According to a link above, I think you can use a 13.5 CR and still run 25% nitro or so. That means if you use less nitro, you can get an even higher CR. I don't know that the engine itself will allow it due to the valves. 13.5 would still be very nice.
I bet you can really feel it when turning the engine over by hand.
ORIGINAL: canardlover
RVM, yes it was good to see that it broke at the big end and not along one of the "cheese holes"...!
I still intend to reach CR 13.5 as proposed by downunder et al. but have so far only obtained CR=12.5 on my most modified engine. This .56 has the "skeleton" piston and other "guts" as shown in post #22 above and has been milled -1.3mm from the case. I have flown it twice in my Sig Cougar just recently and this engine runs better than ever before so I intend to continue in incremental steps towards 13.5 as time permits.
I´m still not sure if CR 13.5 is possible in a Saito.56 without parts hitting each other....downunder, can you chip in here from your experience/sources..??
As an example we modified an old Saito.40 by arbitrarily milling -1.0mm and that turned out to be exactly what was possible with its piston just about hitting the glow plug. CR on that .40 increased from 7.1 to 9.3 in the process but we have not yet had the time to run it.
....anyway CR research continues....
.....RVM, how are you doing with your .82...??....Cheers/Harald