Hi Jack,
Good use of an old trick, Drag racers have been using this method for years.
For a V-8 the common method is to use 2 backfire valves, one per header bank and
vent each valve cover to it's respective header. sometimes a cover over tube is
also used between the valve covers breathers to equalize pressure. I know a
couple of after-market company's ( Mr.. Gasket, Moroso, etc..) used to market
complete kits, fittings, anti-backfire valves hoses etc.. all together.
Hope this might help anyone else who is thinking about doing it.
Just insure that there is also a source of clean ( filtered) air entering the
crankcase other wise you will suck the oil right out of the engine! Don't laugh
I saw it happen one night at the old Fremont, California drag strip! Yes I do
remember them!! lot of blue exhaust smoke! ( before it broke!)
Steve
1963, Jaguar MKII 3.8,& 72 XJ-6 (I grew up!)
______________________________ Reply Separator _________________________________
Subject: Re: A Series engine breathing
Author: "Jack W. Drews" <vinttr4@FORBIN.COM> at SMTPLINK-clavin
Date: 11/6/96 8:26 PM
Here's an alternative means of venting the interior of the engine. I am
using this on my TR4 vintage racer engine as are two others in my circle
of friends. I make no claims for HP increase, etc since the only way
we'd know is by dyno measurements.
Basically the method is to vent it to the exhaust system. Weld a small
diameter - in my case 3/8" - tube into the collector pipe of the header
so it protrudes about halfway into the exhaust stream at at a 45 degree
angle. The end of this tube inside the header should be cut off also at
a 45 degree angle so that the opening is actually at a 90 degree angle
to the exhaust flow. To the end of the tube sticking out of the header,
braze a pipe fitting so you can screw onto it an anti-backfire valve
from a Chevy available from NAPA, for example. Then run a rubber hose
from a vent on the engine to the anti-backfire valve. On my engine, I
used the vent in the rocker cover.
In my area, circle track racers and tractor pullers use this technique.
They claim better ring sealing due to the slight vacuum pulled on the
engine interior due to the suction created by the flow of the exhaust
gas. They caution us to use the anti-backfire valve so in case of
backfire you don't blow the pan off, which has been done on Chevy V8's
On my car it worked successfully, yielding an almost leak-free engine,
no sign of performance deterioration, but no big boot in the pants
increase either.
I expect this approach to be rather controversial and will enjoy seeing
the responses to this one.
Jack W. Drews (A squealing tire is a happy tire - we Iowa guys know
about that squealing stuff)
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