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Rod strength

General engine tech -- Drag Racing to Circle Track

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mag2555
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Rod strength

Post by mag2555 » Mon Dec 02, 2019 6:50 am

If it only takes 1500 psi to crack these Rods in there thickest section, then how strong can these production Rods be?
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Circlotron
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Re: Rod strength

Post by Circlotron » Mon Dec 02, 2019 7:12 am

It says "1500 pounds" not 1500 psi. That 1500 pounds may be concentrated on an area way smaller than a square inch.

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Re: Rod strength

Post by Krooser » Mon Dec 02, 2019 7:44 am

Not to mention the design is likely favorable to the cracking process and, I would imagine, they use a tool designed to fracture the cap correctly.
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ptuomov
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Re: Rod strength

Post by ptuomov » Mon Dec 02, 2019 8:25 am

Doesn’t the area matter also, probably less than square inch?

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Re: Rod strength

Post by ptuomov » Mon Dec 02, 2019 10:17 am

ptuomov wrote:
Mon Dec 02, 2019 8:25 am
Doesn’t the area matter also, probably less than square inch?
Day late and dollar short on my part, point was made above...

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Re: Rod strength

Post by lefty o » Mon Dec 02, 2019 11:22 am

rod being strong where they crack the cap, does not dictate rod strength as most would view it.

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Re: Rod strength

Post by PackardV8 » Mon Dec 02, 2019 12:35 pm

Rods are designed to be strongest longitudinally in tension and compression. In operation, there should never be any forces exerted perpendicularly, so strength in that axis is moot.
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Re: Rod strength

Post by Rick! » Mon Dec 02, 2019 1:54 pm

lefty o wrote:
Mon Dec 02, 2019 11:22 am
rod being strong where they crack the cap, does not dictate rod strength as most would view it.
^^This guy gets it. It's a manufacturing operation, not a strength test. A few years ago, cracked cap rods were popular.

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Re: Rod strength

Post by lefty o » Mon Dec 02, 2019 2:05 pm

Rick! wrote:
Mon Dec 02, 2019 1:54 pm
lefty o wrote:
Mon Dec 02, 2019 11:22 am
rod being strong where they crack the cap, does not dictate rod strength as most would view it.
^^This guy gets it. It's a manufacturing operation, not a strength test. A few years ago, cracked cap rods were popular.
packardV8 explained it better though.

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Re: Rod strength

Post by n2omike » Mon Dec 02, 2019 3:50 pm

The 306 in my mustang let go a couple weeks ago. Mexican block, Boss 302 crank, Boss 302 rods, Probe pistons... spun 7000 rpm over and over and over again on the street and at the track. At the track, it was always running off a 200 hp plate. Ran 6.26 @ 109 and 9.87 @ 135 with a toploader 4-speed, 4.33 rear and 28x9 tire.

Anyway, after tearing it down, it was a rod bolt that let go. No lack of oil, journal looks like it could be re-used, no spun bearings... just a rod splayed open like a rod bolt broke. Tore everything associated with the rear two cylinders all to pieces. What impressed me, was the adjoining rod! It got MANGLED... but never let go! It even took a HARD hit to a stress riser next to the bolt, and still stayed together. It's kind of ironic that 50 year old Ford parts were super heros... and the failure rested with a 3/8 ARP Wave-lock rod bolt. It was the standard black series, and had been in the engine around 15 years. I ran it for about 8 years, and refreshed it about 7-8 years ago. Oh well, engine owes me nothing! Just VERY impressed with those old Ford rods from 50 years ago!!!

Oh well... Finally time to put the 363 together. :)

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Re: Rod strength

Post by Schurkey » Mon Dec 02, 2019 4:14 pm

Have you ever "cut" glass? You scrape a line on it, and smack it. The scored line is a tremendous stress-riser, the glass breaks at the scored area.

Note the text that goes with the photo:
...the rods are cracked on a pre-scored line...

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Re: Rod strength

Post by digger » Mon Dec 02, 2019 4:20 pm

Schurkey wrote:
Mon Dec 02, 2019 4:14 pm
Have you ever "cut" glass? You scrape a line on it, and smack it. The scored line is a tremendous stress-riser, the glass breaks at the scored area.

Note the text that goes with the photo:
...the rods are cracked on a pre-scored line...
just don't ad any extra pre-scored lines and you are GTG

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Re: Rod strength

Post by Schurkey » Mon Dec 02, 2019 6:31 pm

digger wrote:
Mon Dec 02, 2019 4:20 pm
Just don't ad any extra pre-scored lines and you are GTG
Thus the admonition--back when people did such things--to always grind/sand/polish the rod beams lengthwise instead of crossways.

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Re: Rod strength

Post by exhaustgases » Mon Dec 02, 2019 6:46 pm

n2omike wrote:
Mon Dec 02, 2019 3:50 pm
The 306 in my mustang let go a couple weeks ago. Mexican block, Boss 302 crank, Boss 302 rods, Probe pistons... spun 7000 rpm over and over and over again on the street and at the track. At the track, it was always running off a 200 hp plate. Ran 6.26 @ 109 and 9.87 @ 135 with a toploader 4-speed, 4.33 rear and 28x9 tire.

Anyway, after tearing it down, it was a rod bolt that let go. No lack of oil, journal looks like it could be re-used, no spun bearings... just a rod splayed open like a rod bolt broke. Tore everything associated with the rear two cylinders all to pieces. What impressed me, was the adjoining rod! It got MANGLED... but never let go! It even took a HARD hit to a stress riser next to the bolt, and still stayed together. It's kind of ironic that 50 year old Ford parts were super heros... and the failure rested with a 3/8 ARP Wave-lock rod bolt. It was the standard black series, and had been in the engine around 15 years. I ran it for about 8 years, and refreshed it about 7-8 years ago. Oh well, engine owes me nothing! Just VERY impressed with those old Ford rods from 50 years ago!!!

Oh well... Finally time to put the 363 together. :)

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If it was a powder rod what would it have done?


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Re: Rod strength

Post by turbo camino » Mon Dec 02, 2019 7:17 pm

L31 powdered rods. Look how they shattered like glass! JUNK!
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DON'T PANIC

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