# "66 Engine ID



## histoy (May 22, 2019)

I'm a little confused about our engine. The VIN number of the '66 GTO is 242176. The front of the engine is stamped 248916 YS. I believe the YS indicates that the engine was built for a '66 GTO with a 4 barrel carb, but it's not the "born with" engine for our car. Our GTO does have a 4 barrel carb. The other thing that seems strange is the capacity of the oil pan is only 4 qts. I believe that the '66 engine should have a 6 qt. capacity. 4 qt. oil pans were used from '61 -'64. Am I correct?


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## Old Man Taylor (May 9, 2011)

The oil capacity should be 5 quarts, 6 with the regular sized filter. Pontiac made the same pan for 4 and 5 quarts, they just put in a different dip stick. Your YS engine code could be any thing from a 1965 to a 1978 engine. The only year it wasn't a 389 or 400 was '74. You can get closer by looking at the head casting number, but the better way is to look at the date code on the back of the block by the distributor. If it has 3 freeze plugs on each side of the block then it is 67-up.


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## histoy (May 22, 2019)

Thanks for your help.


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## histoy (May 22, 2019)

I checked the engine date code and it shows L I66 so that shows it was cast in 1966. Again, thanks for your help.


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## Old Man Taylor (May 9, 2011)

It's late enough in 66 that it would have gone into a 67 model year.


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## PontiacJim (Dec 29, 2012)

histoy said:


> I checked the engine date code and it shows L I66 so that shows it was cast in 1966. Again, thanks for your help.


X2 that the engine was cast L=December 1966 and would be a 1967 engine. YS seems to be the 335HP engine. Should have the 3 freeze plugs on the side of the block and the engine casting number is up near the distributor which will also indicate a 1966/early 1967 engine. 1966 389 will have casting number 9778789. Later 1967 400 will have casting number 9786133 and it is on the passenger side back of the block below the head on the block "shelf." You can see the transmission alignment dowel in the photo. They began putting them here in late 1967 in preparation for the 1968 and up block casting location.


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## histoy (May 22, 2019)

Thanks for your help. I'll have to check it out to see the casting number.


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## histoy (May 22, 2019)

The casting number is 9778789 so it is a 389 engine. Thanks for your help Pontiac Jim.


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## PontiacJim (Dec 29, 2012)

histoy said:


> The casting number is 9778789 so it is a 389 engine. Thanks for your help Pontiac Jim.



OK, 9778789 is 1966, 2 freeze plugs on the side of the block is 1966, code YS is 1966 335HP/automatic, heads should be the "093" for 1966.

So the only thing wrong is the casting date. The "L" may be something else like perhaps poorly cast? Maybe a "D" "E"? The transition from year to new model year is typically August and engines cast from August on are for the next model year with the new models hitting the showroom floors in September, so an "L" would fall into the 1967 model year.

But, it could be possible that it may be a replacement block? Pontiac did some strange things. Could have been a 389 block cast in December as a replacement block. No expert on this, but if a dealer needed one for warranty, and with the introduction of the 400CI, maybe a run of 389 cores were cast just for warranty purposes. Just a guess. Pontiac did do runs like this to have parts on hand for warranty. Later blocks were stamped SR(Service Replacement) and had a production serial number.

My brother has a replacement 1967 400CI block. No EUN number or engine code. It is however stamped with a "P" for the Pontiac foundry.


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## histoy (May 22, 2019)

I checked and both heads are 93 castings.


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## Old Man Taylor (May 9, 2011)

They're '66 heads on a '67 block.


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## johnta1 (Mar 18, 2020)

Can you take a picture of the date code?


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## histoy (May 22, 2019)

I tried several ways, but I can't get a picture back there under the distributor. Here's what it looks like. (@) is a screw. @L [email protected] The gap between the L & I is actually 3 times longer than what's shown here, but the computer program closes the gap when I preview and save it.


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## Gtowally (Jan 19, 2019)

Old Man Taylor said:


> They're '66 heads on a '67 block.


You can’t put 66 heads on a 67 block. 66 pushrods are too short, 67 pushrods are too long


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## Jerry H. (Mar 19, 2020)

histoy said:


> I'm a little confused about our engine. The VIN number of the '66 GTO is 242176. The front of the engine is stamped 248916 YS. I believe the YS indicates that the engine was built for a '66 GTO with a 4 barrel carb, but it's not the "born with" engine for our car. Our GTO does have a 4 barrel carb. The other thing that seems strange is the capacity of the oil pan is only 4 qts. I believe that the '66 engine should have a 6 qt. capacity. 4 qt. oil pans were used from '61 -'64. Am I correct?


Just curious, how have you determined that it is not the 'born with' engine? You understand that the # stamped by the YS has absolutely nothing to do with the VIN or data plate.


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## johnta1 (Mar 18, 2020)

> I tried several ways, but I can't get a picture back there under the distributor.


I was wondering if the last '6' is misread possibly a '5'?
(easy to misread them)

What is the date from the cowl tag?


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## histoy (May 22, 2019)

No, I didn't understand that the numbers stamped on the front of the engine had nothing to do with the VIN or data plate. I'm surprised that they don't. If they don't match, I don't know how you can tell if it's the born with engine. The date on the data plate is 12D The second 6 might be a five, but I guess I'd have to do a pencil etching when I have the distributor out to verify.


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## Old Man Taylor (May 9, 2011)

Gtowally said:


> You can’t put 66 heads on a 67 block. 66 pushrods are too short, 67 pushrods are too long


Who said they're stock pushrods? Maybe he read the date on the block wrong. I've mixed and matched blocks and heads a lot, but I've always had pushrods made to get the geometry as close as I can.


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## Old Man Taylor (May 9, 2011)

You can't tell if the engine is original to the car. All you can do is see that the engine code matches the original configuration, and that it has a cast date before the build of the car. Typically about 3 weeks.


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## johnta1 (Mar 18, 2020)

> The date on the data plate is 12D The second 6 might be a five, but I guess


That would fit if the 6 is being misread and the last digit is a 5. (12-16-65)


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## johnta1 (Mar 18, 2020)

A page on the Engine Unit Number
Engine Unit Number


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## histoy (May 22, 2019)

Could someone tell me what the date of 12D means?


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## johnta1 (Mar 18, 2020)

The car went down Fisher assembly during 4th week of December, basically.


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## histoy (May 22, 2019)

I see from the link that you provided there is a partial VIN number on the block by the lower radiator hose. I'll see if I can find a number there. If it's there, and visible, that would tell me if it's the born with engine.


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## johnta1 (Mar 18, 2020)

Unfortunately, that doesn't apply to your engine. It started in 1968 years.


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## PontiacJim (Dec 29, 2012)

histoy said:


> I see from the link that you provided there is a partial VIN number on the block by the lower radiator hose. I'll see if I can find a number there. If it's there, and visible, that would tell me if it's the born with engine.


X2 with johnta1. If you have a partial VIN, that is where they would be stamped on 1968 and up engines per federal regulations, UNLESS, again, it may be a replacement block and stamped by a dealer or begins with the letters "SR".

You have yet to let us know if the engine has 2 or 3 freeze plugs on the block where the engine mounts are? Later blocks will also have the cubic inch cast on them near front/side while you are under there.


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## histoy (May 22, 2019)

The engine has 2 freeze plugs per side. If I'm misreading the cast date and it's actually @L [email protected] then does the assembly date of 12D make sense? I'm sorry that I'm so ignorant about these things, but I'm trying to understand more about Pontiacs. My Dad owned several and I learned to drive in a '60 Catalina. The only other Pontiac I've owned was an '81 Firebird.


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## Old Man Taylor (May 9, 2011)

Yes December 16, 1965 is definitely an engine for the '66 model year.


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## Old Man Taylor (May 9, 2011)

If the 12D is on your VIN tag it represents the 4th week in December.


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## PontiacJim (Dec 29, 2012)

histoy said:


> The engine has 2 freeze plugs per side. If I'm misreading the cast date and it's actually @L [email protected] then does the assembly date of 12D make sense? I'm sorry that I'm so ignorant about these things, but I'm trying to understand more about Pontiacs. My Dad owned several and I learned to drive in a '60 Catalina. The only other Pontiac I've owned was an '81 Firebird.


OK, we have a winner! December 16, 1965 makes it a 1966 engine. Whew, glad that's all settled.


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## Old Man Taylor (May 9, 2011)

Your dates match well enough that the block might be the original. If not, someone did a good job picking one for the replacement.


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## histoy (May 22, 2019)

Thank you.


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## chief65 (Jun 6, 2011)

Did you get the protector-plate with your 66 GTO?
If so, look and see what the engine number is on the protecto- plate. It might match the number on your engine block and bingo, you have proof that it is the born with motor.


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## histoy (May 22, 2019)

No, I don't have the protecto-plate.


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## BearGFR (Aug 25, 2008)

histoy said:


> ... If they don't match, I don't know how you can tell if it's the born with engine....


You can't, not until they started also stamping a partial VIN on the front of the block down low, passenger side, adjacent to the timing cover --- which didn't start until after '66. '('68 maybe? I'm too lazy to go look that up right now  ) That YS will tell you additional information, such as what body style it was originally installed in, carburetor, cam, transmission, etc. -- but only after you've gotten a positive ID on the model year and block casting. That's because the same 2-character "engine code" was reused in multiple years and meant different things depending on the year. There's one shot you've got to find out if it's the 'born with' engine, and that's using the digits you found by that "YS" stamp. That's the engine build serial/sequence number and -sometimes- (not always) PHS will have a record of it associated with your VIN. You might get lucky, but don't bet the farm on it. 
Getting a positive ID on the block always has to start with getting the correct date code, then using the block casting number for that model year. Remember the engine foundry started casting for the next model year at "about" the middle of the previous year (the actual cutover date moved around some, depending on inventory, sales, projected demand, etc ).

Bear


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