neilca; You're right and I'm -- well -- nuts!http://www.pelicanparts.com/support/smileys/shake.gif

The 2.2 rod is an update to the early rod and was designed to be stronger and it is. For all of you who prefer 2.0 rods to 2.2 rods we have 30 sets and we would be happy to trade any good set of 2.2 rods for 2.0. We also have 2.0 "S" rods to trade or sell.
Sometimes you give up weight for strength.

Henry,
What is different about the "S" rods?

"S" rods are nitrated.

What does the nitriding lend to the characterstics of the rod. I can understand cranks, but rods?

Nitrating helps to prevent surface cracks that lead to catastrophic rod failure. The effect is similar in purpose to the shot peen process used by many American V8 engine builders. Some people even believe that these processes add overall rigidity to the rod.

Interesting; so would you say nitrided rods 'S' rods are superior to conventional 2 liter rods for the purposes of building a high reving short stroke motor? Can conventional rods be shot peened to the same effect of nitrided 'S' rods?

Or,

would you still shot peen a nitrited rod, or does that not work/no benifit.

Ed

I'm not certain.
I would guess that shot peening is less affective.
The shot peen process only puts a very thin layer of surface material in compression to help redistribute stress.
Nitrating hardens the surface as much as .020 deep creating far more stress resistant surface.

* Please remember that I am not an engineer just a lowly mechanic and that the opinions stated here are only from my somewhat limited experience. *

Hmmm; I am considereing non-nitrided 2 liter rods for a motor build and want opinions on whether they would be sufficient for a motor that would spin to 7800 RPM.

Henry, have you or would you build a motor like this on these rods?

The controlling factor for Supertec is piston weight.
A high performance SS 2.8 piston (95mm) generally weighs at least 100 grams more than say a 2.0 piston (80-81mm). With the heavier pistons we run the 2.2 rod. It (the 2.2 rod) is heavier but far stronger.
We have both in stock for sale.

Talked to my metalurgist. He is also a drag racer, so he understands these concepts. He has never heard of nitriting rods and feels that the advantages of the nitriting (which is usually used to help with wear resistance) would be less than shot peening. Shot peening, he feels, would do a better job of stopping crack propagation

He also went on that the shot peening a nitrited part may diminish any advantages the nitriting had becasue it would disturb the very thin layer of nitriting.

Overall, he would rather have a shot peened rod than a nitrited. He is not sure of where the nitrited then shot peened would fall.

Thanks

Ed

Opinions do vary. That's what makes a car race.
Porsche Nitrited the rods, we know that. I wonder why your guy doesn't know that?
Some people race in a straight line for 5 seconds, others race in all directions for 24 hours. To each his own.

We are not a Porsche shop. We make various products (mostly high precision turnings in high production) for the auto industry.

His expertise is in metallurgy. All things metal and the heat treat of them. He is in charge of our heat treat department and development of new products. It is not in Porsche specifically. His only knowledge of Porsche is what I tell him.

Nitriting rods on a production basis is much faster and much cheaper than shot peening. Shot peening lines can be set up for production (I quoted on installing one for torsion bars for power steering applications) but it is much more specific. I was looking at volumes more like 5 million parts, not 50,000 parts. Would not be cost effective vs doing by hand.

Thanks

Ed

The early Porsche spec book does indeed say that the 911S rods are "seft nitrided." However, the 1969 book simply says "forged steel, (stress-relieved).

These books contain lots of typos and errors (which I found out while I was writing the Engine Rebuild Book), so I wouldn't necessarily believe 100% of the stuff written in there...

-Wayne

Nitriting is a process that can be identified visually. The books have a great deal of good information but sometimes experience can answer questions the books can't.

Please remember that Porsche was a very small company that did not always have perfect internal communications.
I think this is something the concourse fanatics seem to forget. Written in a spec book or on a brochure was not always how a car or part was delivered.

What about SS 2.6 piston (92mm RSR)? Is it safe to use 2.0 rods for this?

We would use 2.2 rods for that aplication.

2.8rsr piston
 

would an earlier rod such as the 2.2 be prefered over the 2.4/2.7 rod for the 92mm rsr pistons?

Re: 2.8rsr piston
 

2.4 -2.7 rod has a different bearing size and will not fit a 2.0-2.2 crank.
The rod lenth is also shorter on the 2.4-2.7 rod.