The damage produced by
fluctuations in oil pressure is cumulative. Every time
the hydrodynamic wedge of oil between the crankshaft
journal and the bearing breaks down, there is
metal-to-metal contact. It may last only an instant, but
that is enough time to start microwelding the two
surfaces. By the time you see the needle on the oil
pressure gauge fall, the damage has already begun. If
you tear down the engine every few weeks, this may not
be cause for concern - but if you overhaul your engine
only once a season, any loss of oil pressure is
potentially dangerous.
Connecting rods often take the blame
for oil system problems. I'm skeptical when a racer
tells me that he broke a rod - nine times out of ten,
the real culprit is a spun bearing caused by lack of oil
pressure. If the crankshaft journal is black, the rod
didn't fail first. Broken rods don't spin bearings -
spun bearings break rods. A true rod failure will always
leave the bearing intact - and it's very rare to see
that.
Sometimes good intentions produce
unintended consequences. Suppose you install an oil
cooler or a remote-mounted oil filter to make filter
changes easier. That's a fine idea - but now you have
added several feet of line to the system that must be
filled before the lubrication system is pressurized.
Unless you have installed a check valve in the line, the
oil will drain back into the pan when the engine is shut
off. Now you've created the opportunity for an air lock,
and you have definitely increased the time it takes for
the pump to pressurize the system. If the engine loses
pressure on shutdown, it will now take longer to
recharge the system when you fire the engine.
I should also point out some
precautions if you use a vacuum pump with a wet-sump
system. We've tested vacuum pumps on numerous sportsman
engines, and learned they are definitely worth power,
especially in an engine with a tightly confined
crankcase. The vacuum pump reduces the density of the
air in the |
crankcase, which in
turn reduces the resistance to the rotating assembly.
It's the same principle that allows an airplane to fly
faster at 20,000 feet altitude than at sea level.
Unfortunately, too much vacuum can be
a bad thing with a wet-sump pan. Remember that it is the
pressure in the pan that forces oil into the pickup.
When you reduce the pressure in the crankcase with a
vacuum pump, you also reduce the pressure differential
between the inlet side of the pump and the pan. Normal
atmospheric pressure is approximately 30 inches of
mercury; if you reduce the pressure in the pan to 15
inches, you have only half as much pressure pushing the
oil into the pickup.
On the dyno, we see fluctuations in
oil pressure when the crankcase vacuum approaches 15
inches with a wet-sump system. We use an adjustable air
bleed (essentially a controlled leak) to regulate the
maximum pan vacuum to between 10 and 12 inches. With the
wet-sump system we install on our Super Series bracket
racing big-blocks, we see no fluctuations in oil
pressure at this vacuum.
In the high-tech pursuit of
horsepower, racers sometimes overlook the basics. A
reliable lubrication system is about as basic as it
gets. All the power you gain with a marginal oiling
system is useless if you're smoking the bearings.
As a professional engine builder, I
hate to see parts destroyed needlessly. I would much
rather help racers step up their program to the next
level than see them spend money on fixing broken motors.
That is why I strongly recommend that you play it safe
with the oil system and look for power elsewhere. |
