Dunno about oil vapours and octane, but the later positive crankcase
ventilation is much better at keeping condensation out of the engine
innards, and the system that ported the carbs direct to the tappet chest
cover was much better than the PCV valve on the inlet manifold. If you
don't have a charcoal canister connected then block off any port on the back
of the rocker cover and use a vented oil filler cap. Open pipes on the
engine will suck air in, together with whatever is suspended in the air, as
the engine cools. Very early MGBs didn't have positive ventilation and used
a open 'draft tube' down from the tappet cover or front cover, and a hose
from the front of the rocker cover to the dirty side of the front air
cleaner. It was a bit hit and miss as to which way any ventilation flowed,
if at all.
Runon is easily cured, if you get preignition that implies hot-spots in the
cylinder head, and pinking too much advance for the fuel. But I suppose if
you were determined to keep the timing where it was, and not porting the
small amount of oil vapour from a sound engine made the difference, then you
might be desperate enough.
PaulH.
----- Original Message -----
From: "Rick Lindsay" <rolindsay@stoolhead.com>
To: "Dennis Luther" <DennisLuther@PrimHall.com>; <mgs@autox.team.net>
Sent: Friday, January 16, 2004 6:26 PM
Subject: Re: Carb Swap Success
> > Here's a question: Are there any good
> > reasons for not running the crank case breather
> > line tee-d into the carb ports?
>
> Dennis, just plug off the line(s) on the manifold,
> etc., and vent the crankcase fumes via a hose,
> down under the car somewhere. The crankcase does
> need to be ventilated but you don't want that
> oil vapor in your intake mixture. Oil vapor
> effectively LOWERS the effective octane value of
> your fuel promoting preignition, knock and run-on.
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