I only have time for a short reply now:

Off the shelf 6" connecting rods for the Chevrolet 250:
Crower Sportsman (I beam) SP91211B-6 and SP9311B-6
Scat (H beam) 2-250-600-2100

When GM re-introduced the Chevrolet 250 in Brazil from 1995 to 1998, they redesigned the engine to use 6" connecting rods.

The rod/stroke ratio has been discussed/debated for years. Some say not must practical difference, especially for street engines.

Google "rod to stroke ratio" will produce numerous articles.
A couple of articles:
http://www.hotrodders.com/forum/stroke-rod-ratio-32680.html, see post by 'deuce 454'.
http://www.strokerengine.com/RodStroke.html

Once the engine deck height has been established, 9.150" for the Chevrolet 250 unless the engine is redecked, then the following is jiggled to make it up:

Connecting Rod Length 5.700"
Piston Compression Height 1.655"
Quench Height (piston top to cylinder head) 0.030" in the hole
Stroke/2 3.53"/2 = 1.765"

In the case of Chevrolet 250, increasing the rod length to 6" allows a reduction of the piston compression height to 1.355". The new rods will gain about 40 grams and the new piston will easily loose 100 grams. The over all piston height will be reduced also for less friction. Basically one is going from a early 1960's pistion design to a 1970's or later design. The rod/stroke ratio increases from 1.61 to 1.70.

Making a grand generalization here, but pistons with a compression height from about 1.200" to 1.400" allow comfortable dimensions for good performance, wear, weight, and stability for the street. Ask the custom piston manufacturer technical reps.






Last edited by Winter; 01/28/10 01:36 PM.