Balancing Vs. Rod Length SB's
Conn Rods 5.700 vs. 6.000
There's a tremendous amount of really misleading information posted up here from time to time pertaining to balancing units and rod length selection. The rod length has very little effect on the overall operation and may be even helpful to the shop doing the balancing. A heavier "bobweight" means less drilling (less labor) for the shop. Normally you would think because the 6.000" rod is heavier that the job will be easier due in part to a lighter (shorter) piston. It doesn't work out this way. If you choose the right crankshaft, I'm talking 4340 and sold as an "internal" unit most will now make the bobweight with no "fill", regardless of the rod length. Eagle's 4340's are down to an
"1850" target. READ THIS CAREFULLY: I have 2 400 SB's just off the balancer (3 weeks ago). Both units are 406" (4.155"), ESP SIR(LW) rods, and Ross
"flat-tops". The first has the 5.700" (535 Grams) rod and the piston #90008 (455 grams), the other has the 6.000" rods and #90007 (406 Grams) pistons. The bobweight for the 5.700's is 1604 (using 92 gram Ferrea pins) and for the 6.000's is 1649 (also with the 92 gram pins). You can "see" that the 5.700" rods would be an advantage in this case, both to help in balancing and also for "lighter" internal parts. All the cranks we use are "profiled" for the 5.700" rods, regardless of the rod we use. There are a couple of advantages to the "longer" rod, however. First and most important, it takes some loading off the bores, which in a stock G.M. block is a definite plus, and second, the "dwell" time produces a much "cleaner" burn when it "fires". One other issue while I'm here pertaining to the choice of blocks used to build around. If you take all the components (the ones you're going to use) and choose any "aftermarket" unit, whether it's G.M., Dart, or World, you'll see up to an add'l 20 HP over a stock G.M. 400 casting. This we've tested most recently. Thanks, Gary in N.Y.
P.S. The pistons are sold from Ross with 120 gram pins, but we don't use them, if you choose to keep them you'd add 28 grams to both bobweights. Rick D., if you catch this post, pay close attention to it, this is all fact.