oil control

David Doddek pantera at pobox.com
Tue Jul 16 03:51:06 GMT 1996


Perhaps I can be of some help.  I have twin turboed a 351C in the back of a
Pantera and had my share of problems.  The other replies are right, 90 psi
is too high for both the turbos and the engine.  60 psi is a lot better.
You can change your relief spring on your oil pump with one for lower
pressure and still retain the high volume pump.  Try a spring from a stock
pump, just make sure that it is for the same length of hole in the releif
passage.  You may also be able to get a set of various springs from the
manufacture of your pump.  Another thing that can be done is add a
restriction orfice in the oil lines to the turbo.  About a .040" hole is
usually adequate.  Turbos actually do not need a lot of oil, they just NEED
oil and ALL the time.  The return line is the most critical.  It must be
LARGE.  I have a 3/4" tube leading from the turbos to below the area of high
heat and then a 3/4" hose directly to the TOP of th oil pan.  The return
lines must not be allowed to have ANY back pressure.  Even high cranck case
pressure may cause the turbos to leak oil.  Return lines must empty above
the oil level and not have any low areas that will collect oil and block off
the natural flow of the return oil.  The large diameter of the lines is
necessary because when oil passes through a bearing with a shaft spinning at
up to 100,000 rpm the oil tends to turn into something that resembles whip
cream.  Whip cream does not flow well in a pipe.  If the pipe is too small
then pressure will be built up in the turbo and get pushed out the seals.
There are two types of seals in a turbo, a dynamic and passive seal.  The
dynamic seal is simply a disk that slings the oil away from the shaft before
it gets to a section of little ridges to try and hold the oil back.  There
is actually no real physical pressure seal.  The passive seal consists of a
carbon disk that has a very close fit to a mating surface to seal out the
oil.  The dynamic seal is not suitable for a setup where the throttle body
is upstream of the turbo.  The vaccuume in the intake will draw oil out of
the turbo into the intake.  It will also allow gas to get into the turbo
bearings and make them wear out fast.  The passive carbon seal is better,
but costs more.  Remember, the shaft of a turbo has bearings that "float"
and the shaft may move around to a small extent.  They are designed to have
slop in the shaft bearings.  The oil takes up the gap.  This is the only way
that bearings can have low resistance and live at 100,000 rpm.  I hope this
is of some help.  I had a few of these problems, and had to learn the hard way.

David J. Doddek                                          |pantera at pobox.com
Owner SGD Electronics & Development Engr for Caterpillar |h 309 685-7965
Formula SAE Team Sidewinder 94-95                        |w 309 578-2931
89 T-bird SC,  69 Fairlane w/SGD EFI                     |fx 217 428-4686
74 Pantera w/Electromotive Tec-II Twin turbos and Nitros |
Hey, If you are going to go fast, go REEEAAL FAST.       |




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