Fivegreen, you're right about the Christen valve.
If you have a Pitts, that chubby fuselage will generate enough lift to maintain knife edge, a real delight.
On my SU-29 it is possible to maintain knife edge for quite a while with enough speed, especially if you keep the nose 15-20 degrees over the horizon..
Radials having a separate oil tank (Dry sump) do keep positive oil pressure all over the aerobatic flight envelope.
The separate SU-29 cylindrical tank bolted to the firewall has a swiveling arm in the form of a conrod rotating at 360 degress picking oil into the lines whatever you do. A bit like a model airplane with those plastic bottle reservoirs fitted with a steel tube attached to the flexible gasoline hose. Steel tube with a counterweight at its end moving freely around to gravity in the same direction as the fuel content.
Rightly so Rudderrudder !!! reciprocating parts are subject to considerable load, but while pushing an engine with max 1000 RPM to 1700 (70%) might send those pistons into free space and at best having the valves take a bite on pistons heads, Pushing a Lyco from 2700 to 3000 (10%) might not.
It is possible to overrev an engine fitted with a constant speed prop and adjusted governor to 2900-3000 RPM
In competition, ( and often in training) unlimited category aerobatics all engines are firewalled all the time at 2800-3000 RPM.. But those flat six lyco's don't usually make it to TBO. They endure too much wear, i believe not so much because of overspeeding but mostly due to lubrication wet sump issues..
Different story with the Russian radials, they are supercharged so no more than 100% power.. ( I use 82% continuous don't need more) Manuals say max continuous permissible is...82% for 5 min. Max 10% of TT.
But the folks who compete and I know quite a few of them use... 100% ALL THE TIME....To my knowledge there was never a problem.
The only major issues with Sukhois and Yaks as far as engines are concerned, are hydraulic locks failures, and believe me there have been a lot of them.
There is a pre engine start engine procedure to respect to the letter, you don't do it and the engine will bite you sooner or later. Installation of manifold drain kits and proper prop cycling help avoid that.
I remember driving my Honda bike 20 years ago, and sometimes while pushing the engine, I often missed a gear while shifting... winding the RPM needle .....another revolution..... Take that pistons and valves !!! Nevertheless as I always took good care of my engine by warming it up carefully, breaking it in when new in a religious way, despite what manuals say nowadays..
Never had any failures, never had to add a drop of oil in between oil changes...