Why does the 4KQ need a separate vacuum pump?

[Huw Powell]

> > Just wondering why the cam-driven pump is needed for the brake
> > booster....It's the first one I have seen on a car..

"needed" is a relative term.

In "normal" driving it will never be noticed, as the engine at idle
makes plenty of vacuum to keep the power brakes assisted nicely.  The 83
and earlier cars (except urq, with its hydraulic system) have no such
off-idle back up, including the 5000 turbo.

If you try driving one without a pump at 3-4k rpm and apply the brakes
several times, the assist will vanish.

It's kind of a racing heritage thing, I think.  They want their
customers to be able to left foot brake while revving the engine...

--
Huw Powell

http://www.humanspeakers.com/

http://www.humanthoughts.org/