Date: Thu, 10 Jan 2008 10:37:34 -0500
Reply-To: Mike S <mikes@FLATSURFACE.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mike S <mikes@FLATSURFACE.COM>
Subject: Re: oil pump blueprinting question
In-Reply-To: <A817922C9DAF504580C0D892C343677603795311@GNBEX01.gnb.ca>
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At 08:21 AM 1/10/2008, Giasson, Pascal (DNR/MRN) wrote...
>I have my old OE oil pump out and I noticed that the pump outlet
>port/hole is smaller that the receiving hole in the case...If I
>enlarge the outlet port on the pump then I would guess that the oil
>pressure inside the pump might be reduced, but what will that do to
>the oil presser elsewhere. If port matching is ideal then why did VW
>not do this in the first place?
To "blueprint" is to exactly match factory specifications, correcting
for the allowed tolerances (i.e. if the factory spec is a 12mm +- 1mm
hole, you would want an exact 12mm hole). Also, gear clearances,
endplay, etc. Having said that, it's common for people to refer to
performance modifications as "blueprinting." Here's what Bob Hoover has
to say on the matter:
http://groups.google.com/group/rec.autos.makers.vw.aircooled/msg/20cb7f6f86953f1b
Suction ports will normally be larger than pressure ports. You can only
have a suction differential equal to the crankcase pressure, which is
slightly more than atmospheric, so a bit over 1 bar (15-16 psi). The
pressure side can be arbitrarily high, but VW considers 0.9 bar an
absolute minimum at 2K RPM. It should normally be significantly higher.
The greater the differential, the smaller the hole required to support
the same flow.
Changing the outlet size should have little effect on the oil pressure
on a stock engine, which is determined almost entirely by the delivery
rate of the pump (volume per revolution), viscosity of the oil, and the
various clearances in the engine.
If you want more oiling, look for a high volume pump, not bigger ports.
But be careful, the stock pump has sufficient capacity and high volume
pumps can create so much pressure that the pressure reliefs can't
properly do their job - it can cause the oil cooler pressure relief
valve to stay open, causing less cooling. You might also blow oil
galley plugs or oil filters.
Overall, for a stock engine, I don't think port size matters, nor do
you need a larger pump. The only "blueprinting" needed is checking oil
pump clearances (probably need to use plastigage for checking endplay
on a T4 pump).
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