SBC rod question

[scotts439]

Which is stronger.... stock forged steel SBC rods or the later PM rods? for arguments sake, both have good aftermarket bolts.

[mag2555]

Stronger over what time frame of useage?
If we are taking even just one full race season at 7k RPM , give me the steel rods !!!

[pamotorman]

these are the PM rods used in the 2015 650 HP supercharged ZO-6 corvette engine Lightweight, high-strength powder-metal steel connecting rod design for reduced reciprocating mass and quicker rev capability. It has the same balance mass as the LT1 rod, but a higher load capability, with features including machined lightening slots and additional lightening features, as well as a “stepped”/wide pin end with a premium bushing.

[pdq67]

Take one rod of each type, put them in an old Blacksmith "post-vice" and hit each several times with a 10 pound sledge, (full swings), and see which one bends and which one breaks??

Use the rod that bends, imho..

pdq67

[Dan Timberlake]

Chevy claims the 10108688 PM rods are better than pink rods.
https://sdparts.com/details/gm-performa ... s/12495071
If this picture is correct, the Pm replacement still uses through bolts and the straight across notch for the bolt head. Too bad.

Most of the cracks I ever saw in through bolt con rods originated from the bolt head notch. Straight across notch ala Chevy and Mopar and others is pretty poor. A few started at surface damage on the beam or under the pin eye.

The geometry of a nutless design with the rod tapped is (by inspection) WAY better (lower stress concentration) than the straight-across notch for the bolt head.

I highly value ductile parts (elongation over 8%) when my butt is astride/aboard going down the road or through the woods.\
But I would choose low stress geometry and good fatigue strength first for con rods.

And. mag particle inspection, careful surface prep and look into getting any rod shot peened.

Here is some college kid's thesis on Fatigue life of "both" types of con rods. It seems to have the blessing from the American and Steel Institute.
https://www.forging.org/system/files/fi ... havior.pdf

On page 40 he references some paper by some guy from Ford Motor, Scientific Research Laboratories. Chernenkoff, R. A., “The effects of surface modification on the fatigue performance of powder-forged steel,” Ford Motor, Scientific Research Laboratories.

Student says - "Shot peening of connecting rod has the biggest impact on the fatigue life. The effect of shotpeening on PF material used for connecting rod is
described by Chernenkoff et al. (1995). They further explained the process parameters for precision peening. These include shot diameter, shot distribution, shot shape, shot
hardness, shot type, shot density, shot impact angle, shot flow rate, shot blast pattern, nozzle-workpiece position relationship, and exposure time. Comparisons of shot peened
and unpeened specimens were conducted and was found that the fatigue strength increases from 262 MPa for unpeened specimens to approximately 407 MPa for peened
specimens at 20A. "

Improved fatigue life is what we are chasing by modifying rod geometry and fancy materials.
Note in that Chernenkoff test peening provided a 50% improvement with the same danged part. That means if the rod had an infinite life at some rpm, the simple act of MIL spec peening would theoretically raise the safe rpm limit 20% . Not bad. Not bad at all.

[racear2865]

Chevy claims the 10108688 PM rods are better than pink rods.
https://sdparts.com/details/gm-performa ... s/12495071
If this picture is correct, the Pm replacement still uses through bolts and the straight across notch for the bolt head. Too bad.

Most of the cracks I ever saw in through bolt con rods originated from the bolt head notch. Straight across notch ala Chevy and Mopar and others is pretty poor. A few started at surface damage on the beam or under the pin eye.

The geometry of a nutless design with the rod tapped is (by inspection) WAY better (lower stress concentration) than the straight-across notch for the bolt head.

I highly value ductile parts (elongation over 8%) when my butt is astride/aboard going down the road or through the woods.\
But I would choose low stress geometry and good fatigue strength first for con rods.

And. mag particle inspection, careful surface prep and look into getting any rod shot peened.

Here is some college kid's thesis on Fatigue life of "both" types of con rods. It seems to have the blessing from the American and Steel Institute.
https://www.forging.org/system/files/fi ... havior.pdf

On page 40 he references some paper by some guy from Ford Motor, Scientific Research Laboratories. Chernenkoff, R. A., “The effects of surface modification on the fatigue performance of powder-forged steel,” Ford Motor, Scientific Research Laboratories.

Student says - "Shot peening of connecting rod has the biggest impact on the fatigue life. The effect of shotpeening on PF material used for connecting rod is
described by Chernenkoff et al. (1995). They further explained the process parameters for precision peening. These include shot diameter, shot distribution, shot shape, shot
hardness, shot type, shot density, shot impact angle, shot flow rate, shot blast pattern, nozzle-workpiece position relationship, and exposure time. Comparisons of shot peened
and unpeened specimens were conducted and was found that the fatigue strength increases from 262 MPa for unpeened specimens to approximately 407 MPa for peened
specimens at 20A. "

Improved fatigue life is what we are chasing by modifying rod geometry and fancy materials.
Note in that Chernenkoff test peening provided a 50% improvement with the same danged part. That means if the rod had an infinite life at some rpm, the simple act of MIL spec peening would theoretically raise the safe rpm limit 20% . Not bad. Not bad at all.

Shucks, I knew all that... hehe
reed

[Kevin Johnson]

Here is some college kid's thesis on Fatigue life of "both" types of con rods. It seems to have the blessing from the American and Steel Institute.
https://www.forging.org/system/files/fi ... havior.pdf

SAE paper, published prior to thesis:
http://www.eng.utoledo.edu/mime/faculty ... 1-1529.pdf

I would also characterize the inertial forces in tension on the cap and big end as bending forces.

[Krooser]

There are a lot of PM rods being used on the dirt tracks here in WISSOTA land… street stocks, B-mds, super stocks. Usually 450 HP and less… cheap, reliable and plentiful I bought 17 rods for $60.00 for my son's modified engine. They are really close on weight… all were 595-601 grams with most right at 600. GM sez the rod bolts are good, too but our engine guy changed 'em for ARP's.

[pamotorman]

Chevy claims the 10108688 PM rods are better than pink rods.
https://sdparts.com/details/gm-performa ... s/12495071
If this picture is correct, the Pm replacement still uses through bolts and the straight across notch for the bolt head. Too bad.

Most of the cracks I ever saw in through bolt con rods originated from the bolt head notch. Straight across notch ala Chevy and Mopar and others is pretty poor. A few started at surface damage on the beam or under the pin eye.

The geometry of a nutless design with the rod tapped is (by inspection) WAY better (lower stress concentration) than the straight-across notch for the bolt head.

I highly value ductile parts (elongation over 8%) when my butt is astride/aboard going down the road or through the woods.\
But I would choose low stress geometry and good fatigue strength first for con rods.

And. mag particle inspection, careful surface prep and look into getting any rod shot peened.

Here is some college kid's thesis on Fatigue life of "both" types of con rods. It seems to have the blessing from the American and Steel Institute.
https://www.forging.org/system/files/fi ... havior.pdf

On page 40 he references some paper by some guy from Ford Motor, Scientific Research Laboratories. Chernenkoff, R. A., “The effects of surface modification on the fatigue performance of powder-forged steel,” Ford Motor, Scientific Research Laboratories.

Student says - "Shot peening of connecting rod has the biggest impact on the fatigue life. The effect of shotpeening on PF material used for connecting rod is
described by Chernenkoff et al. (1995). They further explained the process parameters for precision peening. These include shot diameter, shot distribution, shot shape, shot
hardness, shot type, shot density, shot impact angle, shot flow rate, shot blast pattern, nozzle-workpiece position relationship, and exposure time. Comparisons of shot peened
and unpeened specimens were conducted and was found that the fatigue strength increases from 262 MPa for unpeened specimens to approximately 407 MPa for peened
specimens at 20A. "

Improved fatigue life is what we are chasing by modifying rod geometry and fancy materials.
Note in that Chernenkoff test peening provided a 50% improvement with the same danged part. That means if the rod had an infinite life at some rpm, the simple act of MIL spec peening would theoretically raise the safe rpm limit 20% . Not bad. Not bad at all.

when I used stock chevy rods with thru bolts I polished the area where the head of the rod bolt set to remove the machine marks

[bigjoe1]

Little known FACT--- The famous PINK RODS are exactly the same as any other not pink rod, EXCEPT, the pink rod has been magnaflux tested.NO OTHER DIFFERENCE at all.


JOE SHERMAN RACING

[rob vine]

for the price of a set of rods ,, like scat i beam rod with cap screws and dowels and made of 4340 , its not worth it to use or recondition old rods and buy bolts ,, parts and labour and a few bucks more and you got 10x the rod

[mag2555]

The test between these two rods that I want to see the results of is one that is done on a detonating motor that is on the edge of loosing the grip / crush on the rod bearing!

[user-612937456]

Little known FACT--- The famous PINK RODS are exactly the same as any other not pink rod, EXCEPT, the pink rod has been magnaflux tested.NO OTHER DIFFERENCE at all.


JOE SHERMAN RACING

I read in either Hotrod or SC mag some years ago that the pink rods were select castings which probably meant they were probably magnifluxed like you say but that they were also shot peened?

I dont have an opinion on the PM rods just what I have read and heard that the PM rods are superior to the pink rods which isn't terribly strong they are supposed to be rated to stand 450+ HP sustained

Take one rod of each type, put them in an old Blacksmith "post-vice" and hit each several times with a 10 pound sledge, (full swings), and see which one bends and which one breaks??

Use the rod that bends, imho..

pdq67

I like your highly scientific laboratory old Blacksmith "post-vice" test LOL

[kirkwoodken]

When I attempted to blue print my second 1968 Z/28, two of the "Pink Rods" had lengthwise cracks in the pin area. Since they were supposed to be magged, I called a Chevy rep and was told lengthwise cracks/inclusions were not considered to be a problem or weakness. Another unwanted "learning experience". I replaced the two funny rods.

This was the same engine that had a dealer installed "fitted block" because of antifreeze damage. (I bought the car used.) Only problem was they used a 327 fitted block instead of a 302. Pistons were 1/8" in the hole. I would NEVER let a dealership work on any high performance vehicle.

[woody b]

The test between these two rods that I want to see the results of is one that is done on a detonating motor that is on the edge of loosing the grip / crush on the rod bearing!

Somebody needs to build an engine with 4 "pinks" and 4 PM rods. Put it on a dyno under a good load, crank the timing up to 50 or so, and see which rod comes out first.