Interesting to read Bob Hoovers' post Mike.

Thanks!

Neil.

--
Neil Nicholson. 1981 Air Cooled Westfalia - "Jaco"
http://web.mac.com/tubaneil

Engine swap beginings: http://tubaneil.googlepages.com/

On 1/10/08, Mike S <mikes@flatsurface.com> wrote:
> 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).
>