From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: max vacuum saves fuel
Date: Mon, 21 May 2001 19:02:52 -0400

Dick Campagna wrote:
>
> David Martin <dmartin@iastate.edu> wrote in article
> <Xns90A75FD53EC16dmartinnewartscom@24.179.208.88>...
> (snip)> Accelerating more slowly to a slightly higher cruising speed was
> the basic
> > source of my increased fuel efficiency.
>
> A government (?) study I read recently said that full- or
> almost-full-throttle acceleration through the gears, combined with low
> shift points . . . gives the best fuel mileage when accelerating up to
> cruising speed.  The full- or almost-full-throttle part is important, since
> it opens up the throttle butterfly, thereby reducing restriction.

This is true, at least if you have EFI. May or may not be true with
a carb, depending on the WOT enrichment scheme.

Another method along the same lines of reducing windage and pumping
losses if your engine will take it is to pull a vacuum on the
crankcase.  This both reduces the density of the air the crank and
rods move through AND it reduces the air pressure under the
pistons.  This is an old racer's trick that really works.  If your
engine can take it.  Issues include intake and rocker covers that
suck in from the vac and crank seals that either suck in or whistle
like a banshee.

If the engine will take it, the configuration is simple.  Simply
replace the PVC valve with a check valve allowing flow toward the
intake and another check valve on the valve cover vent allowing flow
only outward toward the air cleaner.  This scheme uses the engine
vacuum to pump the crankcase down while providing a path outward in
the event of excessive blowby.

John

From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: max vacuum saves fuel
Date: Tue, 22 May 2001 02:07:44 -0400

David Martin wrote:
>
> >
> >Another method along the same lines of reducing windage and pumping
> >losses if your engine will take it is to pull a vacuum on the
> >crankcase.
>
> Will a ford 460 "take it?"

No idea.  You'll have to find out the same way I found out about
Datsun Z (won't), Mopar 318 (will, with a rubber and not cork oil
galley gasket) or chevy 350 (my particular version will) and Toyota
Camry (will) engines - try it. Worst thing you have to lose is to
replace a gasket or a seal.

John