Powder forged rods, good read on strength strong

[Joseph Upson]

Apples and oranges. Even if the total HP output of both engines were the same, loading per rod is completely different.

Yes, but the metal used is the same, and physical characteristics should favor increase in strength as rod length shortens given the same diametrical area being compressed and stretched over the rotating cycle due to reduced length being more rigid and less likely to bend on compression and less likely to stretch from the reduced weight at the top of the stroke.

I'm addressing the new rod material vs. old, not the LS1 and V6 rods themselves.

That might be the crucial element in the LS1 rod complaints since they were produced in 6.098 and 6.125 lengths if I recall correctly depending on the year/engine.

[sprucegagt]

I'm addressing the new rod material vs. old, not the LS1 and V6 rods themselves.

I agree with the new material/rod length strength statement. But that's not what this is about.

I can't find the thread anymore but iirc they were saying that the rods were failing above 6K RPM..

hmmm, 60 degree rods aren't.

That's all about an RPM limit.

[Joseph Upson]

I agree with the new material/rod length strength statement. But that's not what this is about.





That's all about an RPM limit.

Hince the importance of a stronger rod material to help sustain that, you can set the rpm limit to whatever you want, whether the rod is strong enough to handle it is independent of your setting. It's the same difference, whether you express rpm limits in terms of rod strength, or rod strength in terms of rpm limits. It appears some LS1 rods are not strong enough to handle much above 6k which is still much higher than its production predecessors were spinning and making less power.

Who knows what we are actually dealing with given GM doesn't tell everything and what they have posted is sometimes in accurate like the alleged 5.9" rod that is actually 5.827".

[Barry]

If I could of removed my rev limiter I could of found the mechanical limits of my 3100 rods before I yanked it out.

[torq455]

less hp, more rods, blah. you also have to consider stroke and bore sizes and over weight.

[Monzsta]

If I could of removed my rev limiter I could of found the mechanical limits of my 3100 rods before I yanked it out.

I tried that with mine. It simply wouldn't rev past 6600. Even in neautral.

[Joseph Upson]

less hp, more rods, blah. you also have to consider stroke and bore sizes and over weight.

This is about stock equipment durability, so that stuff is not as important since we're not talking about the addition of larger pistons and weight changes that result, further more the big end of the rod and the small end diameters are increased relative to the early 5.7" rod diameters.

The significance of that is the reduced rod material length between the center to center point of the big end and small end that results from the simultaneous changes, which means less weight to contribute to tensile load via a relatively shorter rod due to some of it being exchanged for increased crank and piston pin diameters in the same way you trade off tire side wall for increased rim diameter but retain the same overall assembly diameter. We have agreed that the shorter rod tends to be stronger due to increased rigidity.

In other words: If the distance from the top of the circle of the big end of the rod to the bottom of the circle of the little end of the rod is reduced, you stand to gain strength especially against compression forces where added length can increase the risk of bending and stretching under load.

My calculations show the following:

Actual rod length center to center = 5.827" which is .127" longer than the 5.7" rod.
Actual metal length increase between those points after deduction of piston and crank pin diameter increase:

.127 length increase - (.0178 pin radius increase + .125 crnk pin radius increase) = .0158"

So a .016" length increase instead of the entire .127" increase in length. The piston pin weight maybe the same, more, or less since it is also treated for strength (I forgot with what method).

Regardless, using the LS1 rod made from the same material as an examplary strength measure is still reasonable although not perfect since it is considerably longer, and lets face it, there is no real rod or crank failure history with the later design V6 engines up to the levels they are being pushed now or before.