[s-cars] Bypass valves - Which one?

[Kaklikian, Gary]

My other car ('89 944 turbo) uses an excessive amount of oil, although I run only only 16psig boost (18-20psig is max to run safely.)  Although I'm barely within factory specs for "normal driving" - up to 1.5 liter per 1000km, on the track it's a different story - up to 1/2qt per 20min session. And this with a new Garrett T04E, which may be part of the problem, though oil consumption was the same with the old K27.  The car runs great, but I'm sure all the oil is reducing intercooler efficiency and fouling the combustion charge.

Anyway, the oil filler on these engines has a rudimentary air/oil separator - the air (oily vapors) are routed to the turbo inlet, the oil drains down to a plenum in the lh motor mount (yes, the motor mount!), which then drains to the oil pan. The turbo sits atop this motor mount, and drains its oil through the same plenum.

So, I though I'd experiment by routing the "air" line from the separator to a catch can instead of the turbo inlet.  Well, little oil was collected in the can, but the oil dipstick repeatedly blew out on the track (again at only 16psig boost). So, I became wary of blown cam seals, etc and removed the catch can.  The vacuum created by the compressor was obviously helping relieve crankcase pressure. 

At this point I'm not sure whether the problem is high crankcase pressure, excessive blowby from worn piston rings, the turbo seals, or an inherent flaw in the design of the oil drainage from the air/oil separator and turbo on this particular motor, all except the last of which would be applicable to the Audi 20vt motor as well.

But I would avoid routing the crankcase vent to a catch can vented to the atmosphere without some other means of scavenging the crankcase pressure.  My next experiment will be to install a homemade oil filler cap with a one-way sump pump check valve to hopefully reduce crankcase pressure, but I'm not convinced this will have much effect on oil consumption.
 


Message: 9
Date: Mon, 08 Dec 2003 20:09:12 +0100
From: Mihnea Cotet <mik at info.fundp.ac.be>
Subject: RE: [s-cars] Bypass valves - Which one?
To: "Trevor Frank" <tfrank at symyx.com>, "Russ Panneton"
	<russ at panneton.name>,	"Joseph Pizzimenti" <pizzoman at yahoo.com>
Cc: QSHIPQ at aol.com, gary.m.lewis2 at BOEING.COM, s-car-list at audifans.com,
	CaptMagu at aol.com
Message-ID: <5.2.1.1.0.20031208193938.0298d5e8 at info.fundp.ac.be>
Content-Type: text/plain; charset="us-ascii"; format=flowed

I agree totally with Trevor on this one, the reason why the crank case oil 
fumes are being recirculated into the intake is because of some silly 
ecologists that have decided it should be so a few dozen years ago. I know 
they weren't that silly but the principle itself is anti-mechanical.

Though, with regards to detonation/pre-ignition, I guess it would take 
$hitloads of oil puking through the breather in order to produce 
detonation, but then it would mean that the engine is so FUBAR that it 
doesn't need to have any performance anymore...

Just my 0.02 Euros,


Mihnea

At 10:16 8/12/2003 -0800, Trevor Frank wrote:

>So I have some data from an oil manufacturer that says that oil in the
>crank case suffers from recirculation of the crank case vent into the
>intake.  In addition to displacing cool clean air, introducing crap like
>burnt and un-burnt hydrocarbons, reducing octane, etc...  Worse
>increasing combustion pressure because of non-compressible in the charge
>air and screwing up your ignition timing, i.e. to much pressure too
>soon, witch could lead to detonation/pre-ignition.  Then to add insult
>to injury also creates blow by that will degrade the oil in all sort of
>bad ways.
>
>Send it into the exhaust with an egr valve on it if you want the benefit
>of negative crank case pressure.  Get a smog pump or purpose made vacuum
>pump to run off the motor.  But on a high hp motor teetering on the end
>of oblivion it is, imho, dangerous to put it back into the intake.
>
>-----Original Message-----
>From: Russ Panneton [mailto:russ at panneton.name]
>Sent: Saturday, December 06, 2003 7:48 AM
>To: Joseph Pizzimenti
>Cc: QSHIPQ at aol.com; CaptMagu at aol.com; mlped at qwest.net; Trevor Frank;
>gary.m.lewis2 at BOEING.COM; s-car-list at audifans.com
>Subject: Re: [s-cars] Bypass valves - Which one?
>
>I thought the main reason to keep oil out of the intact tract was that a
>
>little oil reduces the effective octane rating of the gasoline, leading
o more chance of detonation...


>Joseph Pizzimenti wrote:
>
> >Scott,
> >Not only does it help with combustion, but it also
> >helps keep your intake tract clean and help those
> >Samcos from popping off with all that oil.
> >
> >
>
>
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