Compression Ratio, Will I be able to tell the difference? Options

[sdoolin]

Rebuilding(ish) my 2056. On my first build I was able to achieve a compression ratio of very nearly 9.0:1. With this build, I am having to add .020 spacers below the jugs to get any measurable deck height in the jugs. I am calculating a compression ratio of 8.6:1.

Will I notice the loss in compression ratio?

[technicalninja]

You need AT LEAST .036 with cast and .040+ with forged pistons.

This is piston top to cylinder top (deck height).

I am assuming you are not using fire rings (shims on the head side of things).

Any less and you risk piston to head contact.

This is fatal!

The compression difference will be tiny.

Now, for proper quench action you want "as tight as possible without P-H contact".

The deck height MUST be measured in line with the pin.

The more piston to wall clearance you have the more deck clearance you need.

Run tight cast clearances and you can go tighter than .040.

Run loose forged clearance and you will need more.

Larger bores need more as well.

For performance engines I want to be ALWAYS less than .045...