Connecting rods.........
 

Is there any material difference between the con rods used in the 1974-77 911S and 3.3 ltr turbo engines and those for the 1978-83 SC engines? This question is prompted by the fact that I have a set of rebuilt and balanced rods that appear to be either 74-77 911S or 76-77 930 rods which I would like to use in a forthcoming 3.3 SS engine build based on a 3.0 SC engine. The measurements all appear to match those for the SC rods but I don't want to make an expensive mistake!

Thanks,

The measurements are the same for all the rods you are talking about. The 2.4L S spec rods were nitrated for greater strength/durability.

Conn rods
 

It seems that the only difference in the 2.7 and 3.0 SC rods is the thickness of the large end. The 2.7 rods are a bit over 23mm thick (side to side) and the SC rods are in the 21.7-21.8mm range. The rods that I have measure 21.76mm so the should be perfect in an SC based engine. The small end is bushed and honed for a 22mm piston pin and the overall length is the same for both models. The rods that I have weigh in at:
1 702 grams
2 702 grams
3 702 grams
4 703 grams
5 704 grams
6 702 grams

The factory delta for a rod set is a max of 9 grams so these should be fine. All they need now is a new set of rod bolts and nuts.

Strangely enough, I've just weighed my 965 rods (930 part numbered, though) for my rebuild...without bolts, nuts and shells, they're a fair bit lighter than the ones you describe above ---> Spencers rod weights

Small ends now bushed for a 22mm pin, and have been checked for centre-centre dimensions and ovality (although I don't believe any correction work was needed)

....not being confrontational, just a casual observation....it's been tonights activity plugging the numbers into Excel to get the combinations to balance.

Ta
S

Rod weights
 

Spenny_b,

Your rods are probably based on the Carrera rod (1984-89) which is supposed to be lighter than the earlier 911S and SC rods. Also, the set that I have are at the upper end of the scale weight wise. I haven't weighed a set of rod bolts and nuts separately but they would be a factor also as the earlier rod bolts were heavier than the later ones. In fact, the reduced size of the Carrera rod bolts is one reason that it is recommended they be replaced with ARP or other aftermarket bolts. Thanks for entering the conversation and adding to the knowledge base!

Cheers

Hi Fred,

Well, out of curiosity, I did also weigh the OE rod bolts yesterday as well. Strangely (to me at least) the stock bolts and nuts (used on the 965 rod) are 33gsm apiece. The ARP's are 34/35gsm each.

That did surprise me, as that chunky hex nut on the stock bolt looks far heftier than the beautifully made ARP multi-point nut. I guess the weight is in the ARP bolt itself?

No probs ;) am enjoying the learning!

Waynes book on rebuilding has all the weights in it for the con rods...with bolts they are all in the 600-700 gram range.