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jluetjen jluetjen is offline
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Join Date: Oct 2001
Location: Westford, MA USA
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If this is true the engine must produce more torque. The lever arm of the crankshaft is longer.
True, by a whopping 4.4 mm in the case of the 2.4/2.7's 70.4 mm crank compared to the 2.0/2.2's 66 mm crank. But be sure to add in (subtract?) the energy involved to accellerate the reciprocating masses harder in each stroke. You also have increased friction due to larger rod angles resulting from the shorter rod length, basically a short stroke/long rod engine is better at converting the pressure on the piston into lateral motion, while a long stroke/short rod engine wastes more energy trying to push the rod sideways.

The big benefit of a "long stroke/small bore" engine is that it is easier to optimise the combustion chamber shape while maintaining a high CR. One of the biggest challenges for F1 designers working with VERY short stroke (40mm's) - BIG bore engines (94-100 mm's) is that the combustion chamber gets wider and wider and flatter and flatter because of the big bore and the big valves needed to pull all of the air needed at 19000 RPM. It gets real tough to have clearence for valve overlap at TDC without pockets in piston, which reduces the CR again. The 2.0S's had a similar problem.
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'69 911E

"It's a poor craftsman who blames their tools" -- Unknown
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Old 12-12-2003, 11:38 AM
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