They are more finished now, just the final touch... and lighter still! :)
http://forums.pelicanparts.com/uploa...1606684225.jpg
http://forums.pelicanparts.com/uploa...1606684225.jpg

But I'm actually considering putting them on the shelf now, because I're leaning towards bigger and stronger ... (when do I learn) :rolleyes:

One needs to be careful when considering what Porsche did with its race engines. One approach was to make them just strong enough to last one race, which by and large is not something which will work for most of us.

Here is a Gen 4 LS Chevy rod that people run over 1000hp and 7000rpm with a 105mm (495g + 145g pin) and 92mm stroke. All the LS family run a 6.1in rod for a 1.7 rod/stroke ratio on the 6.0/6.2. Energy the rod has to take from RPM is E=mv^2 so the Chevy rods are taking MUCH more stress even at 400hp then any 7000rpm 911 motor.

Needless to say, stock 911 rods are damn near indestructible. The much thinner 993/996Turbo rods don’t bend until 600+hp.

http://forums.pelicanparts.com/uploa...1606799227.jpg

You are right, the rod is showing stresses in compression which is usually not a problem for a rod to handle unless its very high boost and high cylinder pressures. Whats critical for a NA engine are stresses in pulling direction which where it will come apart at high revs.

Regarding the rod bolt, the plot is showing deflection under tension.. so not really saying anything. The stresses are of course highest in the neck down area

With this discussion I think an intuitive explanation of why shot peening works would be a big help.

A crack requires a place to start. If it can't start it won't crack. Cracks will always start at the surface. ("The surface" includes the surface of voids and other internal defects but those are exceptions, especially on forged parts.)
So anything you can do to make it harder for that first hint of a crack to start on the surface you can significantly reduce cracking. Most treatments to increase the durability of parts come down simply to making the surface compressed. Nitriding and other hardening treatments change the surface chemistry by forcing atoms into the alloy's crystalline matrix that make the molecules want to be slightly bigger. This makes them "chemically compressed". Shot peening compresses the surface by striking it to plastically deform the surface so it is physically compressed.

And here we get to the simple reason these methods work. When you start to stretch the metal the compressed surface isn't stretching, it is just becoming uncompressed. You can put a lot of stress into the part and the surface is just becoming 'relaxed'. You have to stress the part a lot more to get it to the point where the surface is starting to come under tension and until you get to the point where the surface exceeds the limits of elastic deformation where you will start fatiguing the part because the crack must start on the surface.

Polishing will increase the fatigue resistance of a part by removing surface variations that provide a starting point for cracks but it is not anywhere near as effective as shot peening or a surface treatment like nitriding. That is why there is a milspec for shot peening but not for just polishing a part. If you polish a part and then shot peen (or nitride it) it you probably will increase its fatigue resistance beyond a simple surface treatment but it will get expensive in a hurry.

I had a set of 2.7 rods shot-peened in 1985. Also balanced and crack tested.

Built it as a 2.8.

Those rods go to 8000 RPM on every shift from 1990 up to today!

I'll admit that luck might be part of the equation.

Brookfield Engine Builders baby!

2.7 rods are quite capable of 8,000 rpm as they are. The main reason to use something else on motors of this era is to lose weight. Maybe they get marginal at 9K, but my 2.7 needed to be shifted below 8K to optimize accelleration, but would easily stretch to 8 (I'd been shifting at about 8,200 before I dynoed the motor and realized I was better off at 7,600) depending on the track.