[Grady Clay]

I agree, these pistons look like they are cut for very large diameter valves and possibly high lift and duration cams.
My point is that you must know.

This looks like a very nice set of 84 mm (or are they 85 mm?) forged pistons and Biral cylinders.
The pistons appear to have unnecessarily large valve pockets.
There is a building principal to have the valve cut-out just ‘large enough’ and not give anything away by having them too large.

‘Giving something away’ is the trade off with CR and piston crown height.
The larger piston crown height raises the CR to the desired number.
The valve cut-out lowers the CR.
With a ‘too large’ valve cut-out, the piston crown height must be unnecessarily higher to get the proper CR.
High crown height is undesirable because it interferes with the flame travel during combustion.
This is particularly true with single plug engines. (Looking at these pistons, they would greatly benefit from twin ignition.)

What is the maximum size (diameter) valve that will fit in these valve cut-outs?
This should be about 1-2 mm larger than the 46 mm intake and 40 mm exhaust valves for your 2.2 engine.
Larger cut-out unnecessarily lowers the CR requiring an unnecessarily higher crown height.


Have you decided on what CR you intend to use?
That number is dependent on your use, access to high octane fuel and a number of other factors.
The CR is also dependent on your choice of cams.
You can effectively use higher CR with an S cam than with an E cam.


Does your 2.2E still have the MFI?
If so, it is undesirable to stray far from the 911E cams in the engine unless you change the space cam in the MFI pump.
The head intake ports, cams, throttle bodies and stacks are all size-matched to the space cam in the pump.
Carburetors are ‘smarter’ (just not as ‘cool’) and meter fuel in proportion to the air flow – whatever parts you use.
Well matched MFI produces more power and better over the entire rpm range.

I hope this helps.
Search the 911 Engine Rebuilding Forum. There has been a lot of this technical discussion.

Best,
Grady