Havent tested mine but my tds look steel. See if a magnet sticks to them when i get home.

As for the op, id go comp cams over the scorp ones

 

They should be 2024 Aluminum.

 

Aluminum will degrade faster than steel. Period. Its metallurgy and there's no getting around it. It has half the fatigue performance as steel and aluminum doesn't have a fatigue limit, like steel does. A 'fatigue limit' - its the point at which you can apply a certain measure of stress, flex the metal, and it will never break as long as the stress applied stays below "X". Once you exceed that limit, you weaken the steel and lower its fatigue limit. As long as you keep the stress below the "new" fatigue limit, you're good to go.

Aluminum, by contrast, doesn't have a fatigue limit. It has a distinct point where once you exceed its ability to handle stresses, it will break. In other words, think of aluminum rockers as having a built-in number of cycles they can handle. Once you exceed that number, they break. Steel doesn't have any built-in limit. Keep it below the rated stress-capacity and it will cycle forever.

Does this mean that ALL aluminum rockers will break someday? Actually, yes. If you have an engine that will theoretically run until our sun burns out, keeping the exact same spring-pressure against the rocker - eventually it would find the point of failure in every single aluminum rocker. Steel, if kept below its fatigue limit, will go on until the end of time. Edit: This is one reason why airframes have a set number of hours they can be in the air. Once those hours have been exceeded, the airframes are retired and no longer flightworthy because they could fail catastrophically at any point - without any indications of stress.

That being said, GOOD aluminum rockers, such as the TD's, or other high-end aluminum rockers - will probably outlast your engine's ability to pollute the atmosphere. However, they will break before steel. They will fail before steel.

 

I went with the Comp Pro Mags on my truck with its wimpy 196/206 .431/.451 Ramjet cam because I wanted as many issues as the factory stuff gave me: none. That said, I'd probably go Crane gold/GMPP if I did it again so I wouldn't have to trim the little bridges on my valve covers. Now if I were running something with a healthy cam, I'd just stick with the Pro Mags. They're dead silent like stock unlike the Ford Cobra RRs I had in a 5.0 years ago.

 

Are there any tests with aluminum/steel rockers to prove the aluminum will fail first? Reason I'm asking is because the body of an aluminum rockers has a different design and uses more material than steel. I can see this being true if forces are being applied to the same amount of materiel and same design, but because that doesn't hold true, at least in the roller rocker world, it would be interesting to see the comparisons.

 

Not exactly what you are asking for, but a good mile-high view

http://www.superchevy.com/how-to/eng...er-arm-design/

 

Aluminum rockers are larger than steel ones simply because it requires more mass to be comparable in strength to a steel body rocker.

Using race application parts as a basis for longevity is not always viable. Most parts are designed for highest power lowest weight with reliability made a lower priority. Parts designed for this are assumed to be periodically inspected and replaced, not just "set it and forget it".

 

Which is why I was asking if there is a difference since there is more material and a different design.
Good read, but because it is based more on durability for NASCAR there really is no comparison to the average LT1 build, which means there shouldn't be an issue between a quality aluminum or steel rocker.

 

It has everything to do with an average LT1 build. Lessons learned through racing durability easily translate into a street car. 2 hours at 11,000 RPM's with sky-high spring pressures is a perfect laboratory for learning all sorts of things about rocker design. Its not a 1:1 ratio, but to look at things learned on the track and say "this has nothing to do with a street car" is a bit odd.

For the past 100 years, most of the progress seen in just about every part of a performance street-car is deeply rooted in racing.

 

I must not have been clear in what I meant in my last post. Of course the R&D is important. What I mean is, the average build should not have any issue regarding the longevity between a quality aluminum or steel rocker as they both will do well.

 

Ok, so apparently all of these rocker manufacturers have it 100% wrong, and every rocker should be made out of uber steel. Jesel= junk, TD= junk. Stamped steel stockers FTW!

 

Yup that was exactly what was said.

 

I'll just leave this here:

 

[QUOTE=atlantadan;19559765]

Aluminum, by contrast, doesn't have a fatigue limit. It has a distinct point where once you exceed its ability to handle stresses, it will break.

Trying to clarify, so does the "Stress Limit" not in direct correlation to the Fatigue limit?

Steel, if kept below its fatigue limit, will go on until the end of time.

So if aluminum is kept below its "Stress limit" will it go to then end of time?


Edit: This is one reason why airframes have a set number of hours they can be in the air. Once those hours have been exceeded, the airframes are retired and no longer flightworthy because they could fail catastrophically at any point - without any indications of stress.

Quote from Boeing: Boeing has found of late, that is easier said than done. The biggest problem aircraft engineers face is that the fatigue cycles a component faces are cumulative.

I know like aluminum rods, at a point of several high RPM runs the rod will actually stretch a bit and steel will not.

 

Not when talking about aluminum. Aluminum does not have a fatigue limit. This means that aluminum will fail eventually even at small stress levels. It may take a thousand years of constant exposure to that level, but it will break. Every aluminum part has a pre-loaded number of times it will take any stress. Exceed that magic number and it will fail. I suspect this is what the Boeng quote is about. Each fatigue cycle counts towards that number.

 

Everything you posted has nothing to do with the longevity of a quality aluminum rocker then, correct?

 

Um, no, that's pretty much the opposite of what I said. Everything I've posted has to do with aluminum in-general, of which some rocker arms are made of. The intent was to point out that while high-end aluminum rockers are probably a-ok - they are not as durable, or as forgiving as steel. Steel is just an all around stronger material - but at the added cost of weight.

The TD shaft rockers that Joelster runs are probably $1200+ and a killer bit of kit that would probably knock valves down for a thousand years, but the OP wasn't looking at Jesel or TD shaft rockers. They were asking about sub $350 rockers. In that class, the $30 between Comp Ultra golds and Comp Ultra ProMags is a no-brainer because its cheap insurance. On a street car, the extra grams on the valvetrain are a non-issue, and at this price point, the risk of aluminum failing is much, much higher than a TD or Jesel. (Unless you're going to argue that the high-end offerings from TD are comparable to Comp Golds in engineering, materials purity, and construction - at which point, I'll defer to other minds on this forum.)

In the end, its down to empirical evidence: Having had a Crane aluminum rocker break at the shaft on a mildly cammed 396 big-block in my 66 Chevelle SS, I just don't trust them. YMMV.

 

Steel is stronger than aluminum but heavier and vice versa.

 

Not arguing. I'm just trying to understand your point. You did not define what you meant by "good quality" until your last post. Because I ran the Crane rockers for seven years on the street and some track use without issue, that's what I define as "good quality." And now that you've stated you had a bad experience with one, I can now understand your bias.

Edit- One thing I forgot to ask, are the good quality shaft mount aluminum rockers that much more durable than a stud mount because of design, or is it because a shaft mount offers more stability/less harmonic interference?

 

I have steel shaft mounted rockers on my SR 398ci......Comp Cams.

Not sure if Comp makes them anymore.....I bought them back in 2004 because the were steel. Otherwise, I'd have stuck with the Pro-Mags.

KW