[A Rare 70]

Recently purchased a 64 GTO with a 389 - 4 barrel and 4 speed trans. The owner tells me that the engine is the original engine. It was rebuilt about 40 years ago and never started. My question is this, the block is a 9773155 block with what appears to be a 064 cast next to it. Is this the date code? If so, what does it translate to? My car appears to have been built the 2nd week of March in 64. The front stamping is a 78XW, the "W" looks to have been stamped after the 78X which I have read is normal. Any help would be appreciated. Thanks, Randy

[tom s]

4 speed GTO

[johnta1]

the block is a 9773155 block with what appears to be a 064 cast next to it. Is this the date code?

The '064' is probably the date code. But there should be a letter in the front of it. So check that the '0' might be a 'C'.
C64 - March 6, 1964?

[John V.]

In '64, the single digit days were cast as a single digit, so the 6th was a "6", not "06". Later Model Years the foundry began casting the day as 2 digits but not in the '64 Model Year.

Most likely you are reading a C64 cast date, ie. March 6, 1964.

It is possible that you are reading D64 (April 6, 1964) but assuming it is the original block it makes perfect sense to be C64.

I have an extensive log of '64 Engine Unit Nos. and Cast Dates. There is a very good correlation between cast dates and EUNs. The EUN essentially defines the calendar date that the Engine was assembled at Pontiac's only Engine Assembly Plant located at the home plant in Pontiac, Mich. With few exceptions, the cast date will be just ahead of the engine assembly date (not to be confused with the Time Built code of the Body Date Plate (trim tag). Using my log, the EUN gives me a very good indicator of the engine assembly date.

If you post the EUN from the front of the block, I can check it against my log. Most likely it will point to a block cast date of C64.

The 78X was stamped on the block by the Engine Assembly Plant. It meant the engine was the 4 bbl GTO 389 intended for a Manual Trans build.

The W was added at the Final Assembly Plant (where was your GTO built?) and the Final Plant was instructed to add certain Secondary Transmission Codes to the base Engine Code in accordance with specific options. The W indicates that the build included the optional Muncie wide ratio 4 spd along with a 3.08, 3.23, 3.36. or 3.55 rear axle. Most likely it would have gotten the standard content 3.23 rear unless it got A/C or unless a special order rear was specified.

The 3.90 axle required a different internal speedo drive gear inside the 4 spd for speedometer accuracy and when the 3.90 was optioned, the Secondary Trans Code was 9, same wide ratio Muncie but a 6 tooth speedo drive gear vs. 8 tooth. The trans itself also had a unique p/n but all that differed was the speedo gear on the mainshaft. Years ago, the Code 9 trans was believed to be a close ratio and references listed it that way. Proven wrong decades ago but references including PHS still mistakenly list the Code 9 as close ratio, it most definitely was not.

Very late in the '64 Model Year, Pontiac made the close ratio Muncie available in the GTO but only with Tripower and 3.90 (among other things). You could still get the Code 9 wide ratio with this combination but if you specified the close ratio, it got the Secondary Trans Code 8. The close ratio in a '64 was probably the rarest combination of any other option content you could think of save for maybe a Special Order Paint Color. In 30+ years of looking for them, I have only seen the close ratio documented for one '64 GTO.

If you have the PHS record for your GTO, the EUN will be on it UNLESS it was built at the Pontiac, Mich home plant. Unfortunately the Pontiac Plant PHS record does not show the EUN. If it was built at Fremont, Kansas City, or Baltimore, the EUN was recorded on the doc. The stamping on the block can be "matched" to the PHS although of course restorers know this too and restamped blocks make confirmation of original blocks much more difficult today.

[A Rare 70]

Thanks for the information. The car was built in Pontiac. The EUN is 344538

[John V.]

Perfect fit for an early March Engine Assembly Date so perfect fit for your 03B final assembly at the Pontiac Plant.

March 6, 1964 was a Friday.

You should take a close look at the cast date code. Besides confirming that the 1st character is a C, it is pretty common for 8's to be reported as 6's and vice versa and 5's to look like 6's and vice versa. Same way a C can look like an O or 0. So could be C54 or C84 if not C64. Any of these would be possible for your EUN.

But regardless, EUN 344538 can never be challenged as being original to your GTO. Without the Ident-O-Plate or some other documentation there is no way to confirm it but there is also no way for anybody to doubt it.

Enjoy your GTO!

[A Rare 70]

Attached is a pic of the date code. Looks like it may have started life as a “C” but become damaged somewhere.

[John V.]

The letter in the cast date code does seem a bit strange but could simply be the result of some sort of damage.

Can't say that I've committed to memory what the p/n characters should look like but when I first looked at the pic, it was the first 2 digits, the 97, of the p/n cast on the block that struck me as strange. But after looking at pix of another '64 389 block showing the same anomaly, I figure it must be correct for at least one of the patterns used by the foundry to cast '64 blocks.

Unless the code pad on the front of the block shows grinding marks that are evidence that the original stampings were removed, I think you can be confident you have your GTO's born with block.

[A Rare 70]

Thank you John for all of your information and feedback on this matter. I have found the original Pontiac Ident-O-Plate for my car and it has the EUN number listed on it. Since the car has sat for over 40 years I was fairly sure that the engine was the original, as stated by the owner, but due to the issue with the casting date I was curious. Now I am sure that it is original since the front pad of the engine has not been disturbed and all number match. Thanks again for your help on this matter.