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I have 2 of the same engines with a specified compression ratio of 12:1 and compression range of 6.5-10 bar.

When a compression measurement was taken, a range of 15.5-16.2 bar on one engine and 13.9-15.2 on the other was found.

What is the significance and likely cause of the difference to the specification..?

Hi there,
I would try a different gauge and see if that changes anything. It does sound a little strange that the actual compression achieved is a lot higher than the standard specs.
Are these engines standard? Or has the heads been skimmed or different crank/ pistons been fitted?
A higher compression ratio is usually sought in non-turbo engines for better performance.

As far as I'm aware both engines are standard and definitely non-turbo, although they are high performance engines hence the high compression ratio.

The one with the lower readings is a 2008 (unknown km) while the other is 2013 (60000km). I have data print-outs if they mean anything to you.

Techs reckon high bar reading is due to carbon build-up.

Hi there,
There are quite a few things that can affect compression readings, usually you would find the readings of an old standard engine to be lower than factory specs. If there was a bit of oil in the cylinders, this can raise the compression readings too. I would be inclined to recheck the origin of the specs and gauge used and start again with determining a reference for the readings you have. There is a huge difference from a spec showing a max compression of 145psi and your engine showing a max of 234.9psi. As far as the difference between the high and low for each engine, it would seem to be acceptable.

Cheers..!