Must Know Facts to Drill -- (Know this)

What is the stoichiometric ratio for gasoline engines?

14.7 to 1.

14.7 to 1 — what is this ratio, and which way round?

The stoichiometric air-fuel ratio: 14.7 parts AIR to 1 part FUEL.

Stoichiometric ratio: ____ parts air to 1 part fuel.

14.7

Which is the larger share in the stoichiometric ratio, air or fuel?

Air, by far — 14.7 parts air to just 1 part fuel.

What does hitting the stoichiometric ratio achieve?

Complete combustion — all the fuel burns with no excess oxygen or fuel left over.

A mixture is 12 to 1. Is that lean or rich?

Rich — less air than 14.7 to 1 means excess fuel.

A mixture is 17 to 1. Is that lean or rich?

Lean — more air than 14.7 to 1 means excess oxygen.

Lean mixture: more of what?

More AIR than the stoichiometric ratio — excess oxygen.

Rich mixture: more of what?

More FUEL than the stoichiometric ratio — less air.

Which mixture has excess oxygen?

Lean.

Which mixture has excess fuel?

Rich.

Which mixture improves fuel efficiency but risks engine knocking?

Lean — it burns hotter.

Which mixture gives more power when accelerating but fouls spark plugs?

Rich.

Fill in the blanks: Lean = more ____. Rich = more ____.

Lean = more air. Rich = more fuel.

What is the common firing order for an inline-4?

1-3-4-2.

What is the typical firing order for an inline-6?

1-5-3-6-2-4.

Which engine has the firing order 1-3-4-2?

The inline-4.

Which engine has the firing order 1-5-3-6-2-4?

The inline-6.

Inline-4 firing order: 1 - ____ - 4 - 2

3

Inline-6 firing order: 1 - 5 - ____ - 6 - 2 - 4

3

Name two common V8 firing orders.

1-8-4-3-6-5-7-2 and 1-3-7-2-6-5-4-8.

Name two common V6 firing orders.

1-2-3-4-5-6 and 1-4-2-5-3-6.

Why does firing order matter?

It distributes the load evenly across the engine and affects balance, smoothness, vibration and performance.

Where would you find an engine's firing order written down?

Stamped or engraved on the engine block, cylinder head or intake manifold.

Name the four strokes in order.

Intake, compression, combustion (power), exhaust.

Which stroke is first?

Intake.

Which stroke comes after compression?

Combustion, also called the power stroke.

Which stroke is last?

Exhaust.

Which stroke is the only one that produces power?

The third — combustion (power).

Four strokes: intake, ____, combustion, exhaust.

Compression

Four strokes: intake, compression, ____, exhaust.

Combustion (also called power)

In which two strokes is the piston moving DOWN?

Intake and combustion (power).

In which two strokes is the piston moving UP?

Compression and exhaust.

In which strokes are both valves shut?

Compression and combustion.

In an SAE oil rating, what does a LOWER number mean?

Thinner oil.

In an SAE oil rating, what does a HIGHER number mean?

Thicker oil.

Which is thinner at low temperatures, SAE 5W-30 or SAE 10W-30?

SAE 5W-30.

How do SAE 5W-30 and SAE 10W-30 compare at high temperatures?

They have the same viscosity — the 30 is the same in both.

What is viscosity?

The oil's resistance to flow at a certain temperature.

Who created the oil viscosity grading system?

The Society of Automotive Engineers (SAE).

Fill in the blank: lower SAE number = ____ oil.

Thinner

OHV — what does it stand for, and where is the camshaft?

Overhead valve — the camshaft is in the ENGINE BLOCK.

OHC — what does it stand for, and where is the camshaft?

Overhead cam — the camshaft is in the CYLINDER HEAD.

Which design uses pushrods to reach the valves?

OHV — the cam is down in the block, so pushrods carry the motion up.

Which design operates the valves directly?

OHC — the cam sits right on top of them in the head.

Which is more efficient and makes more power, OHV or OHC?

OHC.

Cam in the block = ____ . Cam in the head = ____ .

Cam in the block = OHV. Cam in the head = OHC.

What does SOHC mean?

Single overhead cam — one camshaft operates all the valves.

What does DOHC mean?

Double overhead cam — two camshafts, one for the intake valves and one for the exhaust valves.

Which arrangement is found in high-performance engines, SOHC or DOHC?

DOHC — better valve control and higher revving capability.