I posted on a separate thread that I am in the process of building a proper 1962 340hp short block. I have a NOS GM Duntov 97 cam but I do not have a cam card. Does anyone have a pic of a cam card for the Duntov 97 that they could share? Thanks
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Re: Cam card for Duntov 97
Not a cam card per se but I did dredge this up from my tech library... -
Re: Cam card for Duntov 97
Helpful. Thank you. I think I need a little more information as I want my machine shop to degree the cam. Typically a cam card has all the info needed by the engine builder to setup everything correctly. ThanksComment
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Re: Cam card for Duntov 97
Yes - I have the cam card for the rebuild done by previous owner of my 61 270hp car but I'm sure it was tweaked from the factory Duntov specs so I won't bother posting it...Comment
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Re: Cam card for Duntov 97
Please explain what you mean by "degree the cam."
DukeComment
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Re: Cam card for Duntov 97
Per the GM print the Inlet Point of Maximum Lift (IPOML) is 108.5 deg. ATDC. If the cam came from a reputable manufacturer and you can say the same about the timing chain it should be within a degree of this, and I don't think it's necessary to check. Hotrod lingo refers to the POMLs as "centerline", but since most modern cams have asymmetric lobes the POMLs are not the same as the actual center of the lobe. Of note is that the Duntov cam lobe is symmetrical, and it's my understanding that he actually designed the lobe back in the forties for his Ardun engine. Even the 1957 base engine cam that was production through '66 has asymmetrical lobes.
The EPOML is 112.5 deg. BTDC, and since the LSA is simply the arithmetic average of the IPOML and EPOML, it's 110.5 deg.
This is the way the cam is ground. So in hotrod lingo (that I utterly HATE) this cam has two degrees of advance "ground in". If it was ground "straight up" the IPOML, EPOML, and LSA would all be the same, 110.5 deg.
Isn't it much easier to use the as designed IPOML... and advance or retard from that rather than this "ground in advance" and "straight up" nonsense?
Ten years ago when I was looking for someone to grind two cams I designed I went to a small Southern California cam shop that most of you old timers have probably heard of. I was looking for a couple of lobes and were in the ballpark of what I wanted. He had a couple of candidates, but when I asked him if he could grind a specific IPOML and LSA, he said he couldn't tell me what the IPOML would be. I would have to "degree it in". Needless to say I thanked him for his time and left.
I ultimately had Crane grind the cams using four different OE lobes and they all measured to my specs, including the IPOML and LSA that I specified.
The Duntov cam lobes are the same on both sides other than the exhaust side having a .004" higher clearance ramp. It doesn't take into account the relatively restrictive exhaust port on later "big port" heads by using more duration and has harsher lobe dynamics. Chevrolet learned a lot about lobe dynamics beginning in the early sixties with the Optron and the ultimate SB mechanical lifter cam was the LT-1 cam designed circa 1969, but it wasn't really "all new". The inlet lobe is the L-72 lobe on a slightly smaller base circle, and the exhaust lobe is the 30-30 lobe. Both of those cams use the same lobe on both sides. Having the somewhat longer 30-30 lobe on the exhaust side, phased fairly early, mitigates the restrictive exhaust ports.
I recommend the LT-1 cam to replace the Duntov and 30-30 on 327s and 350s. Given that it has about the same effective overlap as the Duntov it has essentially identical idle behavior, but will make more top end power. The LT-1 cam has less effective overlap than the 30-30 (for more low end torque with about the same top end power), but several who have used the LT-1 in place of the 30-30 say the idle behavior is essentially the same.
DukeComment
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Re: Cam card for Duntov 97
I have degreed a cam only one time, but I found it not too difficult, and I felt better for at least having spot checked the indexing. Maybe because I was not too practiced, I did find it somewhat easier to verify the .050 lift points, as compared to POML.
If your Duntov cam is a real NOS part, maybe you don’t have to do that at all, I don’t know.
Anyway, for the .050 lift points, here is what I calculated from the cam lift table, to the nearest half degree:
Int open 4.5 BTC
Int close 41.5 ABC
Exh open 47 BBC
Exh close 2 ATC
Duke can check my numbers if he would like!Comment
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