Longer rods provide for a longer dwell at piston TDC, keeping the combustion chamber small for a longer period as the expanding gases push against the piston. This extracts more power from a given air/fuel mixture thus increasing combustion efficiency. And so much like with good quench, you've once again raised the amount of compression that you can utilize for a given combination (and octane) before detonation becomes a concern. Also, much as does a stroker set-up, longer rods benefit the power band (read "torque curve") with the largest advantages in the low and mid-range RPMs. Even in a stock bore and stroke combination, longer rods can give you some of the effect of a stroked engine. And in fact on a shorter stroke, an even longer rod can be used within the given limits of practicality, this meaning pin location on the piston. While on a pure race engine, particularly such as in a drag race application where run durations are minimal, pin location can be pushed to the limits. But for a long living street engine there are other obvious considerations. Still, with a 350 Chevy (3.48" stroke), a 6.125" rod (5.7" is stock) can be used with no problems, with the correct piston of course. For a 383 (3.75" stroke), you'd probably want to limit it to 6" for street. I use a 6" rod with a 3.80" stroke in my LT1 that does put the pin slightly into the oil ring land. But by using oil ring supports, this is not a big deal.

The reason the 340 Mopar still manages to have a broad and strong torque curve, even with a very short stroke of 3.31" is the fact that this stroke allows it to use rods that are just under 6 1/8". I can't help but wonder if it was simply a cost-saving matter for Chrysler to keep the stroke the same for the 340 as it was in the 273 (and 318) or were they ahead of the curve in experimenting with rod length combinations? Perhaps it was some of each....

One other important benefit of longer rods is that they also reduce side-loading against the cylinder walls. This in turn reduces friction, heat and so of course, wear.

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