Annular boosters on a Tunnel Ram

Another thought about your dyno test, is what Mattax posted in the vacuum advance myth section, maybe it needs to be a higher load during your test?? Guessing here. Idle is surprisingly high load, and before emissions concerns, fairly rich. The engine is producing very little torque at 500 or even 600 rpm. A percentage of that goes to overcoming friction. So best to think of it as a high load, somewhat rich and dense situation.