Here is what I've been able to discover today;

Jack McAllister in Washington state has replaced his turbocharger compressor with parts from the Piper Mirage (Lycoming). This was done at Approved Turbo Components (ATC) in Visalia California. (Speak with Mary). It has no interference with Dolly Parton cheeks. This has many positive benefits, one of which is lowered inlet temperatures into the throttle body as well as increased manifold pressure availability at altitude. He also has increased the air filter area by using a K & N Extreme Top increasing the filter area from 57 inches to 186 in.². He does not ever see a filter bypass light on take off.

Spoke with Monte Barrett. He did quite a bit of work with Jack McAllister and Brent Reagan with regards to turbocharger's. He said that we should get the bigger compressors.

Then I spoke with Bob Minnis. He has outstanding credentials. He was at Continental and was the TRIO 550 / Lancair expert. Bob Minnis says to prevent this "backfire", use 2500 RPM IN CRUISE ABOVE 20,000 FEET. 

So IMHO-- and to sum this all up;

Magnetos--if you have ever lost magneto pressurization and flown above (let's just say 15,000) and felt a stumble or misfire--they both should be overhauled. Carbon tracking once started on the distributor block can never be removed.

Here's my suggestion, if you have this problem (random backfire in cruise) make sure your ignition system is pressurized/and sanitary --then if all checks OK and it continues, check exhaust system, turbine wheel for erosion, compressor wheel for damage, and if all checks OK, reduce manifold pressure--increase rpm, until it does not repeat itself. Then at the next Turbo overhaul, get the bigger compressor. Apparently there is a demand for the smaller compressors that we have --and if it is in good shape they will exchange your parts for the bigger Malibu compressors for little or no cost.

Charlie K.