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Re: 151 valve timing question
That cam is not Parkerized, but it's not necessary on a roller cam. If Parkerized the lobe would have a mottled gray finish and look very different from the jounal surfaces, which would be silver as in the photos because the Parkerizing is polished off. It might scratch cam bearings but it's slighly porous and holds oil, which aids break-in of sliding surfaces.
Advancing/retarding the cam will slightly shift the torque curve down/up the speed range, but IMO if you have to advance a cam to get sufficient torque, the cam may be too big.
Retarding the OE cam is often a good option on strokers. In the case of the ...962 cam it was already retarded by Chevrolet by grinding it to a 114 deg. ATC POML. This was very late indexing for the era. Modern Corvettes are in the 116-120 range, but have shorter duration. Modern valve timing philosophy is very different from fifties to seventies thinking. The ...151 is 110, and that's why I recommend advancing the 962 back to 110 if used in a 327.
Flat tappets have a very slight convexity to the surface which causes the lifters to rotate in service. New cam an lifters should always have MoS2 assembly lube smeared on the contact surfaces.
DukeComment
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Re: 151 valve timing question
Oh, so your saying, the lobes have a slight parkerizing on their lifter contact surfaces and this traps oil to help lifter break in. Whereas a polished metal surface that won't trap oil. Have not considered this. Does the advanced 962 idle the same as the 151 camshaft?Comment
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Re: 151 valve timing question
The ...151 and ...962 cams both have about the same effective overlap with the ...962 being marginally higher due to two degrees more .050" lifter rise duration, but this does not have a noticeable effect on idle behavior. The design indexing of the ...151 is 110 deg. ATC inlet POML and the ...962 is 114, but I recommend advancing the ...962 four degree with an adjustable timing set to 110 on 327s, which have less stroke than 350s.
The most significant factor in idle behavior is effective overlap, which is measured in square-inch-degrees and takes into account valve size,but as with the slighly different duration, the difference between the 1.94/1.5" set and 2.02/1.6" set will not have a noticeable effect. Likewise indexing has little effect and for either cam the difference between indexing them at 110 deg. ATC and 114 will have no noticeable effect on idle behavior.
Bottom line: both the ...151 and ...962 have the same idle behavior with any reasonable indexing and either valve size.
As I said, Parkerizing aids the break-in process for flat tappet cams. All OE cams were Parkerized as are current replacement GM cams. The only other cams I know of that are Parkerized are Federal Mogul (Sealed Power and Speed Pro brands) Dana Corp. (Clevite brand) and Crane.
An old OE cam that is removed will usually not show evidence of Parkerizing, because it wears off the lobes in service.
DukeComment
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Re: 151 valve timing question
No, I am not even a little confused.
Camshafts are designed with a specfic indexing relative to the crankshaft, which is usually expressed as the inlet POML being at some degrees ATC, The as designed indexing of the ...151 cam is inlet POML at 110 deg. ATC and the ...962 is 114, which is four degress retarded relative to the ...151.
If one installs either cam with an OE equivalent non-adjustable timing set then the indexing will be as designed assuming the camshaft was properly manufactued to the respective GM print.
If one wants to vary the indexing from as designed, then an adjustable timing set is required, and I recommend installing the ...962 in a L-79 with an adjustable timing set to bring the inlet POML back to the same point as the as designed ..151, which means ...962 is installed four degrees advanced from the design indexing. If the ...962 is installed as designed there will be a loss of low end torque, and even though top end horsepower should increase, it may be beyond valve train limiting speed, especially with massaged heads.
Hotrodders and most cam grinders talk about a a cam being "advanced" or "retarded" or "staight up", but relative to WHAT?
It's more precise and understandable to say a cam is advanced or retarded from it's design/as-manufactured indexing, which is usually stated in the basic camshaft specs.
But, some cam manufacturers can't even get it straight. I talked to one about a custom design, and he could not tell me the inlet POML indexing as it came of his grinding machine. He said I'd have to "degree it in".
Needless to say, I went elsewhere because my design had a specific design indexing spec, and that's the way I wanted it ground, so it wouldn't require an adjustable timing set and diddling around to find out the as-manufactured indexing and then having to correct it to the as designed indexing. I left his shop shaking my head in amazement.
Hotrodders and the aftermarket also refer to "centerline" - what I refer to as point of maximum lift or POML. On many cam designs the POML and "centerline" are not the same due to lobe asymmetry - the closing event is stretched out to soften valve seating. Symmetrical designs can cause the valve to bounce off the seat at high revs, and this is typically the first type of false motion that is seen on a symmetrical lobe design.
All OE Chevrolet production cams dating back to 1957 are asymmetrical except the Duntov, which is one reason why the Duntov design is obsolete. The other is excessively high jerk that appears beginning at the tops of the clearance ramps, and this is why the Duntov produces typically generates more valve clatter than other OE cams, which may sound neat, but it's hard on the valve train.
DukeLast edited by Duke W.; February 6, 2015, 02:37 PM.Comment
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Re: 151 valve timing question
Duke I pulled the cam out of the engine yesterday and it is parkerized. This is the comp cam.Comment
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Re: 151 valve timing question
Yes, that does appear to be Parkerized. While you're at it you should verify that you have proper valve springs. A lot of "engine builders" install gorilla springs even with OE equivalent cams.
Case in point: A local chapter member sent his heads to a shop with a "good reputation" for a refresh. The parts list was mostly an unknown brand to me - probably an outfit that only sells to the professional trade. With some Web research it appeared they make some parts themselves and just repackage some parts from Federal Mogul and Dana Corp.
I was able to cross reference the valve springs, and they turned out to be the springs designed for the first design Trans Am racing cam, which have considerably more force than the OE springs and certainly won't do the cam any good.
The '67-up production springs are Sealed Power VS677 and with careful setup they will rev to 6500+ before pump-up occurs. The were used on everything from 283-two barrels to LT-1s, and cost about 20 bucks a set if you shop around.
The local chapter member later had the engine completely rebuilt, which included installing correct OE equivalent valve springs.
DukeComment
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