Alan,

I’ve read the posts in response to your original post.  I’ve also reviewed your original and you don’t say whether or not you are normally aspirated.  Regardless, some of the answers you received conflict with my real life experience so I’ll recount it for you and then retire; I don’t intend to get trapped in endless conjecturing.

I fly a L IVP with a TSIO 550 B2B engine.  It is set up with a low boost, high boost and a push button prime, like one of your responders.  Low boost is always used above 10,000 feet.  On two occasions I forgot the low boost and encountered rough running and then engine surges at about 18,000 to 20,000 feet.  Turning low boost on immediately corrected the problem.

About five years ago my engine quit at 400 feet, immediately after takeoff from Port Columbus, OH, westbound over the city.  No time to think.  I turned high boost on, IAW my understanding of the engine’s needs (thanks, Charlie Kohler) and it immediately recovered.  I climbed out in disbelief of what happened, stayed within easy gliding range of a recovery airport and leveled off at 10,000 feet.  The engine was running perfectly. I then turned the high boost off to see what would happen so I would have a more complete picture for the mechanic.  It instantly quit again.  For the remainder of the flight it ran normally on high boost, even at idle in the high, emergency pattern I used for landing.  It ran normally taxiing in.  The engine shop quickly found that the engine driven fuel pump had suffered a catastrophic failure.

IMHO, the high boost pump worked as designed.  Good luck on your project.

Carl La Rue

L IVP 1560 hrs.