Quote from John Slade
"Just as a data point, I took the Kitty up to 190 kts (220 mph) indicated at 11,500' (straight and level) incrementing by 5 knots then testing for flutter all the way. There was no sign of flutter whatsoever, in fact the engine seemed to hit a sweet spot as it got to 6100 rpm and was quieter and smoother than usual. I think I got to around 6200 or 6300. (2.17 ratio) I had plenty of throttle left and, if I remember right, was running at about 43 MAP. After a minute or two I decided that was quite enough for one day and throttled back."
I find it interesting that you have gone to alot of time and expense to compress air using the exhaust gases, only to restrict that compressed air from entering the manifold using a throttle body.
If you have the throttle closed 50% and are still indicating 40 "inches MAP, then the turbocharger is generating perhaps ??" inches. At 11,000 feet the air is around 20" inches MAP, and thus a compression ratio of perhaps 4:1. Which I believe will put the compressor into or close to overspeed and surge. A larger turbo has of course alleviated the problem, by increasing the "thumb print" of the compressor map, and thus bringing the line back on to the graph.
If the throttle was fully opened first, followed by the wastegate, then the pressure and temperature passing through the exhaust gas turbine will be reduced, leading to a reduction in turbine RPM, and thus wear and tear.
Two levers, very simple.
This is the system fitted to TIO - lyconentals in birds such as the Piper Seneca.
My 20 Pence ...
I would be interested to hear thoughts on this ...
all the best