Actually I have an STCd system to do just that, the SVS system from SafeFlight. It has a manifold with check valves functionally similar to the one you picture except there is only one inlet from the instruments. One outlet goes to my dual venturis, and the other to the base of the 1-3-5 intake manifold through a manual shutoff valve. I had the manifold modified with a 3/8” NPT pipe boss, as the existing 1/8 primer boss is way too small for the required flow. The system is intended as a backup vacuum source, so there is also a required vacuum switch to drive a light warning of loss of the primary source.n2582d wrote:If approval wasn’t an issue, I’d try routing one side to the engine manifold, and the other side to your venturis. That would permit gyros to be spun up as you taxi out. A problem with this idea might be that tapping into the intake manifold would cause those three cylinders to run leaner, similar to having a vacuum leak there. A moot point as there is no approval for such a modification.
The boss I had installed on the right intake manifold replaces the primer boss near where the manifold attaches to the sump, so it doesn’t seem to inordinately affect the cylinders on one side over the other. I do get about a 100 rpm rise at idle due to the additional airflow with the system on, but the engine maintains its normal smoothness. I leave the system on most of the time so I have he gyros powered on the ground. When the throttle opens on takeoff, the manifold vacuum goes away, but the venturis quickly take over, so im never really without vacuum. About the only time I shut it off is sometimes when I’m a little high on final to get the engine down to a true idle.
I found an 
