Direct Connection RB connecting rods

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Mecki

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I got a set of DC connecting rods for the RB. These are old school from the 70ties and they were offered as the P-3690649. Obviously these are not the 649-rod offered as a stronger substitute for the LY-rod. According to the DC catalog from -75 they were as the LY forging but made of better material without adding weight. The DC engine manual I have (P4349340 From the 80ties) has a picture of the 649-rod and it has a casting number P4120516 and the small end is not rounded.

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So I did some measuring. The weight of a rod in this set is 1010g +/-1g. Well matched. The length is 6,760" instead of 6,768". Small end 1,090" press fit pin. The small end is rounded and there is no numbers on the beam. I have understood that the Hemi Forgings did not have any numbers on them. So I would think these are the Hemi Forging RB-rods. The confusion is that the Hemi Forging made for the RB P-2531589 should have 7/16" bolts. These I have are with 3/8" bolts. Was such an option also available?
 
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From the -75 Direct Connection catalog:
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The DC engine manual states that the Heni Forging P2531589 machined for the RB only is 6,760" long instead of the stock RB that is 6,768". (Some other sources claim that the Hemi Forgig RB rework has the stock RB 6,768" lenght.)
The stock street hemi rod lenght is 6,860".
I was just wondering why these have the 5/8" bolts and not the 7/16". Makes no sense if they are really the strongest Hemi Forgings.
 
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Do u not mean 3/8s bolts as in all the factory RB rods. 5/8s is 4 sizes bigger. As in 3/8s, 7/16s, 1/2, 9/16s then 5/8s. I doubt there would be room to have a 5/8s bolt and nut as u would probably need to notch the block also Kim
 
You are absolutely right. 3/8" is what I meant, Being familiar with and using metric daily sometimes results in this kind of errors. We don't use or even have other than metric measures so it has always to be converted. For me the measures are 9,525mm and 11,1125mm when measuring 3/8" and 7/16".
 
The 3/8" bolts can be replaced with stronger 7/16" bolts so that's no concern. The main concern is how to balance.
The stock LY rod is 846g and the street hemi rod 1084g (from the FSM). I could not find any weight for the Six pack rod in the FSM but somewhere was said that it's around 33oz = 936g and that the hemi rod is about 35oz = 992g.
Looking at those figures and comparing with 1010g for these rods it seems that even the external balancing like the Six Pack uses is not going to be enough.

I suppose the Hemi crank is much heavier and has much more counterweight than the stock RB crank, since as I have understood the Hemi is internally balanced.

Whats the way to go to balance Hemi Forging rods with a stock RB crank and pistons?
I realize that the easiest and maybe cheapest would be to abandon the idea (and I probably will), but just for interest, how did they balance these Hemi Forging RB setups back in the day when these were the hottest setup for a RB?
 
You'll likely have to put Mallory in a couple of counterweights with that much heavier of a bobweight....
 
I do not know what these rods are, but I replaced them with Molnar H-beams. Over 4 lbs taken out after rebalanced. Hemi. Look at how it was balanced. There was lead behind the Mallory slugs and then the welded weight at the flange.
Get on a diet.

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