I did the variable geometry turbo on my Miata.
It didn't live for long - it doesn't have a wastegate, so it is dependent on metering of the boost signal to control the vanes.
Changes in air density can easily over-spin the thing.

 

I can imagine that it would be hard to control but I also think that the integration of a waste gate to control spikes would solve this issue.

 

You can't integrate a wastegate. That is the problem.
The vanes are controlled with a calibrated actuator inside the turbo. There is no traditional exhaust bypass port.

 

^^Dude! What is up with that vile avitar! Is this how you plan on keeping the kids from stealing from your avatar cookie jar?

 

When I first saw the variable vane turbo on the new 911T I immediately thought that would be a great match for the rotary. I'm assuming they are using nickel alloys in the turbine section to deal with the heat.

MM what are your thoughts on how Porsche is dealing with the overspin question?

 

so if we have so much heat, why hasn't the car-b-que become more popular?

 

I was thinking the same thing, I still think you could install an external waste gate separate from the turbo to control this but that type of redundancy seems counterproductive. At this point I just don't understand the variable sufficiently to suggest a solution.

MM can you give more details on your Miata set up and what would go wrong and when. You seem to have the most experience here so your the go to guy.

 

search the news for the guy that caused his car to catch on fire when tried to heat up his lunch