SBC rod question

[MadBill]

Or, run a few samples of each to failure in a fatigue tester at different stress levels and see if you get the same results that GM clams...

[MELWAY]

Seems like the best bang for buck. Are scat I beams...

How hard have people run these and if they have failed where did they give up?

[rfoll]

There was a post on here a few years ago where a builder was using the Scat 3/8" cap screw rods on a 500 HP plus engine. When he freshened up the engine after a season or two, he found out the customer was hitting the motor with something like 200HP of nitrous.

[pdq67]

"This was the same engine that had a dealer installed "fitted block" because of antifreeze damage."

Years ago one of APGreens Ford 6-wheeler trucks lost the piston pin keepers and scored a cylinder. We had it replaced and I thought it funny that the remanufactured block still had a stock bore until we took it out on the road and it started leaking antifreeze behind the bell housing. Turned out the 361" FE V-8 had a casting flaw that was thin and had ever so slightly cracked from brand new! Well a rebuilt 391 FE V-8 replaced it fine!

Shit happens.

pdq67

[bigfoot]

Broke a eagle rod I beam..in a 2 year old oval track motor..2 barrel 375 hp...over revered when back tires jacked up...can I just change one or buy a set of new stronger rods ?

[wyrmrider]

yes

[stealth]

Excerpt from quoted analysis:
https://www.forging.org/system/files/fi ... havior.pdf

A primary design criterion for the connecting rod is endurance limit. Failures of
connecting rods are often caused by axial and bending loads acting perpendicular to the
axes of the two bearings. Typical fracture locations of the powder metal rods are near the
wristpin and crank pin end bores, while typical forged steel rod fracture is in the I-beam
section. The typical density of powder metal connecting rod is 7.85 g/cm3. Powder metal
connecting rods show porosity, oxide penetration, decarburization or other defects, which
is typical of powder metal material. The depth of decarburization should not exceed 0.4
mm. Shot peening with optimum peening intensity improve fatigue strength by 27%.
Over peening can form cracks at the surface of the connecting rod. Majority of the fatigue
cracks start subsurface, due to compressive residual stress induced by shot peening. In
powder metal connecting rods, shot peening removes the oxides on the rod surface, but the oxides entrapped in the channels and pores, below the surface remain, causing the crack to originate below the surface


Seems like an odd material to use for a connecting rod, unless cost (much less labor in machining) is your primary objective. Just something to consider.....

[pdq67]

"Seems like an odd material to use for a connecting rod, unless cost (much less labor in machining) is your primary objective. Just something to consider....."

That's just why they started making PM rods!! And everything else.

I learned about PM parts back in '65 because I blew the spider gears out of my Mom's new '65 Custom 300 Chevelle 195hp/283, 3-speed 4-dr. because I was dragging it at night and was running recap 8.00/14 "REAL" slicks on it! Made a U-turn to come back and the damned PM spider gears broke!! Our Mechanic clued me in on what happened because Mom's 283 didn't have enough power to hurt anything!!

pdq67

[turbo camino]

(sorry for the necromancy, I blame that dang 'similar topics' box at the bottom of every page...)

I think the assumption is that the PM rods would be brittle - I'm not sure that's correct.

These are (were?) L31 PM rods. I think the story was something about a wastegate problem and a boost spike of 40+psi.