Dave,
On the modified we run three large scavenge stages (#12) two in the pan
and one split to both rocker covers. We scavenge the rocker covers because
we run a lot of oil up there to keep all the hemi-Chevy pushrod motion lubed
and to cool the valve springs. The ballooning I referred to was indeed from
burning pistons, something we should avoid but don't always. I was wrong
about the size of the vent lines though they are #16 lines and so far have
been big enough. The amount of pressure the blower can put into the pan when
the rings/pistons go away is awesome alright and we just decided that trying
to pull a vacuum in the pan was just too expensive re replacing dry sump
pans.
What I was asking about is what I ought to do for the 181 cu in four
cyl that I am building for my street roadster. It will be unblown on gas and
SHOULD not have the problems with blowby and fire in the pan that we have
with the modified. The pump I have is the latest Barnes deal with two large
scavenge stages and is their standard midget setup which they recommended as
did Joe Fontanna. I hadn't got around to calling them with my questions yet
but I will. The list is a convenient source and I like to get all the advice
I can and try and sort it out, comes from my years as an apprentice tool and
die maker.
Thanks for the help, Jim
----- Original Message -----
From: Dave Dahlgren <ddahlgren@snet.net>
To: Jim Dincau <jdincau@qnet.com>
Cc: Land Speed List <land-speed@autox.team.net>
Sent: Monday, January 15, 2001 1:44 PM
Subject: Re: Breathers
> Not even close....4 is a lot closer...4 large stages that
> is...they come in different widths depending on what pump
> you use. Might want to call whoever made it for sizing
> advice but I bet they opt for 4 large scavenge stages..
> Might want to put some filler in the block too if this
> 'expansion' is not caused by an 'explosion'.. burned piston
> or disappearing rings. i would put 3 in the pan and 1 in the
> valley then vent the tank with a -20 to the tank.. If you
> really think about the pressure you are playing with a -12
> is a bit on the small side. I would run -16 scavenge if need
> be too..
> Dave Dahlgren
>
> Jim Dincau wrote:
> >
> > Hi all, another poll,
> > On the modified (blown/fuel), because of past experience with
torching
> > pistons, we run two number 12 lines direct to atmosphere from the valve
> > covers. I know this isn't the most environmentally friendly thing to do
but
> > we have ballooned oil pans and catch tanks before and they are expensive
to
> > replace.
> > On unblown gas dry sump engine, will a two scavenge stage pump
pull
> > enough vacuum to allow venting the tank only? If additional vents are
> > required is the rocker can or the tappet chamber a better place to vent?
> > Jim in Palmdale where it has actually rained an inch this month
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