If you look at the throughput area of the AMT wheel you can see it is much less than the Wren 66, so although they are of a similar o/d the actual 'working' area is much reduced. The AMT wheel is designed/built from the outset for high rpm(150k+) the same as the 60mm Garrett compressor wheel up front. I burned many litres of fuel at max rpm before commiting the engine to an airframe.

The shaft and turbine wheel were machined/ground to within a couple of microns runout after a few heat cycles to allow the hot components to 'settle'. I then spent an evening concentrating on getting the rotor balance as good as my equipment would allow.

The turbine wheel/ngv tip clearance is just enough to avoid any 'rubbing', this I am told can lead to better fuel efficiency.

I thought the engine would sound similar in the air to an AMT but it's completely different, possibly due to the turned from solid alloy casing.

Next project engine will use the wheel on the right Shaft has just been turned ready for final grinding to size.

Rob.