Comments by "mpetersen6" (@mpetersen6) on "Engineering Explained" channel.

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  4. I seen info that the ideal stroke to rod length ratio is 1.75. How true that actually is I'm not sure. Stan Wiess has a web site with data on rod ratios, bore and stroke etc. A Chevy 327 is 1.7538. A Buick V-6 or 300 SB is 1.7529. A lot of Hondas are around 1.5. The only engine I can find data on that is right at 1.75 is an AMC 232. There's another factor that enters into this. And that's deck height. Plus with a really small bore and long stroke you start running into clearance issues unless the bore is noted or the deck height gets really tall. Big bores raise another issue. Unless you siamese the cylinders the crank gets really long. A good example of the effect on deck height is the Boss 302 vs the 302 in the Z-28. Both 4" bore with a 3.0 stroke. But the Chevy rod 5.700 while the Ford is 5.150. The rod to stoke ratios are 1.8968 vs 1.7166 respectively. The Ford could actually accommodate a longer rod by the use of a piston with the wrist pin higher in the piston. There are a large number of factors involved in the design of any engine. Longer rods, more reciprocating mass. Short deck height, smaller packaging. Plus on a OHV engine lower deck height, shorter pushrods*. Yes I know OHV is practically prehistoric technology. But ask yourself. Just how many drivers really make use of all the engine power they have any way *Another way to shorten push rods is to make the rocker arms so the pushrod seat is below the pivot point of the rocker. Another way is to place the camshaft much higher in the block so that the lifters are pretty much even with the deck face. Renault actually built a 1.6 liter with this set-up. Very short pushrods, cross flow head and a hemispherical combustion chamber. I've often wondered just how a V-8 with 2 camshafts mounted high in the block would be like. I don't know if it's ever been done.
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