Rocker Arm Selection - Pontiac GTO Forum
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post #1 of 5 (permalink) Old 01-01-2015, 09:03 PM Thread Starter
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Rocker Arm Selection

Hi.. I'm rebuilding a set of 62 heads for my 400. I got a "high performance street" 1800 to 6000 rpm range Comp cam kit that includes valve springs. I suspect this engine will only occasionally see 5000+ rpm. One of the many things I need to buy are rocker arms. I see there are lots of options at Summit. Any better or worse than others or make any difference? Some better for some applications than others? Any real difference in performance in one vs. the other?
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post #2 of 5 (permalink) Old 01-01-2015, 09:24 PM
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The opportunities for performance gains from rocker arms comes in the form of reduced mass and reduced friction. Obtaining those benefits usually means aluminum rockers with needle bearing fulcrums/trunions and roller tips. Go with a quality brand. This is an area not to try to cheap out on, since the consequences of having a rocker arm break while the engine is under load at rpm are very ugly. I run Scorpions in my 461. Harland-Sharp is also a long time supplier of good rockers for Pontiacs. If you're contemplating going with rockers that have more than the factory 1.5:1 ratio, make sure you elongate the pushrod passages in the heads for additional clearance, otherwise the pushrods will rub on the heads and "bad things" are likely to happen.

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post #3 of 5 (permalink) Old 01-01-2015, 11:45 PM Thread Starter
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Thanks Bear... I'm planning on going with the 1.5s. How much of gain can I reasonably expect over stock rockers? Did the scorpions do much for you?
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post #4 of 5 (permalink) Old 01-02-2015, 07:00 PM
 
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Is your comp cam a "thumper cam"

EdR - is the comp cam you picked one of the "Thumper Cam" series?
Also, what size cfm carburetor will you be using?
I have a factory 389 that I am working with and wanted to check on these items with your project - thanks.
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post #5 of 5 (permalink) Old 01-03-2015, 09:58 AM
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I built my engine "all at once" so it wasn't possible to discern what effect the rockers by themselves had. However, when you stop to think that fully compressing just ONE valve spring can require 300+ pounds of force it's not hard to understand why operating the valve train is one of the largest causes of parasitic power loss in an engine. Still, there are compromises. Contrary to popular belief the Pontiac factory engineers weren't idiots. Those stamped steel rocker ball setups they designed (which, by the way are THE reason the small block chevy ever came to exist) are very strong, durable, and reliable. When you replace them with "something else" you've got to pay more attention to them in keeping on the lookout for wear and damage that can lead to failure and a destroyed engine. It just comes with the territory.

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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO General Discussion

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