To the extent that's true, it's only for the period of high acceleration (I know this intimately since my first vehicle was a 1967 Kaiser Jeep CJ-5 with vacuum

To the extent that's true, it's only for the period of high acceleration (I know this intimately since my first vehicle was a 1967 Kaiser Jeep CJ-5 with vacuum powered windshield wipers). Once the new engine speed is achieved, that vacuum sure ought to come back (weaseling because I don't remember checking for this while at sustained high RPMs).