Deck height question

[fred cook]

I'm building a 3.3SS engine using LN 100mm cylinders and Mahle 10.1:1 pistons. The deck height on cyl. 1 measures 1.1mm using one 0.25mm shim. Options are 1) build as is, 2) add a second 0.25 shim, 3) order a set of 0.50mm shims. The dome of the piston extends approximately 11mm into the combustion chamber at TDC. The combustion chamber in the head is approximately 27mm deep so there is a generous amount of clearance between the piston and head. Since the pistons are "only" 10.1:1,
I would like to preserve as much compression as possible.

[MBruns]

I would leave it at 1.1mm deck, if you have the ability you should pour the head vol. and the dome vol. to see exactly what you have for CR, also check your valve to piston clear. to be sure it good. If you can pour the dome/head vol. send me the info and I can calculate that for you if you need.
Mike Bruns

[fred cook]

Originally Posted by MBruns

I would leave it at 1.1mm deck, if you have the ability you should pour the head vol. and the dome vol. to see exactly what you have for CR, also check your valve to piston clear. to be sure it good. If you can pour the dome/head vol. send me the info and I can calculate that for you if you need.
Mike Bruns

Mike, thanks for the input. I stayed up late last night reading about 10 years worth of threads on the deck height issue and finally decided to stay at the 1.1mm height. I installed a piston/cylinder on the right side this morning (#6) to check and got the same results. I found a significant number of folks that subscribe to the theory that a good deck height would be in the 1.0mm neighborhood. The heads that I am using came off a track engine that was running slightly better than 11:1 compression ratio and the combustion chambers have been beveled for additional piston clearance. Can you calculate compression ratio with a dimensional profile of the piston head and combustion chamber? If so, I can pull those numbers off the pistons and heads and send them to you.

[MBruns]

You really need to CC the vol. of the dome and chamber to get an accurate calc. You can send me a complete head,cyl with a piston and rings if you like and I can do it.
Mike Bruns

[fred cook]

Originally Posted by MBruns

You really need to CC the vol. of the dome and chamber to get an accurate calc. You can send me a complete head,cyl with a piston and rings if you like and I can do it.
Mike Bruns

Too late! the pistons, cylinders and heads are already assembled! I believe that I had the guys at Xtreme Cylinder Heads CC the heads, so it is just a matter of finding that info in my files. I'm pretty sure that I can calculate the volume of a sphere segment. Given the chord length and height (which I have) the rest should not be too difficult.

[304065]

Fred, you can calculate a spherical cap, but then figuring out how to deduct for the valve pockets is the challenge.

Grady tells us how he did it assembled but that involves greasing rings and valves.

http://forums.pelicanparts.com/911-engine-rebuilding-forum/294214-9-8-10-1-a-2.html

[fred cook]

Originally Posted by 304065

Fred, you can calculate a spherical cap, but then figuring out how to deduct for the valve pockets is the challenge.

Grady tells us how he did it assembled but that involves greasing rings and valves.

http://forums.pelicanparts.com/911-engine-rebuilding-forum/294214-9-8-10-1-a-2.html

Somewhere in my notes I have the CC'd volume of the cylinder heads. I had the heads rebuilt by Xtreme Cylinder Heads in Florida and had them CC the heads while they had them. Now the trick will be finding it!