Volvo: volvo 850 compression test, unleaded petrol, volvo dealer

Question
Hi there.  
About a year ago, I had my volvo dealer run a compression test on my 1994 850 non turbo engine.  The engine has now done 151,000 km.  
All 5 cylinders were around 140 psi, with the lowest reading 130psi.  Last week, I had them run another compression test (I've been using high octane unleaded petrol) and the readings came in at 175psi for all 5 cylinders.
My questions are
1. why the variation betweeen readings? My dealer said this could  be due to the fact I've been using  high octaine petrol which cleans the valves.
2. Is 175 psi for each cylinder a good reading?
Thank you so much for taking the time to read this.
Leigh

Answer
Leigh,
Compression pressure should measure 188-218 psi with engine hot.

The maximum difference between cylinder compression pressures should be 28 psi.

So your car seems in real good condition. Yes if the valves were dirty and not closing well enough that could account for the poor compression before you change fuel types.