Seriously close to "not at all".
Your instruments want to see vacuum of about five inches Hg to operate.
I'm guessing they'll still function OK down to four inches Hg.
That means your manifold pressure would need to stay at least 4 inches
below ambient atmospheric pressure to keep your gyros up to speed.
That sacrifices a lot of climb power, for sure.
---JRC---

"Andrew Gideon" wrote in message =
online.com...
=20
One of our club airplanes has something like this. But someone told =
me that=20
it works least well under full throttle...which means down low =
executing a=20
missed approach.
=20
Was I told correctly? How serious is "least well"?
=20
- Andrew