Service Life of Steel H-Beam Rods

[lekid]

Wondering what the service life of a steel H-Beam connecting rod would be? My current rods are old!!! Makes me wonder if I am not playing with fire still running them. They are 14 years old. The first 8 years, the engine made around 750hp (500hp N/A + 200-250hp of nitrous) with around 3,000 miles of street driving and around 600-650 1/4 mile runs. Then the engine was upgraded, rods inspected and bolts upgraded to ARP2000. The engine then made progressively 950hp up to today's 1150hp on nitrous and another 200-250ish 1/8 mile runs.

I feel like I am pushing it! If it means anything, the rods are Eagle 4340 H-Beams. We have a new set of K1 H-Beam with ARP2000 on hand.

I am being told to not overthink it and continue running them and at the same time being told to put the new K1 in since they have had no run time, have new rod bolts and are a better rod than the Eagle all together.

Welcoming your opinions!

[ptuomov]

One school of thought is that the remaining life expectancy of steel rods is proportional to the time that they’ve been already run...

[Powertrip]

This is a No Brainer! You have on hand brand new, better rods, use them and sleep better.
Sell the old rods to the guys telling you to not over think it.

[GRTfast]

Below a certain critical stress value, the fatigue life of steel is “infinite”. The answer to your question is proportional to the stress they see in operation.

[ptuomov]

How many rod failures are caused by improper installation? Or minor manufacturing defects? Compare that to the failure rates from fatigue.

I’m personally running 32 year old and 100,000+ miles used sintered steel stock rods in an engine that is making 3x the stock power. As long as oiling is working, they are holding up fine, in fact better than the aftermarket “performance” rods in other people's engines.

[Alaskaracer]

I had steel H-beam rods in my last engine. Was making a bit over 1100 hp. Those rods had been in three different engines, several different power levels. They had been given new rod bolts twice, new pin bushings twice, and resized twice. When I finally kicked out a pair of them and killed my engine, it wasn't from power, rpm (I was turning 8000-8200) or age....lost oil delivery to that journal, bearing welded and spun, rods went with them.....

My guess is if they hadn't failed due to killing a rod bearing, I'd still be running them.....I just never did figure out why I lost oil to that journal....

[bob460]

What cid is it? and what rpm you turning ?

[Alaskaracer]

What cid is it? and what rpm you turning ?

Me? Last engine with those rods was a 604" 12* BBC. Turned about 8200 on the top end

[bob460]

What cid is it? and what rpm you turning ?

Me? Last engine with those rods was a 604" 12* BBC. Turned about 8200 on the top end

No the OP my bad, but how many runs did you put on your rods?

[Alaskaracer]

No the OP my bad, but how many runs did you put on your rods?

I can't even begin to tell you...I know more than 1000 before I ended up with them, and I ran them at least another 500 or more......

[steve316]

you hear a lot of racers telling you how many passes they have on their rods. I buy the best rods I can afford and change them at a predetermined number of passes. If something breaks in the engine other than the rods, then you have to make a judgement call on them as well. That is what you need to do now, replace the rods or everything in the motor. I remember Larry Morgan saying in interview that if they blew up a motor with steel rods they may be able to salvage the valve covers. Good luck with your decision.

[lekid]

409 SBC (4.165x3.750) and it sees 7600-7800rpm max

[ptuomov]

Below a certain critical stress value, the fatigue life of steel is “infinite”. The answer to your question is proportional to the stress they see in operation.

This makes a ton of sense to me.

Is the conclusion then:

If the stress is below that limit, never replace steel rods unless there’s a specific reason.

If the stress is above that limit, have a schedule by which the steel rods will be replaced. But this leads to the question why to use steel rods in the first place in the application, rules?

I’m asking, not telling. Does this make sense?

[GRTfast]

Below a certain critical stress value, the fatigue life of steel is “infinite”. The answer to your question is proportional to the stress they see in operation.

This makes a ton of sense to me.

Is the conclusion then:

If the stress is below that limit, never replace steel rods unless there’s a specific reason.

Yes. The kicker is, how well does one understand the actual stress state a rod is subjected to?

[ptuomov]

Below a certain critical stress value, the fatigue life of steel is “infinite”. The answer to your question is proportional to the stress they see in operation.

This makes a ton of sense to me.

Is the conclusion then:

If the stress is below that limit, never replace steel rods unless there’s a specific reason.

Yes. The kicker is, how well does one understand the actual stress state a rod is subjected to?

Since it’s mostly an issue of tension, isn’t that a mass vs cross-sectional area vs. acceleration computation? In any case, you’d think that the rod manufacturer can compute the number given the component weights, geometry, and engine speed?