Engine size computation?

2007cc

Go play here if you want:

Jan

The formula is Pi*R2*S for 1 cylinder. That breaks down to 1/2 the bore size squared (radius) * 3.14159 * stroke. This gives you the volume of one cylinder then * the number of cylinders.

9.05 /2 = 4.525 4.525 squared = 20.475625 20.475625 * pi = 64.32601874375 64.32601874375 * stroke 7.8CM = 501.74294620125

This is 501.74294620125 CM3 per pot and then *4 to round the engine to

2006.971784805 CM3. The usual rounding of decimal places would give you 2007 CM3.

Tony

also note that you crank stroke may be something other than what it was sold and advertised as. MANY "78mm" cranks are actually 78.6mm. This makes a huge difference in compression ratio for example..

Jan (80x90.5 in the works)

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...and many 74's were actually 73.8

Prior to using any crankshaft that is new or just back from the re-grind shop, it pays to set it up on vee blocks and verify the throw-length on all four.

-Bob Hoover

This makes perfect sense but it's also something I never considered before. How likely do you think it is to get a crank where the individual throws have a different stroke?

Tony

A good point an additional .6mm stroke with a 90.5mm bore will make a 20 CM3 difference in a 4 cylinder engine.

I now wish I had checked the stroke on the crank of the perpetual project engine before I put the heads on... However the calculated CR is a little less than 8 to 1.

Tony

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Dear Tony (and the Group),

The liklihood is virtually 100%. The real question is HOW MUCH does the part deviate from the allowed dimensions.

Tools and grinding wheels wear. Components have to be mounted in jigs and the raw part may not be a good fit or the person doing the mounting may be feeding a battery of machines... lots of ways for a brand new part to end up out of spec. And even more ways for that to happen today, with the typical engine containing parts from a dozen different manufacturers scattered around the world.

Volkswagen employed three inspectors for each assembler or machinist. Nowadays, lotsa shops cranking out VW after-market components use wet-back labor working for piece-rate wages and don't have any inspectors at all. It's not uncommon to open a box of supposedly new P&C's and find a mixed bag of weight groups, or to sort through five sets of 'rebuilt' connecting rods without finding four that are in spec.

Any mechanic who builds GOOD engines knows that nowadays the hardest part of the task is simply finding good parts. Nor is there anything new in WHY this is so... A fellow named Adam Smith described the phenominon more than 200 years ago.

-Bob Hoover