331 vs. 347 Stroker

[Chevyguy]

Ok, I'll throw a bone in here.

My grasp of the 347 vs 331 issue falls into the rod vs stroke ratio.

The 347 with the 3.4 stroke and a 5.09 rod = 1.497 I figure I am off somewhat on the stock ford rod length but follow me here.

The Stock 302 3.0 stroke 5.09 rod = 1.696

3.4 stroke and 5.4 rod = 1.588

3.25 stroke and 5.09 rod = 1.566

3.25 stroke and 5.4 rod = 1.6615

A Chevy 350 3.48 stroke 5.7 rod = 1.638

327 3.25 stroke 5.7 rod = 1.754

Chevy 302/283 3.0 stroke 5.7 rod 1.90 !!!

Chevy SB 400 3.75 stroke 5.56 rod 1.483

3.75 stroke 5.7 rod = 1.52

3.75 stroke 6.0 rod = 1.60


Now you figure, what the hell is he talking about

Where the reliability issue comes to play is the side loading of the piston. Having a low rod to stroke ratio pulls the piston toward the side of the cyllinder at the bottom of the stroke. This makes for a less revving motor and can cause excess wear on the piston. On the other hand, the Chevy 302 with the big 2.02 valves and a 1.9 rod to stroke ratio will rev to the moon.

The stock Chevy 400 was thought to be a big POS for years until they started to put 5.7 or 6.0" rods in them. Note how low those rod/stroke ratios are.

I imagine the first 347 kits used the stock rods and had some problems with piston wear, with the 5.4" rods they should be ok.

The 3.25 crank and stock rods is almost as good as a 5.4 rod 347, and 3.25 crank and 5.4 rods is pretty good