59 connecting rods

[John Farwell]

Anyone know or recommend a good connecting rod for the $. Looking for a small journal, I beam, 5.7, standard rod for a steel crank...building a stock 290HP car....thanks...John

[Duke W.]

Re: 59 connecting rods

I agree that you should replace the OE rods. They are weak!!!

The small bearing rod went through a number of design changes from '55 to '67, which was the last year that GM built small bearing small blocks. The final version, 3864881, went into production in the late '66 or early '67 model year.

The 881 has the same finished machine dimensions as 283 rods though it might require heavy metal to be added to the crankshaft for proper balance, since it is a bit heavier than 283 rods, or alternatively, the rod can probably be lightened by grinding off the balance pads to obtain big and small end weights that won't require heavy metal to balance the crankshaft.

For mechanical lifter 327s, which have an earlier rod than the 881 I usually recommend Crower Sportsman rods if you want a bullet proof bottom end. The 881 is probably okay for L-79s and definitely okay for lower revving 327s. Since a 283 has a shorter stroke and a lighter piston than 327s, the 881 rod should be adequate for a street 283 limited to 6500 revs, and it is certainly a significant improvement over the OE 283 rods.

If you do a search I believe it was Mike Ernst who lost a rod in his '57 FI a few month ago, so you are well adviced to find a better rod.

The 881 may be available from other sources than GM, such as Federal Mogul as I don't think GM actually manufactures these rods, but they are done by a supplier and other retail sources may offer the same rod.

If you e-mail me I will send you some side by side photos of the late and early 327 rods where you can see the difference, particularly around the rod bolt seat, which is the critical stress area, and I think the earlier 283 rods are even more spindly looking than the early 327 rods.

Duke

[Joe L.]

Re: 59 connecting rods

Duke and John----

I agree. If you are doing a rebuild on a 283, I'd replace the rods.

The GM #3864881 would be a good choice. These rods have been discontinued for quite a few years, but reconditioned sets are available. As far as value goes, a reconditioned set of these will be quite economical and far better than the original 283 rods. Of course, you will have to rebalance the reciprocating assembly, but you should do that anyway. Incidentally, these rods, when they were still being manufactured, were actually manufactured in-house by the old Flint Engine Plant (and, for that matter, the Tonawnada engine plant, too). You may be able to purchase similar NEW rods from sources like Federal Mogul/TRW, though.

The Crower Sportsman would be a better choice, but they won't be as good of a value. A set of these rods will cost about $500 for the 283 application. They'll support 8,000 RPM and 500 hp, which is probably a lot more rod than you need. But, I'd probably go for them.

[GL Anderson]

Re: 59 connecting rods

Scat now makes a forged rod with ARP bolts in the small journal size. They can be bought for $250 or so for a set. Supposed to be good for 500HP. GL

[Patrick H.]

Re: 59 connecting rods

I think Joe would prefer them hypereutectic over forged.



Sorry, old inside joke for the few of us who have been around since the site started.
I can feel Joe glaring at me across the country....

Patrick

[Joe L.]

Re: 59 connecting rods

Patrick-----

Actually, I've never been an advocate of hypereutectic cast aluminum connecting rods. If they made them, I probably wouldn't buy them. However, I am an advocate of hypereutectic cast aluminum pistons. GM is, too. In fact, they'll be using them on the new LS-7 engine. Now, given the fact that they're also using titanium connecting rods, titanium intake valves, and sodium filled, high alloy exhaust valves, does anyone really think that GM is using hypereutectic cast pistons over forged to save money?

[Duke W.]

Re: 59 connecting rods

I think GM's reason for using cast pistons in the LS7 is the noise issue though there is some controversy about exactly what type of pistons they will be using as both types have been stated in GM press information and GM reps at this years round of new car shows.

Guys whinned like babies because the '01 LS6 had pistons with a slighty looser fit and they made a little noise when cold, so they tightened the clearance and applied a polymer coating to help prevent scuffing. Guess none of them ever experienced a mechanical lifter SHP engine from the sixties.

Hypereutectic cast piston's are probably adequate for the LS7 except for maybe an engine that will be seriously raced, but I think forged were taken off the table due to their greater required clearance, which would have brought no end of customer complaints about "engine knocking".

Duke

[Mike E.]

Re: 59 connecting rods

Duke--
Thanks a lot for reminding everyone! It indeed was me--motor will soon be going back together.

[Patrick H.]

Re: 59 connecting rods

Joe,

I thought you never forgot things....

Or should I ask Wayne to stop by?
The infamous forged vs. hypereutectic piston argument.
I think that's the only time you've ever gotten really riled up on the Board.

Patrick

[Joe L.]

Re: 59 connecting rods

Patrick-----

Oh, I haven't forgotten that. That was during the period of the "interim" discussion board format. However, don't look for Wayne; look for "Wayne".

[Joe L.]

Re: 59 connecting rods

Duke----

I think that the noise generated by "piston slap" is very likely ONE of the reasons for GM's choice of hypereutectic cast pistons over forged.

There's no question that forged pistons offer more ultimate strength than cast. The question is how much strength is NEEDED versus what do you have to GIVE UP with a forged piston? If you can achieve all the strength that's NEEDED with a safe margin of extra strength above-and-beyond that, why give up all of the other things that you need to with a forged piston?

If you look at other components, a crankshaft or connecting rods, for example, when you used forged components rather than cast, you don't give up anything except cost. If you use these components in a run-of-the-mill, grocery-getter engine you won't lose anything except cost. For an engine like the LS-7, a cast crank would probably work just fine. However, the extra strength provided by the forged crank is nice "insurance" and you don't give up anything, except cost which is somewhat "irrelevent" here, to get it. Many high strength components are this way.

Pistons are an exception. There, to get ultimate strength, there are associated penalties. So, a balance needs to be struck and a prudent choice made. Hypereutectic cast pistons provide nearly all of the strength advantage of a forged piston without all of the disadvantages of a forged piston (e.g. noise, higher wear rate, and associated higher oil consumption). To me, the choice is a "no brainer" for a street engine, even a SHP street engine like the LS-7. If these pistons had been available in the 1960s, I feel pretty confident that GM would have used them on the SHP engines of that era. They weren't, though, so they couldn't. One can now, though.

The new GM 8.1L big block uses hypereutectic cast pistons for all variants, including marine. Marine validation testing is among the most "strenuous" there is. If these pistons will hold up in this application in a big block, they'll work just fine for ANY street application.

For racing use, of course, the balance shifts the other way. There, to gain the ultimate strength of a forged piston you don't give up anything that's very important as far as racing priorities are concerned. So, a forged piston is definitely the way to go. If I were building an engine for racing, I would definitely use forged pistons. For ALL street applications, though, I consider the hypereutectic cast to be the only way to go. Cost, incidentally, is really no consideration, at all, as far as I'm concerned. The cost difference between hypereutectic cast and forged is really insignificant. It's about a difference of $200-600 per set. In my case, for example, it will cost me about $20,000+ for the "ZL-1" when all is said-and-done. So, what's $200-600 extra for a set of pistons? Quite frankly, I'd use hypereutectic cast even if they cost MORE than forged. And, I'd still use them even if they cost a LOT MORE than forged.

[Patrick H.]

Re: 59 connecting rods

You think it was an imposter?
On that board, who knows. I'm surprised we're still around after that mess.

Oh, that's right. It DID get shut down.

I'll never forget the look you gave me across the picnic table at lunch in Bloomington (well, the Interstate Ctr) that year when I asked you about the forged pistons for your ZL-1.

It's been quite a few years that we've been here now, hasn't it. Several permutations of the Board(s), too.

Patrick