Promagnum rockers are made from 8650 chromemoly
Hitech stainless rockers are made from 15-5 PH stainless steel

Sounds like the stainless rockers are much stronger than the promagnum rockers...how much stronger?

But it sounds like the promagnum rockers are much lighter (comp claims 5% lighter than aluminum rockers)...no claims on weight of the stainless rockers compared to the promags. Anyone have info on this?

The question is. In a relatively large lift valvetrain setup, not spinning crazy fast (sub 7000rpms).

Where would more power gains be seen? From strengthening the rocker to decrease deflection in the valvetrain and "regain" lost power there?

Or would it come from a lighter weight 'train, assuming the promags are at least a little lighterweight?

Also just to have some examples to put these rockers on. I am curious because I will be running a hydro-roller 570ish lift spinning up to 6500, but might think of using a similar sized(not crazy radical) solid roller later on this year, and dont know if either one of these rockers would be up to the task, or if shaft mounts are in my future?

 

I've abused my ProMagnums and never had one fail yet. I actually have a spare set but have never needed to use them yet. Some day I'll send them in to be rebuilt.

I also have a set of Crane Energizer aluminum rockers but would never use them on my race engine. The roller cam that I'm going to be putting in would probably break them. They'll go into my next street engine.

I broke a Crane Gold with 7/16" rocker stud in a SBC. The trunion itself broke not the rocker. It was replaced under warrenty.

Shaft mounts are nice but at 3-4x the price you really need to be able to afford them.

 

Those stainless rockers are nice, but I can't say I know of any street/strip motor using them. IOW, they are way overkill. I think they would be something to consider for a motor using very stiff springs that runs at high rpm for long periods.

Rich Krause

 

My Comp stainless rockers see 8000 RPM on just about every pass. 100 runs and counting. No problems as yet.

 

One thing about Lingenfelter engines, a bit pricey, but they WERE dependable/durable.

 

The weight won't mean much unless the two rockers are identical in design. The term you're after here is moment of inertia and it's dependent on the distribution of mass throughout the rocker arm. You can have two rockers of exactly the same weight, yet different moments of inertia.

As for strength, you can look up the materials (tensile strength, young's modulus, etc..) but that's not going to tell you a whole lot. If it were as simple as comparing two different material types, there would never have been a need for finite element alalysis..... and I would have been a jobless dude some years ago.

-Mindgame

 

Alright, well since no one feels like comparing strengths and moments of inertia of these two (no biggie, dont blame ya), how bout an opinion...which would you pick in my situation?

 

The ProMagnum 8650 chromemoly steel is stainless. They're completely rebuildable by Comp Cams and Comp guarentees the body will never break for life.

 

Has to be greater than 10.5% Cr content to be classified as "stainless". 8650 chrome moly is... well, chrome moly.

Save your money... the Pro Mags will be just fine for what you're doing.

-Mindgame

 

It resists corrosion, but its not Stainless Steel right.
Im not worried about breaking them at all, Im looking for the least amount of deflection vs valvetrain "weight" ratio as possible, for $50 extra bucks or whatever to go to stainless to gain a few hp I wouldnt mind doing it. But if its a total waste of $ in my situation then i wont.

Edit: mindgame, thats whta I wanted to hear, promags it is...unless I feel like spending another $500 for some jesels or t&d, im sure I could gain some power there but the $:HP ratio just isnt good in that case.

 

How much corrosion are you going to see under the valve covers. The rockers are constantly soaked in oil.

Now under my valve covers there's a chance of corrosion. Running alcohol my engine runs cold and my oil is always contaminated with alcohol and moisture. When I pull my valve covers it looks like mayonaise under them. I change my oil after 3-4 race weekends depending on how many passes I make.

You won't need shaft rockers until you get well over 600 pounds spring pressure when the valve is open. For a typical street/strip car, 300 pounds open is a lot.

 

Well after reading the thread on shaft rockers a little while ago there is power to be gained in that area on almost any car, not to mention valvetrain stability right?

Im at about 450 open now on a hydro, but I guess doubt even breaking 600 with a solid in the future.

 

The Hi-Tech Stainless rockers are made from 15-5 PH or precipitation hardening stainless. Both these and the 8650 Pro Mags are investment cast and heat treated after machining.

If they are at similar hardnesses, say Rc 38 or so, they are 130,000 psi yield, 160,000 tensile strength parts. I believe the 15-5 can make a stronger part than 8650 when both are cast.

Rocker arm stiffness or how much it deflects when loaded by the pushrod and valve spring are a big factor in how your valvetrain operates. Everything is a spring, but these rockers are very stiff springs. maybe 52,000 lb/inch springs, according to Comp.

If you have a good engine simulator, vary the stiffness of the rocker arms on a 6500+ aggressive roller engine and notice what it does to hp curves. I'm not sure if all simulators have this option.

 

If I remember right, when Comp says the pro mags are 5% lighter they are saying they have 5% less weight on the valve tip. It could weigh 10 times what an aluninum rocker did and still be balanced in such a way.

The Promags are a VERY strong rocker, just not the lightest one . Im pretty sure the stainless comp rockers are lighter and stronger, but Ive never heard of anyone breaking a ProMag. Its more a question of how much do you want to spend and do you want it strong or strong and light. It just keeps co$ting more heh!

Doug ( the Pro Mags were good enough for me) J


"But it sounds like the promagnum rockers are much lighter (comp claims 5% lighter than aluminum rockers)...no claims on weight of the stainless rockers compared to the promags. Anyone have info on this?"

 

I'm a big fan of Hi Techs for Solid Roller cars if you are not doing shaft mount rockers. The added spring pressure in a solid roller will cause deflection issues, so the least amount of deflection is the best thing to do.

Were not really worried about breakage here, that's not the point, nor is it corrosion. As Old SStroker said it's the material strength that counts here.

On a Hyd Roller motor a Pro Mag can do the job, it's still going to deflect more than a Hi Tech will, but there is a $$$/hp tradeoff that doesn't make much sense at that point. The added stiffness will help.

The rocker arm weight is not as big of a deal compared to the stiffness. True a heavier rocker is like having steel retainers vs. Ti ones, but deflection is more important in things like rockers, studs and pushrods rather than weight is. If you can get both lighter and stiffer parts then you are going to do even better.

Bret