Also bear in mind Achima's 1800 l/min calculation....I don't know what the required airflow through the gyro instruments is, but I would guess it is waaay less than that....ie impact on mixture is likely insignificant....do you know the flow rate required?
If you introduce extra air into one cylinder, you will make it richer
Think about that statement again 
Yes; wrong way round
But that is even worse. The (much more) typical pilot flying ROP is going to get a big increase in CHT.
The vacuum takeoff ought to go nearer the air intake, but there probably isn't anywhere neat to drill the hole, and the air filter itself drops only around 0.2-0.5 inches of MP so you won't get much vacuum right after it. (I know this because a few years ago a bunch of TB owners bought some K&N filters but even after sorting out some bad fitting (the STC failed to take into account different metalwork on different S/N airframes) there was no reported MP improvement).
The take-off would need to be engine side of the throttle to be of any use
The take-off would need to be engine side of the throttle to be of any use
Exactly, but there is no way to do that except a blatent hack involving the drilling of a big hole into the side of the fuel servo (or carburettor) because this item is screwed directly onto the bottom of the engine.
Maybe there is a point on the sump casting where one could drill the hole....
Hello!
I don't think the vacuum comes from the induction manifold itself but it is "made" from the pressurised air behind the turbocharger by an ejector pump. Just as vacuum on turbine engines is made from hot bleed air that way (sounds strange, but that's the way it is.). Most turbine driven aircraft have all-electrical instruments, but vacuum is still required by pressurisation controllers and to suck the air out of deice boots.
max
NB: And looking at the plumbing in the photo, the air is bled so close from the manifold that it will hardly have an influence on that rear cylinder.
Peter - I built a similar bench vacuum system but used an electric drill to power it. On a Saratoga I've seen a separate vacuum pump driven by an electric motor; interestingly, if this becomes inop does in preclude IFR flight?
... if this becomes inop does in preclude IFR flight
I have never seen it stated anywhere that a dual vacuum system is required for IFR flight.
From the Precise Flight installation manual online:
TURBOCHARGED ENGINE OPERATION All turbocharged, single engine aircraft powerplants have vacuum in the intake manifold until the turbocharger begins to supply pressurized air to the engine. When the turbocharger is operating engine intake manifold pressure will exceed ambient air pressure. The engine manifold is pressurized. An example would be the Mooney 231. The Mooney 231 is equipped with a turbocharger and when taking off utilizing a power setting of 40 in Hg., the intake manifold is pressurized to provide additional power to the engine. Once the aircraft is at cruise speed and power at 8000 ft to 10,000 ft altitude the power setting is reduced to 27 in. Hg. and the engine intake manifold is pressurized by the turbocharger. The Precise Flight Standby Vacuum System relies on the difference between the outside ambient air pressure and the intake manifold pressure, power settings on a turbocharged engine will have to be reduced to allow proper Standby Vacuum System operation Once a turbocharged aircraft is at altitude, and has a vacuum pump failure, a slow and safe descent to landing, using low power settings, will be necessary to effectively operate the SVS system. In the Mooney 231 you can cruise with 18.5 in. Hg. at 8,000 ft. MSL, which will provide the required vacuum to maintain primary gyro instruments. On final approach you will have the best possible vacuum. The aircraft engine, turbocharged or not, is developing more vacuum than the primary gyro instruments need and the vacuum regulator will keep the system within limits.
On a Saratoga I've seen a separate vacuum pump driven by an electric motor
This was a popular fit at one time
Damn heavy!
They used the vac pump inlet air to cool the motor.
I have never seen it stated anywhere that a dual vacuum system is required for IFR flight.
I recall (vaguely) that the above backup system had something like a 10 year life limit, so it had to be overhauled or thrown out at 10 years even if it had been never or almost never used. I also don't see how it could be mandatory for IFR unless the airframe TCDS had it on it, saying that.
