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Re: Is this a can of worms?
I spent some time with a local Corvette friend (he can ring in and name himself if he wants) today, since the BIG, local, annual Corvette show was a rain out for many of us.
I was looking at some details on his all original/one owner '71 LT1. While checking out the ignition system, I took note of the VAC. Sure enough. It's not the 437 16 that's mentioned in the 4th edition '70-'72 JG. It's a 437 15, just like Fred's and Jack's original units. Note how in the attached photo, the oxidation line shows how all of the 437, and most (enough to identify) the 15 is visible with the dist cap on. I took it off to make it clear in the photo that it was indeed a 15.
This can of worms is wiggling. Terry, what gives you the confidence to maintain that the JG is right? Do we have hard examples of a 437 16 in an original car? The double asterisk note in the JG says "vacuum advance part numbers have been verified on original cars." This thread seems to be identifying the same for 437 15.
Why would there even be a 15 AND a 16? Would one unit require a different set up or would it perform differently than the other?
It's more than the 3 points to me. It's about learning and capturing what's learned in the JG.Don Lowe
NCRS #44382
Carolinas ChapterComment
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Re: Is this a can of worms?
One more for the pot !
another 437_15 photographed on the Delco Remy test specifications book DR-324 S-2. Go down the table until you find vac can 1973437. Note that the Max. Distr. Advance (4th column after part #) is not in CRANK degrees. So this is maybe where the 16 came from; [ie. 2 x 8].
This particular can is off a 1971 TI 1112038, which is the same can as for a 1112050.Comment
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Re: Is this a can of worms?
That is exactly where the 16* came from -- and why the ** paragraph begins with: "From Delco Remy Test Specifications. The purpose of that line is to tell you where the information came from. There is no hidden ball trick here, nor is there anything wiggling."
I do not recall adding the second sentence, and as best I recall the TIM&JG has been revised twice since the vacuum data was entered in 1999. Perhaps someone besides me added that sentence, or changed the sentence in editing, or another team leader (there have been several since my term) made a change. When I entered the vacuum canister data the only stamp that was verified from a survey of cars was the 1970 LT1. Any additional surveys were not on my watch, but that is not to say that there are none -- only that I didn't see them – and since I wasn’t NTL, there was no reason for me to see them.
I am a little surprised that there have been so many revisions with no one coming forward to date to suggest this list be revised. I would have taken it to the bank, given the lack of comment until this thread. That lack of comment here-to-fore is what gives me the confidence to say the TIM&JG must be right. If that sounds like blaming the messenger – so be it – and I’ll heap more blame. You guys who own 1971 and 1972 cars with this vacuum canister (and BTW I notice the absence of 1972 folks wading in with their information.) Have to be the ones to come forward with the information about your cars, just as owners of other years or options need to verify the information (and not just about distributors) in the TIM&JG, or provide missing information.
And I am obligated to point out that this thread carries NO weight on the judging field. If you want something revised in the TIM&JG you must present your case to the Team Leader involved. All this is just electronic masturbation unless someone picks up the ball and carries the data to the NTL. I would advise you to ask that TL what data he might find acceptable to make a change.TerryComment
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Re: Is this a can of worms?
JEEZ! Why don't we just let this run its course a bit? So far, (2) '71 and (1) '72 owners have shared that their original VAC is 437 15. I started this thread because I had a NTFP VAC and wanted to correct it. Couldn't find what's listed in the JG but could (and did) find a 437 15, which matches all that have posted thus far. We know there are other orig/untouched cars out there. Seems sensible that if more evidence of this comes in, it should be shared with the TL. I"ll do that, since I raised the issue in the first place, however, I tend to think that we should first hear from more owners.
BTW, I see this as technical discussion, not electronic masturbation. Questions bring answers. Answers (sometimes) bring conflict. Conflict brings discussion. Discussion brings resolution.Don Lowe
NCRS #44382
Carolinas ChapterComment
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Re: Is this a can of worms?
I am not suggesting to close the discussion, or the information gathering. I simply wanted to point out that unless someone picks up the ball and carries it to the TL, all this is a waste.
I suggested someone ask what his standards for a change are, so that you would know when you have enough data to meet, or exceed, his requirement. I doubt, but don't know, that three is enough -- especially given four different applications.
I would also suggest that this board may not have sufficient numbers of 1971 & 1972 participants to give sufficient numbers. You may have to go to judging events, or shows in order to gather more data points. Or contact 1971 and 1972 owners who you have previously communicated with. In my experience folks are more inclined to produce data if they are asked directly, rather than through requests such as this or an ad in the Driveline -- which might be a worth wile action anyway. The more avenues you explore, the more data points you will gather.TerryComment
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Re: Is this a can of worms?
Re Delco spec's --- the 437 can is not the only one where the max. crank advance is not precisely double the max distrib advance quoted in the Delco books. In fact, The books have an asterisk that refers to "plus or minus one degree". So maybe the manufacturer played it safe by fabricating (some) cans one degree below the spec to avoid exceeding it with his own tolerances. (just a thought)
Here are a few common C2, early C3 cans I have -- I've quoted the Delco max advance figure at the end of each line, so, by doubling it, you can see how close it comes to the stamped crank advance.
MS 201_15 (on can) ..... 8 (Delco)
--- 446_15 ................. 7.5 (bang on)
--- 437_15 ................. 8 (discussed yesterday)
MS 236_16 ................. 8.2
MS 238_24 ................. 12.5 (this 238 is another can (pun intended) of worms on 1965 1111076 distr's ?)
MS 163_16 ................. 8 (bang on -- a common replacement can)
MS 400_15 ................. 8 (rare can on Camaro 1111267 TI distr)
So you can see that on only two out of these seven, does the spec match the stampingComment
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Re: Is this a can of worms?
I wouldn't be 'jumping' on Terry, guys... We've chatted off-board and there are some 'curious' aspects to this issue (how was the '437 vac advance module was actually embosed?) spec'd. Plus, there's the issue of, regardless of specsmanship, how was the device physically embossed when it was manufactured???
I've always presumed that the text of the JG was a simple typo mistake. It literally never dawned on me that there might be a legitimate question here of right/wrong in terms of the actual emboss.
The reason I PRESUMED the text had a typo is because of how my car's (base '71) original vac advance is marked, plus what came in the 'Last of the Mohicans' service spare pull-string can that I pulled the string on (same: '437 15' emboss) as well as what I've seen at our shop on another three '71 Corvettes that 'appeared' to have untouched distributors on them...
Plus, my car has been judged a number of times and regardless of which revision of the JG book was used, the car's dist vac advance was never questioned. I attribute this off to judges lacking visibility and being in a hurry. So, the fact that my vac advance differs from the JG text and hadn't been 'called' simply seemed like a non-issue to me...
I now understand that Terry got the 16-degree figure from Delco spec documents. OK. But, let's take a look-see from another aspect and you'll see spec's can be tricky!
I've attached a snapshot from the 1971 Chassis Service Manual's distributor specication table. Note, the highlighted table entries are the two distributors used in '71 on SB engines and BOTH incorporated the '437 vac advance module.
Observe, their vac characteristics DIFFER! Both are claimed to obey the same C-3036 spec. But, the base engine car is claimed to exhibit 12-degrees of vac advance at 15.5"HG while the optional SB engine's vac advance exhibits 15-degrees of vac advance under the same 15.5"HG conditions. How does that happen given the vac advance module is the same phyical part????
So, I guess there IS an issue here relating to how parts are spec'd vs. how they were marked. But, Terry is right!
We've got a segment of JG text that apparently hasn't had a negative effect for MANY years. So, why change it based on 'knee jerk' analysis?
The key question is what does our current NTL, Stan, think constitutes proper and convincing evidence? We could pull the part drawing to see if the emboss is specified + did it change over time... We can do survey work to get a bigger sample size. BOTH avenues should work.
The question HAS been raised in the '70-72 NTL JG book committee and I think we'll get there, eventually. But, consensus needs to be proper and appropriate.Comment
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Re: Is this a can of worms?
Thanks Jack for the defense, but I have a thick skin from being around so long.
This thread does illustrate why many/most NTLs do not participate on this board. THey have a thinner skin than me.TerryComment
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Re: Is this a can of worms?
Jack your point about different distributors providing different specs using the same vacuum advance is easily explained by moving the vacuum advance rod closer to center of the pivoting plate (magnet) you can increase advance. Since both distributors are unique to the engines they were used on , GM wouldn't bare any increased cost. My '71 has the -15 advance and has 27394 original miles, CraigComment
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