[ThePHNX]

Terrific Info.
The 3000~3200 comes quite close to that `magic' 75% setting.
BTW: spent some time thinking about it and have to disagree with you on the vacuum gauge. Manifold pressure and vacuum tell a great deal about load and efficiency on normally aspirated Internal Combustion Engines. Suspect you have used a shop gauge to diagnose engines, the common panel gauges are colour coded to show most efficient, moderate overloading and heavy overloading. A few of the high performance cars I've had came with vacuum gauges straight from the factory - think it was a mercedes that described it as a better shift indicator than simple RPM. Several machines have had `shift lights' that were the vacuum equivalent of an idiot light. The value of the gauge is somewhat diminished by the skill of the user. In hands like yours, I'll bet you can spot a burnt or sticking valve, ot other combustion problems with one.

You are right that it is not an instrument for constant reference, but I can see smoothing out acceleration and getting up on step by keeping it `in the green'.

Am thinking that if we do install one it might just as well go on the engine housing facing the console rather than run tubing hither and yon. Is there a vacuum sampling port on the Merc's?

Back to your excellent info on instrumentation. As you pointed out previously a fuel flow reading that is computed rather than actually measured is less desirable than a true flow measurement. What units in your experience actually give true readings rather than estimated?

Did you also ever see my question as to instrument calibration services?

Thanks, HBH