Direct Connection RB connecting rods

[Mecki]

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.

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?

 

[oldkimmer]

Those rods look nice. Hemi rods are also .100 thou longer than RB rods. Chrysler often supersedes part number every so often. Kim

 

[Mecki]

From the -75 Direct Connection catalog:

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.

 

[oldkimmer]

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

 

[Mecki]

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".