[Lapkritis]

Originally Posted by 304065

Walt is also wrong. He's a great machinist with a great reputation, but he is absolutely wrong when he uses the term "deck height" to describe, in great detail, the measurement of piston-to-cylinder clearance.

Suppose you and he are correct. Suppose you remove a cylinder head and use an angle grinder to remove material from the top of the piston. You have increased piston-to-cylinder head clearance, right? But you haven't altered the deck height in the slightest.

Take a look at the formula for calculating compression ratio. You can find it in Bruce Anderson's book, but it's a very common formula. Look at the deck height parameter and note how the overall compression ratio varies with deck height, which is a function of stroke, spigot height, cylinder height, rod length and compression height. Piston to cylinder head clearance has nothing to do with that calculation and is not used in calculating compression ratio.

Look at the definition of compression distance, this is defined as the distance between the centerline of the pin boss and the deck of the piston. It is not a function of dome height, or piston to cylinder clearance.

Hope that clears it up.

Uh, wow. Piston design and chamber design specifically in CC volume certainly do impact compression significantly. Quench effect and ignition be dismissed, removing material from a piston and leaving other variables unchanged will decrease compression. This is common knowledge for anyone who works on an engine with carbon build up in the combustion chamber and knows about the pinging/detonation that results.

Piston to head and relation to deck height... who would seriously take a grinder to a piston?