Can somebody tell me how to read this terms (1.2:1 bore:stroke) and also how to read the compression ratio????
Bore to stroke ratio: compare the bore diameter of the cylinder to the stroke of the cylinder at BDC. Example: 4.030 bore, 3.4 stroke: 4.030/3.4=1.185:1. This is the bore stroke ratio for the popular 347 stroker that people build with 5.0 blocks 4.030, 3.25 stroke:4.030/3.25 = 1.24:1. This is the bore/stroke ratio for the popular 331 stroker built from a 5.0 block. Simple definition of compression ratio: total volume of the cylinder at bottom dead center (BDC)divided by the volume of the cylinder at top dead center (TDC). Example: if the BDC cylinder volume is 600 CC and the TDC cylinder volume is 60 CC, the compression ratio is 600/60 = 10:1. Compression Ratio = Total volume of cylinder at BDC divided by Combustion chamber volume + volume of deck (area between top of piston, including valve reliefs and bottom surface of head). The deck volume is hard to estimate. The practical way is with the engine mounted in an engine stand to crank the cylinder up to TDC, tilt everything until the bottom of the spark plug hole is the high point and pour in light oil using a graduate (measuring glass marked off in CC'c). Take note of how much oil you poured in until it reached the bottom thread of the spark plug hole this is Combustion Chamber + Deck Volume, or CCDV. Crank the engine to BDC and pour more oil until it reaches the bottom of the spark plug hole again. Subtract reading one from reading two: this is your Swept Cylinder Volume or SCV. Divide SCV by CCDV and you have your answer. Hope this helps. Come to think of it, positioning the spark plug to where it is the highest point on the engine may not be so simple after all, but you get the picture.
