hence, reduces CR.

Ken


----- Original Message Follows -----
> Ken
> It was not clear in your explanation if you measured and
> took into account the distance from the top of the
> cylinder to the piston. there is a 1mm difference between
> OEM and cofap pistons, cofaps being the deeper of the two
> Bob
>
>
>
>
>
> ----- Original Message -----
> From: "Ken Lewis" <kdlewis_wasting_time@ACCESS4LESS.NET>
> To: <vanagon@GERRY.VANAGON.COM>
> Sent: Tuesday, November 25, 2003 9:45 PM
> Subject: Compression Ratios
>
>
> I tried to calculate the effect of using 1.9L head on a
> 2.1L engine. The results are at
> http://neksiwel.20m.com/custom.html at the bottom of the
> page. Ken Lewis
> 86 Transporter Crew Cab
> 60 356 T-5 Porsche
> http://neksiwel.20m.com/
> Vanagon tech, pixs, O2 monitor gadget

Ken Lewis
86 Transporter Crew Cab, 60 T-5 Coupe
http://neksiwel.20m.com/   O2 sensor monitor gadget, my
cars, Vanagon Tech
http://EB03.20m.com/  Everybus 2003 pictures