buick-rover-v8
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 ```>Lar Kaufman wrote: >> It's quite easy to figure out displacement if all you do is change the >> stroke. Your current displacement is 100%. Multiply that times the >> percentage of additional stroke, and add that to your original >displacement. > >I don't think this is true - assuming we mean displacement to include >combustion chmaber space as well. If we mean displacement to only mean >that volume displaced by the pistons as they move, then it probably is >true. > >If the combustion chamber in the cylinder head did not exist and the >pistons had flat tops, it would be true because the cylinder would then be >a true cylinder. However, in the case of an engine, any depression or hump >in the pistons and also the combustion chamber volume has to be accounted >for. > >If the combustion chambers space = A, the piston hump or depression = B (+ >or -), and the cylinder vloume = C, then the engine capacity is equal to >No. of cyls * (A + or - B + C). > >Increasing the stroke by X percent would change the formula to: > No. of Cyls * (A + or - B + (C * (100+X)/100)) > >Regards, > >Ron Beckett >Editor / Webmaster, LandRover Owners Club of Australia >Webmaster/Database Manager, Hillman Owners Club of Australia ************************************ Ron, Interesting subject. Let me try to clarify (or muddy?) the waters some----- I am not sure just what the various terms you use mean in Australia--I am sure there are some differences compared to the U.S.A. Over the years here, I have always observed displacement to mean only the swept volume in the cylinder(s). I think another term may be capacity (or cubic capacity). It is just the volume available to fill with fuel/air mixture on each intake stroke and empty of exhaust gas on each exhaust stroke. The volumes of the combustion chamber, head gasket space, piston dish, and deck clearance are thought of as only affecting compression ratio, not swept volume, or displacement. These volumes are filled at all times with either air/fuel mixture or exhaust gas. They never fill or empty during engine operation. I have often heard of these volumes collectively refered to as clearance volume. By these definitions a piston dome would have a negative volume, thereby reducing clearance volume, and increasing C.R. The basic displacement formula is (pi)(bore)(bore)(stroke)(No. of cyl.)/4, as I'm sure you know. Since the stroke is a factor only to the first power (not squared), Lar's statement is completely correct on the basis of the above definitions. Simply divide the displacement by the old stroke and multiply the result by the new stroke and the new displacement appears--a direct proportionality. Or do it by Lar's percentage method--the 2 are exactly equivalent. However, if we take displacement to include any of the clearance volume components (or all), then the simple relationship disappears, as you correctly state. A change in stroke only affects part of the displacement in that case and we no longer have a simple proportion problem. Hope nobody was bored to death by that one. Regards, Dave Kernberger ```