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      09-26-2013, 08:23 AM   #25

Drives: No BMW for now
Join Date: Jun 2006
Location: Canton, MI

iTrader: (1)

Originally Posted by Boss330 View Post
A oversquare design is better for a high revving engine as that keeps piston speeds down. Lower piston speeds is good for durability. One of the disadvantages of a oversquare (short stroke) is lack of/less torque than a similarly sized undersquare engine.
Right. So, if an over square engine is good for high revving operation then why did BMW force an under square design onto the ~8000 RPM S54, only to turn around and reverse that for the ~7500 RPM S55. You see? Your rationale does not cover it. I am not saying you are wrong, but there is very clearly more to the story.

More torque? Ok, let's prove it.

Remember that a long stroke means a longer arm from crankpin to crank center, and as we all know Torque = Force x Arm. So the longer the stroke, the longer the arm from crankpin to crank centre is and more torque is made.
How much more torque, then, from the engine with the longer stroke? Can you calculate it? Before you run those numbers, let's keep in mind that any increase you make in stroke while keeping displacement and cylinder count the same means a commensurate decrease in bore.