# 1966 GTO - Numbers matching?



## GTOKurt (Jan 28, 2017)

I need some help and advice.

I have a 1966 GTO, bought just a few years ago. The prior owner stated it had a non-numbers matching engine - something from a 69 Pontiac Firebird. He may have been wrong.

Recently, I had some motor problems, and some white smoke out a tailpipe. I pulled the heads and found lots of problems, including mismatched/worn pushrods and worn lifters. I have not yet ruled out a problem in the block, but I noticed that maybe this car did have its original motor. The original tranny is long gone, and was replaced with a TH350. 

I plan to look into the block and pistons to make sure the block is OK. Regarding looking into the block, is there an "easy" way to pull the oil pan so I can look into the block from below? I do not want to pull the engine out unless I plan to replace it.

So I am trying to decide if I should rebuild the old heads, or buy a new set of Edelbrock heads, or just get a whole "new" rebuilt motor. Knowing if the numbers match will lead me to repairing versus replacing to entire motor.

Here are the numbers and codes:
VIN: 242 676 P 322zzz
Block code: YS (with two freeze plugs per side)
Engine code: 778789 (not 9778789) with date code: F 16 (June 1, 1966)
Heads code: 092 
PHS states an invoice date of 6/7/1966

Can anyone tell me if I have a numbers-matching car/motor?

Any help or advice is greatly appreciated.


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## PontiacJim (Dec 29, 2012)

GTOKurt said:


> I need some help and advice.
> 
> I have a 1966 GTO, bought just a few years ago. The prior owner stated it had a non-numbers matching engine - something from a 69 Pontiac Firebird. He may have been wrong.
> 
> ...


PHS documents should provide the block code. 

Sounds like it could be an original engine. Here are block codes for 1966: Pontiac Engine Codes

Here are head codes for 1966: Pontiac V8 Cylinder Heads

It could be the original block with the YS code seeing it has the 2 freeze plugs, but the GTO's used the 093 heads, not the 092 heads. The blocks did not have VIN numbers stamped on until 1967/1968. You should see an Engine Unit Number above the letter code. This is a sequence number used by Pontiac. Your PHS documents should have highlighted this for you.

The engine casting number looks correct for 1965-66 even with the missing "9". Here is more info to go through on the ID of your car: https://classicregister.com/id-guides/how-identify-1966-pontiac-gto-coupe-hardtop-convertible

Now tell me how you are going to check the condition of the rings/ring lands/pistons by pulling the pan and "looking inside." Seems the previous owner did not know what the engine was, so I would not assume that the engine is in good shape at all without a total disassembly for inspection and then go from there. Don't throw good money on top of bad. :thumbsup:


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## GTOKurt (Jan 28, 2017)

Jim,

Thanks for the help. PHS says block code is YS. 

The engine unit number is not fully legible. See pic. It looks like the number was never stamped deeply into the metal (or it was somehow wiped away, but the paint does not appear to be thick. The area just looks very smooth.

I have read about others in this forum who have the same missing '9' with the same engine casting number that I have: "778789".

My plan to inspect the block from underside is to pull the oild pan, then push the pistons up and out of the block to inspect the cylinder walls, rings and pistons. Your thoughts about doing a full inspection in light of the info from the previous owner is appropriate, and I am just looking for an alternative to pulling the entire motor.

Assuming the block and pistons check out OK, should I rebuild the heads, or get new heads like Edelbrock's, or look for a matched rebuilt set?

If the block is bad, then I might as well get a new engine. If it is just bad rings or pistons, then keeping the original block in tact makes sense.


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## cij911 (Oct 25, 2017)

I believe you have to pull the motor to get the pan off....Sorry.


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## PontiacJim (Dec 29, 2012)

GTOKurt said:


> Jim,
> 
> Thanks for the help. PHS says block code is YS.
> 
> ...


Looking at the photo, someone has messed with the engine code and restamped it "YS". So with the 092 heads, it is most likely an engine out of a full size car.

To better answer your question, you need to know what kind of a budget you plan on spending and how much HP at what RPM band. Pontiac's are built for torque.

You can't put Edelbrock heads or any large valve head on a 389. The later 1967 and up valves are angled differently and repositioned more to center. So piston valve reliefs will not match and the valves may hit the cylinder wall if not notched.

You can bore a 389 to that of a 400CI and then go from there with 400CI top end if you want Edelbrock heads or big valve heads. Or you can stick with the 389 and keep the 092 heads and use that as your base.

Many options and ways to build your engine. If you do a search using the upper right hand "Google Custom Search" and type in 389 build, 389 engine, 389 to 400, 092/093 heads, etc., you will pull up past posts from this site that should give you plenty of ideas. Again: budget, power range, and parts matching to make it all work. Keep in mind that as you build bigger HP/TQ, that the rest of your driveline may not handle it and things behind the engine will break or need upgrading and that adds $$$. And as *cij911* stated, you really want to pull the engine as the pan typically does not come off while in the car, but if you tear off the heads, pull the distributor, pull the radiator, and undo the engine mounts, you may get lucky enough to lift the engine high enough and drop the pan without a complete removal of the engine. :thumbsup:


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## GTOKurt (Jan 28, 2017)

PontiacJim said:


> Looking at the photo, someone has messed with the engine code and restamped it "YS". So with the 092 heads, it is most likely an engine out of a full size car.


So if the block has been re-stamped (I agree, it looks like a bad and ill-intentioned forgery / re-stamping), how to explain the engine code of '778789', which others on this forum also have. 

... I think I get it now. The 778789 was both a GTO and a big car engine. other than the head numbers of 092 or 093, what differences exist between the two types og '778789' blocks? I see from the table the HP ratings are significantly lower. I also see the vale sizes of 092 and 093 are the same, as well as the compression ratio.


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## PontiacJim (Dec 29, 2012)

GTOKurt said:


> So if the block has been re-stamped (I agree, it looks like a bad and ill-intentioned forgery / re-stamping), how to explain the engine code of '778789', which others on this forum also have.
> 
> ... I think I get it now. The 778789 was both a GTO and a big car engine. other than the head numbers of 092 or 093, what differences exist between the two types og '778789' blocks? I see from the table the HP ratings are significantly lower. I also see the vale sizes of 092 and 093 are the same, as well as the compression ratio.


The casting number on the block only ID's it as a 1965/66 year block, no more, no less. It is the block letter code and heads that ID what the engine went into, HP, cam, carb, manual/automatic trans along with the date build code the engine was cast. I also think the EUN number can match the engine to the original car it was installed into and might be found on the PHS documents. 092 and 093 are the same basic casting except 092 has a 70 cc chamber for an advertised compression of 10.5 while the 093 has a 68 cc chamber for an advertised compression of 10.75.


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