Chevy High Performance – October 2019

26 CHEVY HIGH PERFORMANCE II OCTOBER 2019

Preaching Tolerance

pressure, a looser clearance will

reduce flow resistance and lower

the oil pressure. Conversely, tighter

clearances increase resistance to

increase oil pressure.

Oil viscosity contributes to

resistance, with thinner oils reducing

it and thicker oils increasing it.

That’s why it’s more important and

advantageous for performance

engines with tighter bearing

clearances to use thinner oils and vice

versa for looser bearing tolerances

and thicker oils.

Keep in mind, too, that a large

increase in pressure does not equate

with a large increase in oil flow.

Pressure increases exponentially with

flow, so a large increase in pressure

will only net a comparatively small

increase in oil flow.

OIL FLOW IMPORTANCE

Regardless of the clearance, oil

flow through the bearings is critical for

carrying away the heat generated by

friction. When oil flow isn’t sufficient

enough to carry away heat, the oil

will overheat and the thin oil film will

break down quickly, allowing metal-

to-metal contact and quite possibly

catastrophic engine damage or seizure

shortly thereafter.

For even mildly built, street-

performance engines, that means

a high-volume oil pump is a smart

choice, especially when running tighter

bearing clearances and thinner motor

same as a previously higher-viscosity
oil in the same engine.
The consequently lower drag on
the oil pump and piston ring pack that
comes with a lighter oil frees up a few
horsepower, too, and allows for tighter
bearing clearances than would have
been previously recommended.
Now, does that mean you can just
pour 0W30 oil into your vintage 350?
Not necessarily. Although modern oils
offer greater load-carrying capacity,
an original, unrestored engine may
need the thicker oil for other reasons.
But if the engine has been rebuilt with
more precise machining, then yes,
experiment with thinner oils to see
what works the best—just be aware
that you’ll probably see lower oil
pressure as a result.

BEARING CLEARANCE VS.
OIL PRESSURE
Oil pressure is the result of two
things: oil flow volume from the pump
and oil flow resistance in the engine.
Higher pressure comes from greater
resistance, while lower pressure is the
result of less resistance.
When it comes to bearing
clearances and their effect on oil

Oil pressure is affected by flow resistance through
the engine. Tighter bearing clearances increase
resistance, increasing oil pressure; but pressure
isn’t necessarily as important as adequate oil flow
to keep the bearings lubricated.

Oil flow in Chevy

small-block, LS, and

LT engines starts

with the valvetrain

before it feeds the

main bearings.

Later-generation

big-block

(Marks V and VI)

and Chevrolet

Performance’s

LSX blocks feature

priority-main oiling

circuits that feed

the mains first.

Oil flow is critical

to maintaining

the hydrodynamic

wedge between the

journal and bearing.

A high-capacity oil

pump on even mild

performance builds

is, therefore, a

smart and relatively

inexpensive

investment.

Starting with the 2019
model year, all Corvette
models use Mobil 1 ESP
0W40 engine oil; earlier
LT engines use 5W30
oil. These comparatively
thin oils are designed
to reduce friction and
enhance emissions
performance at start-up,
but they’re enabled
by tighter tolerances
throughout the engine.