I've worked backwards from a bunch of available information on the various VW diesel engines and get around 18.5:1 for a 1.9 head on a 1.6 block. I don't have the stuff at my finger tips, but i'm faily confident in my mathematicle abilities to be satisfied. If someone else want do do the research and comes up with 19:1, i will not be up set. Its in the ball park, and it will do what I want. There are poeple that have gone befor my in this endevour. I am by no means the pioneer here.
My main goal for ruducing the CR is to reduce the load on the rods, bearings, head and whetever else, so I can run more boost and fuel. Its a summer only diesel, and it still should start with a lower CR. It might start even better with the piston clearence set properly. If the fuel milage drops, I will not be concerned. Its a diesel power go kart in my eyes. A nifty toy.
Since I have blown off the piston protrusion measurement, I have no idea where the gasket situation is.
What I do know is this engine has always had a less than gorgious start, even with everything bone stock, and all the glow stuff PERFECT. With everything essentially brand new, and set spot on, and nothing else weirded out, it points to the only variable I did not verify: piston protrusion, and hence the proper gasket.
Ive been all over the fuel thing. Was even running 24+PSI with a soot cloud that blacked out the light and warmth from the sun. Its a little more conservative now, but in no way pedestrian.
I hope to get to this head swap soon, and I'll gauren-gosh-darn-tee that I'll measure piston protrusion. Its was appearently a big enough deal for the engine OEM to go through a few hoops to get it right, and thats good enough for me.
As a matter of fact, i'm gonig to determine what the squish is, and i might make it tighter if i can get away with it.
Here is some squish stuff that took me only a short time to find. I don't think the detonation thing applies to us, but piston cooling, and turbulence are right up our alley:
What does having the squish clearance close do? It makes the compressed charge between the squish band and the top of the piston (at the top of the stroke) thin, thus allowing for quicker heat transfer between the piston and the squish band. This clearance change will produce MORE HP, MORE TORQUE, and the engine will not have to work as hard. You will be able to run a richer setting, come off the turns faster, launch better, pull a bigger prop, run cooler and run faster! This is probably one of the 3 biggest failings of the Novice Boater!
One of the most important items in the design of a good combustion chamber is the squish band. I believe that a flat squish band produces much more power than an angled squish band. The flat squish band head has a flat area (squish band) around the perimeter of the head which comes in close proximity to the piston at top dead center. This squish band is designed to keep the layer of combustion mist very thin, in order to let heat travel quickly from a hot piston to a cooler combustion chamber (head). The thinner this layer (the closer the head clearance), the better this heat transfer is accomplished. If your head has its squish band to far away from the piston at TDC and the compression ratio is high, you will get pre-detonation (knock). You can tell if this is happening by looking at the squish band. If it looks like it has been lightly sand blasted, it is pre-detonating. Most people when they see this pre-detonation automatically raise their squish band piston clearance. That is the WRONG WAY!
Quench, or squish area is typically the flat area on the top of the piston that's almost level with the top of the block deck. It must have a corresponding flat area on the deck surface of the head to qualify as quench.
If you look at a combustion chamber, you will usually see these flat areas, and they will have the volume of the actual combustion chamber between them. When the piston is compressing the mixture, as the piston nears the head, the flat areas on the head and piston come together and force the mixture from those areas to "squish" into the chamber, where the spark plug and burning mixture reside, so you achieve a more complete burn.
The quench area also runs cooler than the rest of the chamber / piston. These lower temperatures are where the "quench" comes from.
When properly designed, the quench areas can have a tremendous effect on the quality of combustion, and allow higher compression ratios, and due to this they are considered "artificial octane" by scientific types.
Bottom line is "properly designed, quench is good