[Green Elephant]

I have a mild 389 build going together and had considered reusing the stock early forged rods with ARP bolts.
After reading several posts on this website I decided to use a set of Eagle rods instead. I had no idea those early forged rods were so suspect.
I wanted to say thank you to everyone for posting your experiences here, not just with connecting rods but many other Pontiac related issues as well. Your experience has saved many of us from the same heartaches you’ve had in the past.

[tom s]

Dont use them unless they are 62-63 421 SD rods.The early rods were called the rubber rods.Low heat treating.Tom

[433lemans]

I will just throw this in here. Maybe I was lucky.
Back in the early 1980's when I drag raced my 69 Lemans, that I still own, it had a 428 +0.030. Crane Fireball cam, #16 d port heads from a 68 GTO I owned. TRW forged pistons and early factory forged rods that came out of a 62 Catalina tripower car I owned. I did a lot of things wrong when I raced it that I won't get into here and one of them was over revving this motor to 6000 to 6200 rpm on each pass. Two seasons. I ran a best time of 12.33. This motor lived thru those rpm's, including the rods. The rods never had any special treatment except balancing.
Again, maybe I was lucky but I would use them again in an economy rebuild. JMO

[Formulas]

Measuring the rod boss from under the bolt head to under the nut will tell you what version you have, Think that info is in a old H.O. Racing pub.

[steve25]

The early rods rebuilt with new bolts and run in 3.750” stroke motors at no more then 6500 rpm in street use motors with street gearing ( no faster G force loading from 4.11 or steeper gears ) are fine.

However even when rebuilt with ARP bolts,
polished from top to bottom,
shot peened ,
lightened a good amount
run with lighter pistons and pin’s your going to have
Disastrous problems in a 4.210” stroke motor when run to 6400 rpm at some point.

This is from my experience.

The second series of forged rods used in all the 421 non SD motors where responsible for a lot of blown up 421 motors even though the stroke was only .250” more.

The measurement of the spread of the rod bolt pads is not a 100 % guaranteed way to tell if you have a SD rod.

I have a few that by the pad measurement you would say they are SD rods, yet they are not.

[67Lemons]

I’m really starting to question all these weak rod comments, was just thinking about it this weekend in fact. I haven’t seen anyone on any forum in recent years comment that they lost a rod in a street motor. I know a lot of builds have new rods but how many other stock motors are out there getting the snot beat out of them with no issues? I see cam or lifter issues almost every day but not rod issues, if they were so weak I’d think the street section would be filled with complaints. Just my opinion of course.

[PontiacFan428]

If you had to choose between rubber rods or cast rods, which would you choose and why?

[steve25]

Tuff call, but I would go with rebuilt and side beam polished cast rods out of a less the 100K mile 2 bbl motor if I could without question in a street motor that would not be called upon to spin more then 6000 rpm in a 4.210” stroke motor, or 6500 rpm in a 3.750” motor.

Also a lot of weight can come off the pin bore area on the cast rods.

For a factory motor to go into production it had to run at 4500 rpm at full throttle for 100 hours with only a stop long enough at 50 hours to change the oil and filter.

[tom s]

I would and have run the late cast rods in a non high rpm street engine.Tom

[grandam1979]

In the 80’s and early 90’s I used to run junk yard shortblocks. I had a good set of 62 heads I would use with a blueprint r/a IV cam comp roller tip rockers. The fastest one was actually a 74 455 shortblock that came out of the yard at 130,000 miles. I would run a 125 nos kit the car went 12.40’s on engine 11.40-11.60 on the nos. I did this and never broke a rod I spun rod bearings but the car got me home every time. It spun one bad enough the piston was taking the shape of the chamber. Not Pontiac related but the worst engine fail I had was a .030 over 454 in my t bucket when it went the only thing good was the intake and starter it even broke the trans.

[Sirrotica]

I have a 428 that I ran 2 1/2 seasons with the heavy TRWs with late cast rods a complete build that was retired in great shape. Every oval track engine I've ever had was cast rods.

The junkyard ones with a good top end would usually spin rod bearings, not because the rods failed, but because they needed more oil clearance. When I started opening up bearing clearances is when the spun rod bearing stopped. My theory is with a huge rod journal heat builds and the bearing grabs the crank. With extra clearance the oil is able to keep everything cooler so the journals don't grow as much and the bearing never touches the crank journals. Right or wrong the extra oil clearance has helped longevity tremendously.

Same goes for street engines I have a 455 that I built that had stock factory pistons rods and rod bolts. It has plenty of clearance on the bearings, and has thousands of hard street miles on it, it's been flawless and I put it together in 1988. It will get pulled down to check it, but likely will go back together to go into another street car.

I've never used the early rubber rod in anything I've built, or junkyard engines, but I've seen the supposed weak cast rod take way more abuse than anyone thinks they can. They are made from steel, not china or glass............LOL
Same material that 90% of the still running Pontiac cranks are made from.

One other thing is the 67 and later cast rods have a stiffening riser on the big end that the earlier rods don't have, I assume the engineers put that in for a reason. I always use the later rods if I have a choice.

Today I'd spring for forged rods, but back in the day no one I knew, or hung out with had enough bucks to spend for forged rods, so we used what was available. A set of forged rods back then was twice what we spent on the whole engine to build it. Sometimes we would actually resize the rods and put better bolts in them, depended of the state of the budget and how busy the machine shop was at the time, as well as time frame to get it back up and running. Weekly dirt track shows don't give you much time to wait on the machine shop.

[Skip Fix]

In the late 80s early 90s when we had no good forged rods Like Eagle,SCAT etc and there were only 455 SD, Carillo or Crower billets. Butler and Barney Moravits out of San Antonio used and sold lots of those early rods AFTER getting a re heat treat. I know Barney had a place in San Antonio that heat treated oil company tools he used, and I think supplied Butler.
That said before NHRA allowed aftermarket rods in Stock/Super Stock John Schloe in his 69 RAIV Bird and said he usually ran it out the back door at 7000 with cast rods!

[b-man]

Three engines all with untouched cast rods, one bracket race 455 along with 455 and 400 dash driver engines.

https://forums.maxperformanceinc.com...5&postcount=19

https://forums.maxperformanceinc.com...22&postcount=4

https://forums.maxperformanceinc.com...1&postcount=22

Only due to convenience and budget was I running cast rods. The bracket race 455 was supposed to be a one season only temporary engine that ended up running so good that I left it in for over a decade of racing.

The forged Crowerods that I had purchased in the early ‘90s to build my bracket race 455 were used for a short time in that 455 which had block machining issues causing thrust bearing failure. The Crowerods sat patiently waiting until 2015 when they ended up in my 421 HO engine. The 421 is essentially a stock restoration with internal upgrades.

https://forums.maxperformanceinc.com...d.php?t=771742

If I’m investing 6 to 12k in a decent Pontiac engine no way am I using cast rods in it, wasting money rebuilding cast rods is a fools errand in my opinion.

The money spent on heat treating and rebuilding the early forged rods will probably exceed or at least equal the cost of decent new offshore forgings. You won’t end up with a better rod starting with the early forgings.

[Jay S]

You can compare the factory rods in this photo I took some years ago, left is an early rubber rod, middle is a late cast, far right is a mid 70s SD rod. There isn’t much strength where the I beam attached to the rod throw or the cap on the early rods, both are pretty thin. The cast rods are stronger, beefier in the places the need strength, and also weigh more. Either would work fine for a stockish street engine on a budget. I don’t think ARP bolts would add any strength to the early forged rod at all.

I built dirt track Pontiac’s with both the early forged, and the later cast rods in 455s. Usually held the RPM’s to 5000 maybe 5500 on most nights. We ran the early rods in a 455 for a full season. Midway thru the next season we had a night 3 rods decided they didn’t want to be attached the crank anymore. Amazingly it still drove onto the trailer (on 5 cylinders) and didn’t hurt the block. Maybe that says how soft the metal in those rods is though, and it failed rather spectacularly.

I have a friend with cast rods in a 455 hitting it with a 100 HP shot of NOS.

All Jim Hand ever ran in his 11 second 455 power wagon was stock cast rods. He even broke one crank, but to my knowledge never had an issue with the stock rods.

[mgarblik]

I have always felt you need to look at the connecting rods as a "system". The rods, the piston weight, fasteners and the machining accuracy Each of these components can make or break the "system". That's why some of us have had luck racing inferior parts, like myself without "system failure". In the 1980's. I ran the rubber rods, with lighter than stock pistons, superior fasteners, and perfect machining and balance at 6000-6200 RPM for hundreds of runs without a rod failure in a 421 in NMCA stock class. Lucky?, Probably. But that was the best available to those of us without a huge budget. Building an engine today, on a budget, I would use the best off shore aftermarket rod I could afford. Probably Molnar. If using Eagle or a no-name generic Chinese rod, the quality of the machining process becomes much more important to the "system". Every dimension needs to be verified and even today, every Eagle set of 8 rods I see need at least some re-machining to the big or small ends for size, out of round or taper. Just part of the build process. At the RPM range most of our Pontiac street engines run, connecting rod material and forged vs cast is a much less important part of the "system" than the quality of the finished machined part.

[Green Elephant]

I plan to use the Eagle rods I have for this build, but I might attempt to heat treat this set of early forged rods and see how they turn out.
I can heat treat steel and aluminum at work and my manager doesn’t mind us doing personal projects so it would be easy enough to accomplish if I can nail down the exact process for that steel. I believe they are made from 1140. If successful, I would add ARP bolts and have them machined to restore any dimensional problems.

[turbo69bird]

Pontiac made the early SD rods in batches of 2000 for certain performance dealers in 68-69-70 for their race cars

[steve25]

The early non SD standard production forged rods are not of a grade of steel where applying a heat treating process is going to gain you much for the effort and then the money involved in resizing them.

1140 steel is like the average hardware store 8”” adjustable wrench .

BTDT!

I would much sooner polish them , lighten them at the pin end and then spend money on cryo treating them without the new rod bolts in, then load in the new bolts and check & resize as needed.

[turbo69bird]

Originally Posted by turbo69bird

Pontiac made the early SD rods in batches of 2500 for certain performance dealers in 68-69-70 for their race cars

Here’s the info on that it’s just cool info that many didn’t know happened.

[HWYSTR455]

I use to use rebuilt factory rods with pretty good results, never had a rod let go.

I had a build that used the good 62-63 SD rods, and that was the only rod failure I've ever had. And they were well prepped.

With all the offerings these days, it really doesn't make sense to try or need to use 'old' OE rods.


.