Engine Measurement CONNECTING ROD – effect on cylinder wall & piston Transfer the force and reciprocating motion of the piston to the crankshaft. Small end of the conrod reciprocates with the piston and large end rotates with the crankpin Angular movement of connecting rod will cause a big impact to cylinder wall & piston: 1. Cylinders wall wear (oval) – during the engine operation (transfer the reciprocating to rotary motion) cond-rod will push hard the piston to cylinder wall (compression) and to other side of wall in power stroke. This process is repeated and will change the cylinder wall shape to slightly oval 2. Cylinders wall wear (tapered) – the above process also cause the cylinder wall slightly tapered 3. Pistons wear – piston also effect to the above process and the shape will change to slightly oval and tapered 4. Engine noise – changing direction of piston and connecting rod will cause the piston slap especially in power stroke

Engine Measurement Crank Throw distances from the crankshaft’s main bearing centerline to the crankshaft throw centerline and normally stroke of any engine is twice the crank throw Bore Diameter of the cylinder which measured in inches or mm. The larger the bore the greater area on which gases have to work Stroke The distance of piston travels up and down in the cylinder (TDC to BDC) The longer this distance, the greater the amount of air-fuel mixture that can be drawn into the cylinder and more force will result when the mixture is ignited

Engine Measurement Over Square and Under Square Engine operating characteristics differ as a result of many variables, including bore-stroke relationship & some general operating features as the following Over Square – bore larger than stroke Usually is fast revving – higher engine speeds (in revolutions per minute - RPM) Is responsive at higher engine speeds. Tends to lack low-speed torque Usually is used with a lower final drive ratio Under Square – bore smaller than stroke Usually is slow to rev because of longer stroke – low RPM engine good low-engine speed torque good fuel economy because of lower engine speed and usually is accompanied by a high final drive ratio (lower number) Square Engine – bore same as stroke good compromise between low-RPM torque and high-RPM power good low-speed torque with good high- speed power use of higher final drive ratios (lower numbers) for fuel economy, yet still maintains drivability in slow city driving

Engine Measurement Engine Displacement Volume of cylinder between the TDC and BDC that measured in cubic inches, cubic centimeters, or liters. Total displacement of engine is a rough indicator of its power output. Can be increased by opening the bore to a larger diameter or by increasing the length of the stroke Total displacement is the sum of displacements for all cylinders in an engine. Engine displacement (ED) may be calculated as follows ED = Bore X Bore X Stroke X 0.7854 X Number of cylinder or ED = ∏ x R² X L x N ∏ = 3.1416 R = bore radius or bore diameter / 2 L = length of stroke N = number of cylinders 1 liter = 1000 cc 1 liter = 61 cubic inch (cu in) 1 cu in = 16.4 cc Large displacement produce more torque than smaller displacement engines

Engine Measurement Compression Ratio ratio of the volume in the cylinder above the piston at BDC position to the volume in the cylinder above the piston at TDC position. formula for calculating the compression ratio Total cylinder volume Total combustion chamber volume Volume of the combustion chamber must be added to each volume in the formula in order to get an accurate calculation of compression ratio The higher compression ratio, more power an engine theoretically can produce As the compression ratio increases, the octane rating of the gasoline also should be increased to prevent abnormal combustion low octane rating burns fast and may explode (preignition) rather than burn when introduced to a high compression ratio. The higher a gasoline's octane rating, the less likely it is to explode.

Engine Measurement Compression Ratio After Machining There are certain changes in compression ratio after engine remanufacturing: When cylinders are bored oversize and larger diameter pistons are installed. # cylinder volume is increased # combustion chamber volume remains the same - Engine displacement and compression ratio are increases Block top surfaces are refinished (called "decking the block“) # increases the compression ratio because it results in the cylinder heads being down closer to the tops of the pistons Cylinder heads are resurfaced # increases the compression ratio

Engine Measurement Compression Ratio After Machining To calculate the exact compression ratio of the engine, exact measurements must be made of the bore, stroke, and combustion chamber volume. Compression ratio = PV + DV + GV + CV DV + GV + CV PV = Piston volume DV = Deck clearance volume {volume in cylinder above piston at TDC) GV = Head gasket volume = Bore X Bore X 0.7854 X Thickness of gasket CV = Combustion chamber volume

Engine Measurement Compression Ratio After Machining What is the compression ratio of V8 engine with 4.000 inch bore, 3.480 inch and zero deck clearance volume, if the only change was to install 62 cubic centimeters instead of 74 cubic centimeter cylinder heads? Bore = 4.000 in Stroke = 3.480 in CV = 74cc (4.52 cu in) CV = 62 cc (3.78 cu in) GV = Bore X Bore X 0.7854 X Thickness of compressed gasket = 4.000 in X 4.000 in X 0.7854 X 0.020 in = 0.25 cu in PV = Bore X Bore X Stroke X 0.7854 = 4.000 in X 4.000 in X 3.48 in X 0.7854 = 43.73 cu in (350 cu.in / 8) With 74-cubic centimeter (4.52 -cubic inch) heads CR = (PV + DV + GV + CV) / (DV + GV + CV) = (43.73 + 0 + 0.25 + 4.52) / (0 + 0.25 + 4.52) = 48.5 / 4.77 = 10:1

Engine Measurement Compression Ratio After Machining With 62-cubic centimeter ( 3.78-cubic inch) heads CR = (PV + QV + GV + CV) / (DV + GV + CV) = (43.73 + 0 + 0.25 +3.78) / (0 + 0.25 + 3.78) = 47.76 / 4.03 = 11.9: 1 Conclusion compression ratio was increased from 10:1 to 11.9:1 by just changing cylinder heads from 74 cubic centimeters to 62 cubic centimeters 11.9:1 compression is usually not recommended for use with today's gasoline, this change should only be done for racing purposes where expensive fuel or fuel additives will be used