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 |
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