Forged vs. Cast Con Rods

[John C.]

This isn't specific to Corvettes but I have great faith that someone knows the answers to the following:

Are cast connecting rods still in use today? I believe virtually all connecting rods are forged and have been for some time.

Are powdered metal rods forged? Sounds like a stupid question but I believe they are, it's just a different type of metal.

Are cracked cap rods the norm for today's engines? I read about this innovation some years ago (early 90's) but I don't believe they are more common than the standard machined rod caps.

My thanks to those that respond!

[Clem Z.]

Re: Forged vs. Cast Con Rods

GM uses cracked cap PM rods in most all their engines. all corvette engines since the LT-1 have used PM rods. they are even used in the ASA racing engines which are LS-1 corvette engines with a cam and oil system change. GM says these rods are good up to 500 HP. these PM rod have been test at GM in a 550 HP engine running at 6000 RPM for 72 hours.

[Clem Z.]

correction it was 45 hour test

i am trying to remember too many facts and my memory bank is getting confused

[Duke W.]

Re: Forged vs. Cast Con Rods

I don't know of any automotive applications that used cast rods - maybe some really old engines. Forged rods were pretty much the norm for automotive use in the post war era, but as Clem says, the powdered metal cracked rods have become the norm for new Chevrolet engines.

The first use of this technology that I am aware of is the Porsche 928 V-8 circa 1978.

Duke

[John C.]

Re: Forged vs. Cast Con Rods

Back to my stupid question: powdered metal is still a forging or is this some new process?

[John C.]

Re: Forged vs. Cast Con Rods

Found an answer using google

http://www.cartech.com/epg_parmatech/index.html

Powdered metal is metal injection into a mold, much like plastic injection molding.

Thanks Clem and Duke!

[Clem Z.]

Re: Forged vs. Cast Con Rods

duke some pontiac engines used cast conn rods and i think some buicks and olds also.

[Clem Z.]

Re: Forged vs. Cast Con Rods

the PM rods are so accurate they require no balancing after manufacture which i am sure saves money. the big disadvantage is they can not be reconditioned because of the cracked cap deal,if they are out of round on the big end you just ****can them. they are dirt cheap new,5.7 chevy PM rods are $250 for 8

[John C.]

Re: Forged vs. Cast Con Rods

I assume none of the techniques used to enhance forged rods, e.g., side beam polishing, shotpeening, are necessary (maybe not even desirable?) with PM rods?

[Clem Z.]

Re: Forged vs. Cast Con Rods

correct

[Dave Suesz]

Not so new...

Powdered metal has been around for decades. Literally, metal powder is poured into a die, and compressed into a precision part, which has about "0" strength. The parts are then placed in an oven, and sintered, which heats them almost to the melting point, and carefully cooled to produce a strong, precision part with little or no machining. A very common application of this process is bronze bushings, such as pilot bushings for the transmission input shaft.

[Gerry Proctor]

Re: Forged vs. Cast Con Rods

For sure, Pontiac V8 rods made from 59 and on were cast Armasteel except for the SD and HD, Clem. Can't say absolutely for sure that no Olds or Buick but none were cast in the 60s and on. Pontiac was a bit of a lone wolf with the cast rods. No other corporation (Ford, Chrysler...even AMC) saw any merit in a cast rod.

[Craig S.]

Re: Forged vs. Cast Con Rods

They sound pretty stout...so are they still less overkill than a good grade forged rod? How do they crack the cap and form the split, is this before the sintering process? It sounds like this is more of a production aid for uniformity and simplicity that an actual superior process/product than the older forged rods. Is that the case?...thx, Craig

[Duke W.]

Re: Forged vs. Cast Con Rods

For volume production powdered metal rods appear to be gaining favor, probably due to less machining and lower unit cost. The rods are built as one piece, then "split" in a hydraulic fixture to separate the cap from the rod. The parting line is in the correct position everytime due to notches that create a stress concentration and a uniform application of the force that breaks them.

Duke

[Craig S.]

Re: Forged vs. Cast Con Rods

Thx Duke!...Craig