A rod ratio of less than 1.8:1 increases side thrust and hp loss at high-rpm when comared to ratios over 1.8:1.

A rod ratio of more than 1.8:1 decreases side thrust and hp loss at hi-rpm, when compared to ratios below 1.8:1

Long rod engines have longer, heavier blocks or shallower, more expensive pistons. The added weight, or extra cost, crosses out the benefits. One the street, rod length ratios of 1.48 to 1.56:1 work well...its only in racing situations when you'd consider a change.

Fords are often in at the lower, 1.48-1.56:1 ratio because of the cost of tooling different block heights. Chrysler tends to optimise rod length for each of its engine families, Ford don't. 225 Slants are at 1.6:1 with there long-stroke six. You seldom see 1.56:1 ratios on their engines. Only exception is the 215/245265 Aussie Hemi i6's.

Poor rod ratio engines can still perform well, its just that high-rpm power will be less than if a longer rod goes into the engine. This has nothing to do with bore:stroke ratio. Increasing the piston area raises top end power.

NB: The ratio is rod centre to centre length divided by stroke.

Here are some common ones for Aussie, Argie, and Americans to ponder.

**400** has rod ratio of 1.65:1, bore to stoke ratio 1:1 (square) Very tall block

**351 M** has rod ratio of 1.88:1, b:s ratio of 1.14:1 (oversquare), very tall

**351 W/K** has rod ratio of 1.70:1, b:s ratio of 1.14:1 (oversquare), tall block

**351 C** has rod ratio of 1.65:1, b:s ratio of 1.14:1 (oversquare), shallow

**302 C** (Aussie 351C, destroked) has rod ratio of 2.01:1, b:s ratio of 2.01:1 (oversquare), shallow

**302 W** has rod ratio of 1.70:1, b:s ratio of 1.33:1 (oversquare), v. shallow

**302 Boss **has rod ratio of 1.72:1, b:s ratio of 1.33:1,(very oversquare and short block)

**300 I6 **has 1.56:1 rod ratio, b:s ratio of 1.01:1 (square), very tall block

**289 W** has rod ratio of 1.80:1, b:s ratio of 1.39:1,(very oversquare and short block)

**260 W** has rod ratio of 1.80:1, b:s ratio of 1.39:1,(very oversquare and short block)

**255 W** has rod ratio of 1.70:1, b:s ratio of 1.23:1 (oversquare), v. shallow

**250 I6 **has rod ratio 1.51:1, b:s = 0.94:1, (undersquare, tall block)

**4.0 Intech SOHC/DOHC I6**, rod ratio 1.53:1, b:s = 0.93:1 (undersquare, tall block)

**3.9 SOHC I6**, rod ratio 1.51:1, b:s = 0.92:1, (undersquare, tall block)

**240 I6 **has 1.95:1 rod ratio, b:s ratio of 1.25:1 (oversquare), very tall block

**221 I6 **has 1.49:1 rod ratio, b:s ratio of 1.06:1 (oversquare), medium block

**221 W** has rod ratio of 1.80:1, b:s ratio of 1.22:1,(very oversquare and short block)

**200 Geelong I6 **(Aussie 250 destroked) has 2.01:1 rod ratio and 1.178:1 b:s ratio (oversquare), tall block

**200** (All US and pre 1970 Aussie) has rod ratio of 1.53:1, and 1.178:1 b:s ratio (oversquare), shallow block

**188 I6 **has rod ratio of 1.83:1, b:s ratio of 1.25:1, (very oversquare and medium block)

**170 I6 **has rod ratio of 1.60:1, b:s ratio of 1.19:1, ( oversquare and short block)

**144 I6 **has rod ratio of 1.88:1 ( I think), b:s ratio of 1.40:1, (very, very oversquare and shallow block)