More Info On "Batch Built" Rare Options ON C2 Corvettes(66)

[Larry E.]

I put a picture of my 66 (L72) Top Flight Corvette Differential on every now and then. As you can see
it has "Julian Dates" stamped on it.(No Year Indicated) Of all the pictures I have accumulated through the years I HAVE
NEVER SEEN A "FC" REAR END" with the normal "Year/Month/Date" on one. I have 3 to 4 pictures of
"FC" rears and all have Julian dates on them. I believe that all these rears(FC) where "Batch Built" at some point
at the "W" plant thus the Julian date on them. Please> Someone prove my wrong and show me a (FC) rear
with the regular type dates on one. Of course JMHO>Larry

[Larry M.]

Re: More Info On "Batch Built" Rare Options ON C2 Corvettes(66)

Here is one from Ebay with the conventional date format. https://www.ebay.com/itm/374157178206. However, the stamping appears to be "owner inspired". .

Larry

[Michael J.]

Re: More Info On "Batch Built" Rare Options ON C2 Corvettes(66)

What ratio is an "FC"?

[Larry M.]

Re: More Info On "Batch Built" Rare Options ON C2 Corvettes(66)

It is 4.56

[John F.]

Re: More Info On "Batch Built" Rare Options ON C2 Corvettes(66)

Here you go for the codes.

[John F.]

Re: More Info On "Batch Built" Rare Options ON C2 Corvettes(66)

Clearer picture.

[Mark F.]

Re: More Info On "Batch Built" Rare Options ON C2 Corvettes(66)

...As you can see it has "Julian Dates" stamped on it.(No Year Indicated) Of all the pictures I have accumulated through the years I HAVE NEVER SEEN A "FC" REAR END" with the normal "Year/Month/Date" on one. I have 3 to 4 pictures of "FC" rears and all have Julian dates on them. I believe that all these rears(FC) where "Batch Built" at some point
at the "W" plant thus the Julian date on them. Please> Someone prove my wrong and show me a (FC) rear
with the regular type dates on one. Of course JMHO>Larry

Larry,

Probably showing my ignorance here, but is the casting for a 4.56 rear end case the same as the lower (taller) ratios ?
Even if so, maybe they were assembled on a separate sub-line or area and used a different set of stamps ?

And I'm sure you know this - according to Noland Adams page 343, 91 4.56 ratios were produced in 1966 (5 with ECL UA; 86 with ECL QA). That's 1, 4.56 out of every ~305 other ratio codes produced for '66 Corvettes.

Man, that must be a real stump puller !

[Duke W.]

Re: More Info On "Batch Built" Rare Options ON C2 Corvettes(66)

There's an error in this listing. A little over halfway down, AR , "standard Wide ratio 4-speed...."

This is option G-91, which is an open diff. 3.08:1 axle ('62 RPO 203) that was available with the 250/300 HP engines with the four-speed option, and only the wide ratio was available for these engines from '62 to '65.

The first listing, AK, was standard with all transmissions for these two engines. The option is also incorrectly characterized in the '62, '63, and '64 axle code listings.

It's gone from the NCRS Spec Guide option listings after '65.

Duke

[Larry E.]

Re: More Info On "Batch Built" Rare Options ON C2 Corvettes(66)

Here is one from Ebay with the conventional date format. https://www.ebay.com/itm/374157178206. However, the stamping appears to be "owner inspired". .

Larry

Yes it does look a little suspicious but I am no stamp expert. Find it strange that in our 66 latest J/M it
does not say anything about the"Plant Stamp" as shown on my pictures. "W" is the Warren MI plant. This is clearly stated
in the "Corvette By The Numbers" by Alan Colvin.FYI Picture below is another "FC" Rear that HAS THE SAME JULIAN
DATE AS MINE>>033. Makes me wonder that my theory is correct. Larry

[Larry E.]

Re: More Info On "Batch Built" Rare Options ON C2 Corvettes(66)

Larry,

Probably showing my ignorance here, but is the casting for a 4.56 rear end case the same as the lower (taller) ratios ?
MARK: I DO NOT HAVE AN ANSWER FOR YOU ON YOUR QUESTIONS. MAYBE SOMEONE ELSE WOULD KNOW.

Even if so, maybe they were assembled on a separate sub-line or area and used a different set of stamps ?
MARK: THIS WOULD MAKE SENSE.

And I'm sure you know this - according to Noland Adams page 343, 91 4.56 ratios were produced in 1966 (5 with ECL UA; 86 with ECL QA). That's 1, 4.56 out of every ~305 other ratio codes produced for '66 Corvettes.
MARK; YES VERY RARE FOR SURE.

Man, that must be a real stump puller !

MARK: WOULD BE A VERY NASTY START FOR SURE. GLAD MY CAR IS NOW A "TRAILER QUEEN"; WOULD
NOT WANT TO PUT THIS TO A TEST; BUT SEE NO BETTER COMBO FOR PURE ACCELERATION!!JMHO>Larry
BTW>Jerry MacNeish who certified my 69 Z28 told me he tunned a pure stock L72 to "factory specs"and pulled 480 HP on his
friends dyno!!

[Dan A.]

Re: More Info On "Batch Built" Rare Options ON C2 Corvettes(66)

Because of the non typical for '66 build stamp format I have to wonder what the housing casting number and particularly the casting date are. I am not familiar with C3 dif build stamps but I'm aware the format and number of characters changed at least a couple of times during the 3rd generation. I do know that the FC code was also used for '68-9 big block 4.56 gear. Can C3 people shed some light on the above pictured stamps? And what are the casting numbers?