Cylinder Bore Diameter of the engine cylinder Measured across the cylinder, parallel with the top of the block Cylinder bores vary in size, but typically range from 3–4" (75–100 mm)
Piston Stroke Distance the piston moves from top dead center (TDC) to bottom dead center (BDC) Crankshaft journal offset (throw) controls the piston stroke Stroke varies from about 3–4" (75–100 mm)
What happens if the engine is bored? Definition: Boring Material is moved from the cylinder walls and a larger piston is installed Displacement & compression ratio are both increased when bored (AKA “bored out”) How would the displacement of a stock 6 cylinder engine with a bore of 4.000” and a stroke of 3.000” change if it were bored 0.060”? Changing Bore Size
What happens if the engine is stroked? Definition: Stroked Changing the crankshaft offset (installing a new crankshaft) Displacement & compression ratio are both increased when stroked How would the displacement of a stock 6 cylinder engine with a bore of 4.000” and a stroke of 3.000” change if it were stroked 0.125”? Changing Length of Stroke
What happens if the engine is bored & stroked? Changing the crankshaft offset and boring the cylinder How would the displacement of a stock 6 cylinder engine with a bore of 4.000” and a stroke of 3.000” change if it were stroked 0.125” and the bore 0.060”? Change of Bore and Stroke
How to increase engine output How to increase engine output Increase volumetric efficiency Better gas flow Forced induction Altered valve timing Improve engine efficiency Better combustion efficiency Lower internal friction Reduce heat loss Better fuel
Piston Displacement Volume the piston displaces as it travels from BDC to TDC Found by comparing cylinder diameter and piston stroke Piston displacement formula: piston = bore squared 3.14 stroke displacement 4 piston =bore bore 0.7854 stroke displacement OR
piston displacement = (4 2 ) 3.14 3 4 16 3.14 3 4 150.72 4 = 37.68 (cu. in.) Example of Piston Displacement Formula If an engine has a bore of 4" and a stroke of 3", what is it’s piston displacement? OR 4 x 4 x.7854 x 3 = 37.69 (cu.in.)
Volumetric Efficiency Simply put, it is the ability of the engine to breath in on the Intake Stroke Formula: Volumetric Efficiency = actual volume of air taken into each cylinder volume of the cylinder Ratio of air drawn into the cylinder and the maximum amount of air that could enter the cylinder
Factors that impact Volumetric Efficiency Engines are capable of only 80–90% volumetric efficiency. Restrictions in the ports and around the valves limit airflow. Can you name some of the factors that would impede air flow into and engine?
Is ‘volumetric efficiency’ the same as cylinder volume? 8 to fill1 to fill BDC TDC
High Compression Ratio Pros and Cons Higher compression gives greater combustion efficiency, up to a point Efficiency goes down after a certain point due to need to retard ignition timing to avoid knock
Volumetric Efficiency and Compression Ratio Relationship Volumetric efficiency is: Ratio of air drawn into the cylinder (by the intake stroke) and the maximum amount of air that could enter the cylinder (restricted by design of intake passages, size of valve openings, valve timing and overlap ). Compression ratio is: Ratio between the cylinder volume when the piston is at TDC compared to when it is at BDC.
Amount of pressure in the cylinder on the compression stroke Measured in pounds per square inch (psi) or kilopascals (kPa) Gasoline engine compression pressure: 130–180 psi (900–1200 kPa) Diesel engine compression pressure: 250–400 psi (1700–2800 kPa) Compression Pressure Checking the Seals How is it measured? What unit of measurement is used? (Answers on next slide)
Used to measure compression pressure Using a compression gauge: screw the gauge into the spark plug, injector, or glow plug hole crank the engine note compression gauge readings Gauge readings are a good indicator of engine mechanical condition (engine seal) Measuring Combustion Pressure
Brake Mean Effective Pressure Not actually a measure of pressure, just expressed in pressure units (N/m 2 or psi) A measure of work output from an engine BMEP = Horsepower__________ (Swept volume V s ) ( rpm/120)
If one piston displaces 25 cu. in. and the engine has four cylinders, what is the engine displacement? 25 cu. in. 4 = 100 cu. in. If one piston displaces 500 cc and the engine has six cylinders, what is the engine displacement? 500 cc 6= 3000 cc = 3.0 L Examples of Engine Displacement
61.02 cubic inches = 1 litre From litres cubic inches 5.0L x 61.02 = 305CID From cubic inches litres 305 / 61.02 = 5.0L Conversion of Measurement 1L = 1000cc 1 cu. in. =16.39cc
Volume displaced by all the pistons in an engine piston displacement multiplied by the number of cylinders Units of engine displacement: cubic inch displacement (CID) liters (L) Engine Displacement bore bore 0.7854 stroke x cylinder number
Your consent to our cookies if you continue to use this website.