Why does the 4KQ need a separate vacuum pump - next question.

[Bill Phelps]

Thanks to All for the replies.

So if you were turbo charging a 4KQ and were using the MC head, what would
you do? Rely on a big vacuum reservoir, check valve, and off boost brake
application? Machine the head to accept the vacuum pump? I'm not going to
swap brake boosters... No bombs in my car thanks...

Just wondering what those of you who have done this conversion have ended up
doing...

Granted, I try to keep my Walter Rohl-style left-foot braking to minimum....
except in the snow :)

Bill


> -----Original Message-----
> From:	Huw Powell [SMTP:human747 at attbi.com]
> Sent:	Tuesday, September 24, 2002 12:56 AM
> To:	Bill Phelps
> Cc:	quattro
> Subject:	Re: Why does the 4KQ need a separate vacuum pump?
>
>
> > > 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/