Question 1

Which dynamometer design deals with higher loads more effectively: water brake or eddy current?

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Question 2

The work efforts needed to move air into and out of the cylinder are called _________ losses.

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Question 3

Technician A says that it is normal for the piston to remain stationary at TDC for a few degrees of crankshaft rotation. Technician B says that if the intake valve is open more at TDC than the exhaust valve, the cam is retarded. Who is right?

Accepted Answer

Technician A is correct because during the four-stroke cycle, the piston does indeed pause momentarily at Top Dead Center (TDC) due to the crankshaft and connecting rod mechanics. This is a normal part of the engine's operation. Technician B is incorrect because the relative opening of the intake and exhaust valves at TDC does not directly indicate cam timing (advanced or retarded); it depends on the camshaft design and the engine's valve timing setup.

Question 4

What is the term that describes the part of the power stroke between the time the exhaust valve opens and the piston arrives at BDC?

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Question 5

High rpm power is improved by _____ cam timing.

Accepted Answer

Retarded cam timing improves high rpm power by delaying the closing of the intake valve, allowing more air-fuel mixture to enter the cylinder at higher speeds.

Question 6

Technician A says that the rpm range of the engine is controlled by the point where the intake valve closes. Technician B says that closing the intake valve later in the compression stroke lowers the effective compression ratio. Who is right?

Accepted Answer

The rpm range of an engine is indeed influenced by the point at which the intake valve closes, as it affects the engine's volumetric efficiency at different speeds. Closing the intake valve later in the compression stroke does indeed lower the effective compression ratio because it allows some of the air-fuel mixture to escape back into the intake manifold, reducing the amount of mixture available to be compressed.

Question 7

Both of the following cams have intake and exhaust lobes of identical lift and duration. Which has more overlap, the camshaft with lobe centers at 112° or the camshaft with lobe centers at 114°?

Accepted Answer

The camshaft with lobe centers at 112° has more overlap. Overlap refers to the period during which both the intake and exhaust valves are open at the same time. A smaller lobe separation angle (112° vs. 114°) results in greater overlap because the intake and exhaust lobes are closer together, causing the intake and exhaust valves to be open simultaneously for a longer period.

Question 8

What is the term that describes the camshaft position when the piston is at the top of the intake stroke, the intake valve is beginning to open, and the exhaust valve has not yet finished closing?

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Question 9

What is the name of the one camshaft angle that is measured in camshaft degrees instead of crankshaft degrees?

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Question 10

Camshaft timing readings on OHC engines are taken before/after (choose one) the cylinder head is installed.

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Question 11

The usable horsepower at the crankshaft is known as ____.

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Question 12

A change of 0.001" in valve lash will result in approximately _____° of duration change.

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Question 13

What would be the valve lift with a 1.5:1 rocker arm ratio and 0.300" of lobe lift?

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Question 14

On the intake stroke, a big gulp of air happens when the piston reaches its maximum velocity at ____° of rod angle.

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Question 15

To improve idle quality on longer duration cams, _____ lobe centers are used.

Accepted Answer

Wider lobe centers are used to improve idle quality on longer duration cams because they reduce overlap, which in turn reduces the amount of unburned fuel and air exiting the exhaust. This leads to a smoother idle.

Question 16

Which engine can achieve higher crankshaft rpm, one with a short stroke or one with a longer stroke?

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Question 17

Closing the intake/exhaust [choose one] valve too soon can increase detonation.

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Question 18

When inertia from exhaust gas exiting the cylinder sucks out even more exhaust, this is called ___________.

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Question 19

When a cam lobe is ground differently on its opening and closing sides, this is known as a(n) _____ cam lobe.

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Question 20

The timing of the camshaft events is listed in camshaft/crankshaft (choose one) degrees.

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Quiz 19: Producing Power: Valve Timing, Power and Torque Measurement