2.0 vs 2.2 rods
 

As you may know, BA prefers the 2.0 rod over the 2.2
However I can't see why because the latter look very much like the 2.4 rod and beyond. What's wrong with 2.2 rods?

Do a search, mucho info is out there.

blue72s; I believe that some people have a preference for the 2.0 rods because they are strong enough, and significantly lighter then the 2.2's. I believe that a comparison of the weights was posted here previously. Did you find what you wanted by doing a search of this BBS? I did a quick search and found a couple of pages of threads just in the "911 Engine Rebuilding Forum" alone.

I did a search and found some info but nothing about rod weight comparisons.. Could you pls post a link?

Here's a comparitive picture of (L to R) a 2.0 rod, a 2.2 and a 2.7 rod.

http://forums.pelicanparts.com/uploa...1105483971.jpg

I weighed the 2.0 and the 2.2 rods (both with bolts but no nuts since I was missing nuts for that particular 2.0 rod and I wasn't in the mood to rummage around in the cold garage for another one :rolleyes: )

2.0 Rod: 608 grams
2.2 Rod: 702 grams

The biggest difference between a 2.0 and a 2.2 rod (to my eye) is in the robustness of the rod cap. Note the length of area through which the bolt runs on the two rods. The 2.0 also has noticably less material across the cap.

PS: Yes, the 2.7 rod is junk (note the extensive discoloration). It had a spun bearing in it when I tore down my donor motor. The rest of them have already been sold and I kept this as a conversation piece.

jluetjen,
Is that my old 2.2L rod :)
We got the 2.5L running. Boy that thing is nice! I was spinning the tires in second gear (Kumho's) I could never do that with my stock 2.7 so easily.

Yup! SmileWavy

Soo, which is better? Yes, 2.0 rod is lighter but is it at least as strong?

did you weigh with or without rod bolts?

i weighed my 2.4's , 2 weeks ago , and they were all around 600 gram

I weighed it with the bolts, but without the nuts since that was the way that they were at the moment. I didn't have time to do more then that.

"Better" depends. :rolleyes: I doubt that the 2.0 rod is "at least as strong" as the 2.2 or else why would Porsche have redesigned it? The critical factor question: Is the 2.0 rod strong enough? If the answer is yes for the application in mind, what's the benefit of the extra weight of the 2.2 rod?

Both John and I have different ideas on this subject. Which is great because we traded rods with each other (I gave him my 2.2L rods and he gave me the 2.0L rods)
John has some valid points.
My way of thinking is this. We have never seen a 2.0L rod "break" in our racing motors. What does causes a rod to "break" is a prior malfunction inside the motor. Example- oil not getting to the bearings, or oil starvation under braking, excessive bearing wear/heat etc. If any of those things are happening, ANY rod will break regardless who made them (Pauter, Carillo, or a stock Porsche rod, etc). We have seen our share of broken Carillo rods and gave up on those. Way too much $$$$.
So we stick with the 2.0L rods for the lower weight (remember there are six of them :p ) This helps the motor spin faster with less weight moving around inside the motor. Again, a 2.0L rod will not just "Break" there are compounding problems that will cause ANY rod to break.
Either rod will work in your motor great, so you cant go wrong.

BTW John, Nice choice of granite.... we have the same granite in our house :)

With or without bolts? and nuts?

Your engines or race team factory engines?

In "our" race motors. Most guys we race with have 2.0L rods and rev the #$@% out of them. None that I am aware of have had a rod just snap by its self. If we saw 2.0L rods breaking, we would not have them, and friends would not have them in the race motors Now if you have something like 16:1 compression and 400 HP thats a different story :)

Actually Chad; I've hedged my bets since I have at least an engine's worth of 2.0 rods still here. I figure that I'll use the 2.2 rods for version 1.0 of my engine since that will get a bunch of practice time, driver's schools and regionals use. After 2 or 3 seasons when I redo the bottom end (engine spec 2.0) , I'll check out how the 2.2's held up and potentially switch to the 2.0 liter rods for a no-holds-barred national motor.

One good reason to go with the 2.0 rods is that you can buy ARP bolts for them. You cannot get anything but stock for the 2.2. That being said I am using 2.2 rods in my race motor because I believe they are good enough for me.

Henry Schmidt pointed out in this thread that the 928 bolts will work as a replacement for the 2.2 bolts. A set of Raceware bolts for the 928 is $400 and you'll have an extra 4 left over as spares.

I reread that post and Henry said he used 928 rod Nuts, not bolts. You might want to revisit that post.

yes you're right:

What about the 2.0 factory bolts? Are they also up to the task?

I would suggest using ARP rod bolts for the 2.0L rods. You can reuse them and not have to worry.

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.