CarsByCarl said:There has been some talk lately about how stock rods compare to some of the 5140 rods on the market. I don't have any Eagle SIR rods on hand, but I do have some some RPM 5140 rods, so I took a few pictures to show the differences. The RPM rods in these pictures are 6.800 stroker versions with 2.2 journals, but the 6.605 versions are built very much the same.
Overall view of the two rods side by side. Notice the difference in the thickness of the material around the big end. Also notice that the RPM rods have 7/16" ARP bolts vs. the stocker's 3/8". While the RPM beam is narrower in width, it is about .060 thicker across the webbing.
Close-up of the small end. Again notice the thickness of material around the pin as well as the width.
DaveMcLain said:Here are a few pictures of the Eagle SIR rod that I had fail in a 460. I posted a description of this problem in a previous post but I didn't take any pictures. Here they are in all their gory detail:
Notice how the rod completely failed in the beam yet the big and small end were totally intact and undamaged. Bearings, rod journal, wrist pin etc all looked great. These rods were run in a 460 that was only ever turned a maximum of 6500rpm and when run in the application 6200rpm. Admittedly the KB 137 is not a light piston but the rpm level wasn't that high either. Engine horsepower was 585 and the engine ran a best et of 6.50 at 100 mph in the 1/8th mile in a 1962 Ford pickup. This was Wes Littrell's cousin Shannon's truck that was at the bash a few years ago.
These rods were used in the 460 I built for the Engine Masters' Challenge back in '03 so they probably had around 100 dyno pulls and probably 40-50 drag racing passes total.
While it's difficult to tell from the pictures it seems as though the RPM rod has possibly a bit more "beef" in the beam. This is the problem area on the SIR rods of the design that failed but I've also heard that Eagle has improved this design within the last couple of years, is this true?
tiger said:How wide and how thick is the beam on the eagle compared to the rpm? I can measure my set of Eagle's when I get home if someone does not beat me to it.
CarsByCarl said:Looks like the SIR snapped up near the pin first. The RPM rod is a little more beefy up there, and so are the new Ford rods. Did Eagle make a change there too?
DaveMcLain said:It's tough to say. I do know that in this failure the starter was knocked off of the engine going 100mph and lost! The engine was still running and the truck was driven back to the pits. So this means that the section of the rod that was banging around was at least pretty much longer than it is now for a while anyway. It was at least long enough to come through the pan and pan rail and hit the starter motor with enough force to break it off of the end piece.
I had an SIR rod fail in a small Chevy engine too however and that one must have broken nearer to the big end because it didn't do much damage at all inside of the engine. It didn't even hit the cam on a 400!
CarsByCarl said:Found a picture of the 6.605 RPM rod:
Ok, let's play nice now.DaveMcLain said:That rod looks to have more material around the big end and possibly the small end too. But in both of the failures that I've had those areas of the rod were just fine. I'd say that if that rod has a similar cross section in the beam failures WILL occur, sooner or later and probably sooner with a typical weight piston and pin even at very moderate rpm and power levels.