Thread: Techinspector1's cam recommend was right on! More questions on cams

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"has a shallow valve closing ramp to smooth out the drivetrain, and make it last longer."

pnut, I'm not sure what you are thinking here, but I'll give you my take on short ramps.

As I've explained before, a fellow can determine the length of the clearance ramps on a lobe by subtracting the 0.050" tappet lift duration figure from the advertised duration figure. Well, you can't figure the whole ramp this way, but you can get close enough for comparison purposes and that is what we're interested in here. In other words, if a cam has 0.050" lift duration of 230 degrees and an advertised duration of 280 degrees, the difference is 50 degrees, or 25 degrees on the opening side of the lobe and 25 degrees on the closing side of the lobe. Now, some lobes are ground with these clearance ramps being symmetrical and some are ground non-symmetrical. Again, for comparison purposes here, we'll assume a symmetrical lobe.

Now, if you picture the lobe coming around to make the lifter begin climbing in its bore, it is understandable that if you have less clearance ramp, the lifter will rise more quickly and there will also be quite a lot more pressure on the lobe/lifter interface than if you pushed the lifter up more gradually with a longer ramp.

Back when I was a kid, it was common to see a cam ground with 70 to 80 degrees difference (35 to 40 degrees on each ramp). But competition does strange things to a product. In order to bring something new and exciting to the market, some manufacturers began to snap the valve open and closed for more "area under curve". Comp uses the term "extreme energy" to label their products that use this design. While it is true that you can have the valve open longer for the same duration design with a "snappy action" cam, it also puts a tremendous amount of stress on the lifter/lobe interface and tends to "wipe" the lobe of lubricant more easily, leading to failure.

Another contributing factor to this cam failure epidemic that I've been seeing lately is the lack of extreme pressure lubricants in motor oils. I can't remember the others, but I know zinc is one of the minerals being left out of oils lately due to the negative impact it has on calalytic converters and the increased pressure from car makers to produce a car that will live to 100,000 miles. I very strongly recommend that any of you high performance enthusiasts out there who want additional protection use some of the specially formulated racing oils that still have these additives in them and also to always keep a bottle of GM Engine Oil Supplement in the oil. It is formulated with molybdenum disulphide, a very good extreme pressure lubricant which will help protect the cam lobes/lifter faces.

Originally Posted by techinspector1

"has a shallow valve closing ramp to smooth out the drivetrain, and make it last longer."

pnut, I'm not sure what you are thinking here, ....... Now, some lobes are ground with these clearance ramps being symmetrical and some are ground non-symmetrical. Again, for comparison purposes here, we'll assume a symmetrical lobe.

You hit on a point here. The lobes on the voodoo series actually IS assymetrical. The opening is quite quick to give "more area under the curve" to quote Lunati's description. But it goes on to say that they close more slowly to reduce the extra stress which would be caused by fast closing.

So now I have to decide if the fast opening and the associated risks are worthwhile. I think my answer will be yes. From the research I have done online, the voodoo cams have been spoken of favorably.

I did ask the Lunati tech if the springs which came with my Holley heads (assembled) were appropriate for this cam, and he said yes. The are single springs, I have to look at the spring rate and compare those to the springs recommended on my own to be sure.

I did decide to go one cam tamer however. I will be installing the 60101 instead (looking at Lunati's site on the cam details and description). The 60101 gives and even lower rpm torque curve.

Thanks for all the advice, and I will degree the cam (an extra 2 degrees).

[QUOTE=techinspector1always keep a bottle of GM Engine Oil Supplement in the oil. It is formulated with molybdenum disulphide, a very good extreme pressure lubricant which will help protect the cam lobes/lifter faces.[/QUOTE]

Is this a GM part only? Maybe there is a parts store substitute that could be used? I am interested in more specifics so I know exactly what to buy (either from the dealer or at parts store).

Thanks techinspector1