Re: 5000 brake booster (servo)

[rdh@genrad.com (Robert D. Houk)]

   >> Before I rebuilt mine, I considered getting
   >> an ELECTRICAL 12 VOLT PUMP, with a cutoff switch and a pressure
   >> accumulator. It would take the constant one or two horsepower
   >> load off the engine and put it onto the battery. This pump would
   ...
   >This is not a bad idea, tho you may find that the pump is hard to
   >mount, and it may end up running most of the time.  Also, keep in mind
   ...
   1. One large electrically driven pump, 2000 psi, and one fairly
   large ( three or four times the present one ) pressure accumulator.
   The pressure accumulator would have a pressure switch on it which
   ...
   Anyway, its food for thought, the best benefit may come from
   removing the constant one or two horsepower load from the
   driveshaft belt, and replacing it with an intermittant load
   on the electrical system. I'd hesitate to put a larger
   number on the constant horsepower draw of the present system,
   but take your best guess.
   ...
   ( Needless to say, I've studied the pump and the design of the
   hydraulic system  at considerable length, during my re-building
   experiment ).

>From my experiences with Audi Electricals, I would be very *very VERY *VERY*
hesitant to put any more load on the factory electrics, especially one that
rates in the horsepower units (as I recall, dimly, 1 HP = 746 WATTs which
will draw around **60** amps at 12 volts! Thats 100% efficiency, so factor
in electric motor losage and you are talking three digits (**100** amps!)
as the starting point for your pump. Just lugging enough heavy-gauge wire
around to hook up your pump may well cost you more hp than you save by off-
loading the engine...(not to mention the extra alternator or two needed to
drive the extra electrical load! or coupla hundred ft**2 of solar panel!).

I would guess a much better tradeoff would be simply (Audi? Simple? Ha!)
putting a larger pulley on the pump to "gear it down", as it were, to pro-
vide a smaller percentage load on the engine. (By default, the system is
providing enough "assist" so that grandma can parallel park with just her
little pinky on the wheel, constantly pumping the brakes; so I would think
that you have "lots of room" to reduce the engine load . . .)

						-RDH