[DeTomaso] vacuum line schematics

[Doug Braun]

Since the PCV system is a continuous calibrated leak, it will lean out the
mixture if not compensated for by jetting and idle mixture control.  It's
best not to connect it to the manifold ports that are at the top front and
top rear of our dual plane manifolds because these points only feed two of
the eight cylinders which will lean those two cylinders out.  It's best to
take the PCV vacuum from a point that is common to both intake banks which
is only possible at the carb baseplate.  Most all Holleys have such a port
and I believe there are carb spacers available that provide a PCV vacuum
port.  You can also make one yourself by drilling a phenolic carb spacer to
access both banks equally and adding a fitting to its front or rear.  This
way the leak caused by the PCV vacuum draw will automatically get
compensated for when you properly set your idle mixture screws and pick your
main jet sizes.

BTW, connecting the power brake vacuum to one of the manifold ports is OK
because the power brake booster only draws it's greatest vacuum while
braking and it's need for vacuum quickly drops to zero as you get back on
the gas after a stop (that is unless your booster has a leak which will
cause the two cylinder lean-out problem I mentioned above).

Doug Braun
blue 73L #5505

-----Original Message-----
From: detomaso-bounces at realbig.com
[mailto:detomaso-bounces at realbig.com]On Behalf Of MikeLDrew at aol.com
Sent: Saturday, July 21, 2007 11:12 PM
To: charlesbuthala at yahoo.com; detomaso at realbig.com
Subject: Re: [DeTomaso] vacuum line schematics


In a message dated 7/21/07 3:55:40 PM, charlesbuthala at yahoo.com writes:


> When I purchased my car the vacuum lines for the brakes went from the
> carburetor port, to a "T".  One end of the "T" went to the brakes and the
other
> went to the valve cover for cylinders 5-8.  I was wondering what other
cars had
> as a routing schematic.  I get some confused looks when mechanics look at
> the set up.  Is this correct or is there a better way to route the lines
so
> that the system works correctly.
>

The 'correct' setup is as follows:

Vacuum port on intake manifold (on the rear on the stock intake, either end
on most aftermarket intakes) is used for brake vacuum.   PCV vacuum goes
from
PCV valve on left valve cover, to the port at the base of the (aftermarket)
carburetor.   Crankcase draws air from the base of the air cleaner through
the
fitting on the right-side valve cover.

I don't know if it's a 'bad thing' to use a "T" to get vacuum for both the
PCV and the power brakes from a single source.

Mike