george 351

Can someone with any knowledge on this subject please tell me the advantages and disadvantages of using either and also about their intended use.Cheers

xdclevo

The alloy rockers are usually beefier, so they can be made strong. The stainless can be made with less material for the same strength so possibley lighter. It is all about weight verses strength, especially when using radical camshafts and very high rpm as this is when the weight factor affects the drivetrain.

TruBlu351

aluminium vs steel........larger vs smaller.........

Would be interesting to see the weight comparison considering aluminium being lighter.

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XE Falcon
393 Tremec TKO 9"

Ohio XB

I would have to say in this specific case that the stainless ones would not be any lighter due to the small sizes of the components.

Aluminium rockers are perfectly strong enough for the street. Some are made from 6061 aluminium and I would stay away from those. It is labelled an "aircraft" aluminium and that impresses a lot of people. It IS a good all around purpose aluminium but not incredibly strong.

A stronger aluminium is 2024. Harland Sharp makes their roller rockers from this material and that is a major reason they are stronger than the competition. I've been through their facility and have seen the broken rockers (the competition and theirs) in their testing area. They design theirs to be a step above everyone else in strength (Harland Sharp was the original roller rocker) and they attribute a major factor of that being the use of 2024 aluminium. These rockers hold up to severe use in drag racing all the time. However I would guess that stainless rockers would be better in the most powerful engines (7,000 HP)? I don't know.

For the street I would stick with aluminium roller rockers. If the stainless ones are conventional stamped style rockers and are cheaper I could see why someone would want to buy them. However you lose the friction reduction of the roller rockers.


Steve

davis

There really are three material choices in (full) roller rocker arms:




Aluminum:

Lightweight, easily produced (extrusion process), usually lower cost can have a dampening affect on high-lift, solid valvetrain components due to shock absorbing qualities of aluminum.

Lots of different manufacturers. Some brands are cheap knock-offs and may not even measure up to their specified ratios. Use a well-known brand name like Crane, Comp Cams and various others.

Excellent choice for good all-around performance on the street or at the track. Some believe that the aluminum becomes more brittle over time, so perhaps a steel rocker would be better for a street engine where higher mileage is anticipated.




Stainless:

Very strong/rigid. Due to the material strength, the trunions can be made larger in diameter and take more load than smaller diameter parts in aluminum bodied rocker arms. Usually much more expensive. Definitely not necessary for street engines.



Chrome-Moly:

Very strong/rigid. Due to the material strength, the trunions can be made larger in diameter and take more load than smaller diameter parts in aluminum bodied rocker arms. Usually somewhat more expensive. Definitely not necessary for street engines, but a good choice in race engines.


I run Comp Cams "Pro Magnum" chrome-moly rocker arms on my race and street engines. They are a good choice and only about $50 more than Crane Gold. However, they are also only 1.70:1 ratio, not 1.73:1 as are the Cranes. This takes a slight edge off of your camshaft profile, making it somewhat less aggressive.


:davis:

madmelon

The belief that aluminium becomes more brittle over time is incorrect. When they fail, it may look like a brittle failure, but every metal exhibits this property in a fatigue failure. It's all about crack growth. The good thing about most normal (carbon) steels and some stainless steels is that there is a level of stress that allows an infinite life with no fatigue. This is only important in tension (cracks don't grow by being pushed together do they...). SO provided they are operating under this stress level, steel and stainless rockers may actually last forever, but aluminium rockers will always die eventually. How longs depends on the stress level, but I imagine it would be a fair while- hundreds of thousands of km's.
Please note that something in bending stress like a rocker is actually under tension- on the bottom side of the rocker. Top will be in compression.

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1987 Jaguar Sovereign - Metallic Green
3.6L DOHC 24 Valve
140KW@4750rpm
307Nm@3750rpm (Flywheel)