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would it be possible to run aluminum rods for short distances on the street say 10 miles or so? School me on who's correct and why.

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10 miles is a STREET CAR ? ..

HOPPING ON 95 and driving to FL from MD is a STREET CAR ...IMHO !

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Yea you just don't beat on them till there up to temp.

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Do you see any of thr Pro teams, fuel or Pro Stock, blown alcohol or Comp Elininator teams wait to race thier motors until the rods are up to temp? I'm almost positive that there are road race motors as well as circle track motors that use and race aluminum rods that beat on them as soon as they get them on the track without warming up the oil Maybe not

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It has nothing to do with temperature.

It is all about fatigue life. Let's take steel for an example. As steel goes through millions of tension/compression cycles its strength goes down. At some point the strength levels out, IIRC at about 57% of new. Then the curve of strength vs. cycles is flat.
Now let's look at aluminum. As the cycles mount up the strength goes down...and down...and down. The curve never levels off. It continues until it hits zero. By that time your aluminum part has long since broken. Sounds bad, doesn't it?
But there is a question. How come some aluminum parts last longer than we would expect? I think it has to do with the amount of cyclic stress to which the aluminum part is subjected. Maybe the curve becomes less steep if the part is only stressed to, say, 50% of yield or ultimate. Then the acceptable service life would be extended past the time that an overhaul was needed.

Does anyone have any references for this?

R.

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IIRC, in order for the part to fatigue, it has to be loaded (stressed) above the fatigue strength. If the rods are designed so that at a given bobweight and RPM limit, no section is loaded beyond the fatigue strength rating, they'll theoretically last forever in that application. Big question is, how sure can you be that you're under the fatigue strength???

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No. As the aluminum part fatigues the strength keeps going down as the number of cycles goes up. It eventually goes to zero.

What you are describing is for steel, where it levels out at some point.

That's why people don't worry so much about steel connecting rods.

But I'm not sure if a cycle at say 10% of the new tensile stress is the same as a cycle at 90% of the new tensile stress. I am looking for that answer. A lot of this metallurgical stuff isn't "logical" unless you're a metallurgist.

Briggs&Stratton engines use aluminum connecting rods.

Suppose your part will break at 10 million cycles. How many miles is that?Let's use a 27" tire and 3.91 gears. Assume all of the mileage is in High gear. So you have 2,921 revolutions per mile at the crankshaft. How does 3,423.9 miles sound?

I'm back to liking steel rods more and more.

R.

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