# '67 YS block mystery



## Massrog (Apr 20, 2018)

Hello, I am new here and hope you folks can help me with my mystery engine. I am the proud owner of a '67 but not a GTO. Mine is a Firebird which was sold to me as having the original engine. Obviously that is not the case but this is the mystery... The block has no VIN on it anywhere. The engine code is 513768 with the YS under it. Nobody on any forum I have asked has any idea how an unmarked block got into my car. Was it possible for someone back then to purchase a GTO engine to swap into a 400 Firebird and have it not be a "service replacement" or otherwise associated to a specific car? I did read somewhere that certain dealers were doing swaps for some customers if this is one of those would the block be unmarked like this? Any help would be Greatly appreciated!!!
Thanks,
RogerG


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## PontiacJim (Dec 29, 2012)

VIN numbers were not added until 1968. You can verify it to be a '67 block by looking by the distributor hole. The casting number for '67 400 blocks is 9786133 with the distributor hole taking out the "97." However, if it is a late 1967 block (as I recall cast after May), the 9786133 will be found on the block ledge behind the right head where the trans bolts up like all 1968 and up blocks - so this can help ID block casting time frame. Also, your block casting date codes will be found there - a letter and 3 digits. Assume heads have already been identified and the date codes?

The number you see is the Engine Unit Number and not related to the VIN. 

Ton of info here at this website: Codes ?- First Generation Firebird (1967, 1968, 1969)


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## Shake-N-Bake (Jun 16, 2015)

Massrog said:


> Hello, I am new here and hope you folks can help me with my mystery engine. I am the proud owner of a '67 but not a GTO. Mine is a Firebird which was sold to me as having the original engine. Obviously that is not the case but this is the mystery... The block has no VIN on it anywhere. The engine code is 513768 with the YS under it. Nobody on any forum I have asked has any idea how an unmarked block got into my car. Was it possible for someone back then to purchase a GTO engine to swap into a 400 Firebird and have it not be a "service replacement" or otherwise associated to a specific car? I did read somewhere that certain dealers were doing swaps for some customers if this is one of those would the block be unmarked like this? Any help would be Greatly appreciated!!!
> Thanks,
> RogerG


Manual trans car?
I have a 67 WZ engine that I might be willing to sell.

Like Jim said.....no VIN on 1967 blocks. There might be an Engine Unit Number listed on the PHS docs. What is that number?


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## Massrog (Apr 20, 2018)

PontiacJim said:


> VIN numbers were not added until 1968. You can verify it to be a '67 block by looking by the distributor hole. The casting number for '67 400 blocks is 9786133 with the distributor hole taking out the "97." However, if it is a late 1967 block (as I recall cast after May), the 9786133 will be found on the block ledge behind the right head where the trans bolts up like all 1968 and up blocks - so this can help ID block casting time frame. Also, your block casting date codes will be found there - a letter and 3 digits. Assume heads have already been identified and the date codes?
> 
> The number you see is the Engine Unit Number and not related to the VIN.
> 
> Ton of info here at this website: Codes ?- First Generation Firebird (1967, 1968, 1969)


Thanks very much Jim and S-N-B I thought I'd finally found the right group! The date code for the block is D117 and the heads are 670's but I couldn't locate the date code on those. I think Jim you ID'd the 513768 YS as the unit number correct?


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## Shake-N-Bake (Jun 16, 2015)

Is your car an automatic California Air Injection car? If so, I would investigate the original engine idea a bit more. Did you order the PHS docs? If so, check the number in the Engine Unit Number box to see if it matches the stamped numbers on the block (above the YS). If that number matches, then you have the original engine. YS (GTO) and XN (Firebird 400) are very similar engines. Same compression, cam, distributor etc......the LH exhaust manifold and oil filter housing are the two differences that I can think of (there are likely other small differences as well...).

I believe there are a very few documented cases where the incorrect 2 letter code was stamped on the front of the engine so further investigation is warranted.

The cast date on the 679 heads can be found under the valve covers.


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## PontiacJim (Dec 29, 2012)

Agree with Shake-N-Bake. The Pontiac Historical Society documents for your car should have the build info and the EUN you see above the block code of YS - 513768. The block date you provided shows the block cast as April 11, 1967. The "670" heads are correct for your engine block code, YS. The YS code indicates a 335 HP 400, automatic, found in the Tempest/GTO body. It is likely that someone may have attempted to replace the original engine with a like engine from 1967. The 1967 Firebird 400 engines were all rated at 325 HP, to include the Ram Air engines, which of course were much higher in HP. 

To limit the HP in the Firebird, from what I read, the opening of the secondaries on the Q-jet was limited with a stop so they could not open fully, turning the 750CFM carb into a 650CFM carb - thus making for a lower HP rating on the lighter Firebird body to meet the power-to-weight requirements. This limiter on the Q-jet seems to be controversial as to its existence/use. I have had Q-jets that did have this small flat metal arm that was activated by the choke opening and locked the secondary air valve flap and prevented it from opening when the car was cold. As the engine warmed, choke opened, it moved this small little arm up out of the way for operation of the secondary air flap. It was easily removed and I think this may be the "mystery" limiter often spoke of.

The Firebird and GTO have different carb numbers. I did find this mention of it on another forum, "The air valve limit lever may be unique to the Q-jet used on the 1967-1969 Firebird 400 in order to stay within the GM 1-horsepower to 10 lb. weight limit for insurance purposes.

"Air Valve Lock Out Lever" ... GM Part number: 7031393

That lever restricts the opening of the secondary air valve to 90% in order to maintain the General Motors front office horsepower requirement of 10 lb. per 1 HP, for insurance purposes.

For example: 1967-1969 Firebird 400 CI engine, rated at 325 HP and 3250 lb. curb weight. That engine was identical to a 1968-1969 GTO 400 CI engine, rated at 350 HP and 3506 lb. curb weight. The Q-jet on the 1968-1969 GTO did not receive the Q-jet with the Secondary Air Valve Lock Out lever."

Correct carb numbers for the Firebird 400 (excluding Ram Air engines) were 7027273, 7037273, & 7027272. This might be something else to check. Number is stamped on vertical side of carb near the linkage. 

With Pontiac, never say never and it is possible that the engine was installed as factory somehow or mis-stamped, but the PHS documents would be the official word on this. You can read more here: PHS Automotive Services, Inc.


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## Massrog (Apr 20, 2018)

I checked my PHS and the EUN is 415348 YT. The car was built first week of March so the engine is definitely a replacement of some sort. I have a copy of the Craigslist ad that was placed by the second owner who sold it to the guy who restored it and he states orig. engine (for what that's worth). I guess that either it was a simple replacement somewhere along the line or with the dates a month off it may be one of those "dealer swaps". The car was sold and spent all of it's life within 60 miles of it's birthplace until 2009 and Grabski in Cleveland was one of the performance oriented dealers I think. Maybe someone here can provide info on them.


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## PontiacJim (Dec 29, 2012)

Massrog said:


> I checked my PHS and the EUN is 415348 YT. The car was built first week of March so the engine is definitely a replacement of some sort. I have a copy of the Craigslist ad that was placed by the second owner who sold it to the guy who restored it and he states orig. engine (for what that's worth). I guess that either it was a simple replacement somewhere along the line or with the dates a month off it may be one of those "dealer swaps". The car was sold and spent all of it's life within 60 miles of it's birthplace until 2009 and Grabski in Cleveland was one of the performance oriented dealers I think. Maybe someone here can provide info on them.


Well, the PHS documents settle it. The engine is not the original one. YT is indeed a Firebird engine code with automatic as built from the factory and the EUN isn't even close to your original documents. That said, the engine has been swapped into your car at some point and it is an original 1967 engine, just not the correct one for your car, period.

If the engine had been replaced by a dealership due to a warranty issue, it would not have had a block code on it. My brother has a 1967 replacement block for what we believe is a GTO (670 heads) and it is stamped with a "P" for Pontiac where the blocks were cast. In 1968, this, along with VIN number requirement, was changed in that service replacement blocks/engines were to be restamped with the original VIN numbers.

So again, the engine is not the original one to that car, but is a correct 1967 engine for that year out of a GTO. It would be interesting to email PHS and see if it is at all possible to match up the EUN with the GTO it came out of or a close time frame when it could have been installed in a GTO.


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## Massrog (Apr 20, 2018)

If I wanted to put together a date correct YT engine would the head date and block date need to match? Do you know how much older the block needs to be to be "correct" for my car? Would a proper firebird engine increase the overall value of the car? I can source a block that is a couple of weeks earlier than the car and heads a few months earlier (end of '66). Is that a decent start or just stand pat? Looking forward to your thoughts!


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## BearGFR (Aug 25, 2008)

On the "power limit feature" that was present on some Firebirds, my understanding is that it was accomplished by limiting how far the secondary throttles were allowed to open ("bottom" --- not the air valve on top of the carb). Check it by getting to where you can observe the position of the secondary throttle blades (remove the air cleaner and hold the air valve open while you operate the throttle linkage by hand, or pull the carb and do it on a workbench). If the secondary throttle blades don't rotate to vertical (actually very near vertical and not perfectly vertical - the correct angle is shown in Cliff Ruggles's book) then there's an adjustment in the form of a bend point on the link that connects the to the primary throttle shaft. 

The air-valve lockout part on top of the carb is connected to the choke linkage and is intended to prevent the air valve from opening whenever the choke is applied - presumably on a cold engine with an automatic choke. The other control on the air valve is the linkage to the vacuum diaphragm on the front of the carb. At part throttle (high vacuum) conditions it too holds the air valve shut, along with the spring tension on the air valve shaft itself. Whenever manifold vacuum drops (like when you hang your right big toe over in the carburetor), the diaphragm has a calibrated orifice in it that controls how quickly the vacuum bleeds off and relaxes that linkage - thus it works in conjunction with the spring tension to control how quickly the air valve can open. If it doesn't open 'fast enough' you're leaving power on the table. If it opens too rapidly, you get the bog that people 'blame' on QJets. This is also the mechanism that leads people to mistakenly believe that their secondaries aren't opening. They think this because with the car sitting in the driveway in neutral, the air valve doesn't open when they whang on the throttle. What they don't understand is that it's not possible to create the 'low manifold vacuum' condition necessary for the diaphragm to relax and allow them to open for more than a fraction of a second this way with the car in neutral because there's no load on the engine. QJet "trick of the month club" life members will recommend disabling this mechanism completely and loosening the air valve spring tension to the point where a mosquito landing on the air valve will flop it open, and that's exactly what CAUSES the infamous QJet bog. It creates a condition where the air valves will dump a huge gulp of air into the secondaries long before there's enough flow velocity present to cause the carb to supply the fuel needed to go with it - causing the bog. The right way to optimize the air valve opening rate is to adjust both the spring tension and the bleed-off rate in the diaphragm so that the air valve is allowed to open as quickly as the engine is able to handle _and not one bit faster_. This is a trial and error process that has to be tailored to each individual engine and changes depending on the combination of engine displacement and cam profile --- the things that control how efficiently the engine functions as an air pump at various RPM. I dialed mine in by first drilling out the orifice in the diaphragm and making it way too big (effectively disabling the diaphragm), then taking a few short sections of brass tubing, completely plugging them with epoxy, and using very small wire drills to drill an orifice hole in the epoxy plug. I spliced one piece of the epoxied tubing into the vacuum line coming off the diaphragm and started testing -- gradually drilling the hole larger until I found the point where it got 'too fast' and I started getting the bog, then I made a second 'orifice tubing' and drilled it to the size the previous one had been before I started getting the bog. I expect to have to go through that process again with the new build because of the different cam profile this time - if I don't decide to jump ship and go to a brand H carb - the engine is to the point where even 800 cfm 455SD Qjet isn't quite enough to feed it. 

Bear


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## PontiacJim (Dec 29, 2012)

BearGFR said:


> On the "power limit feature" that was present on some Firebirds, my understanding is that it was accomplished by limiting how far the secondary throttles were allowed to open ("bottom" --- not the air valve on top of the carb). Check it by getting to where you can observe the position of the secondary throttle blades (remove the air cleaner and hold the air valve open while you operate the throttle linkage by hand, or pull the carb and do it on a workbench). If the secondary throttle blades don't rotate to vertical (actually very near vertical and not perfectly vertical - the correct angle is shown in Cliff Ruggles's book) then there's an adjustment in the form of a bend point on the link that connects the to the primary throttle shaft.
> 
> The air-valve lockout part on top of the carb is connected to the choke linkage and is intended to prevent the air valve from opening whenever the choke is applied - presumably on a cold engine with an automatic choke. The other control on the air valve is the linkage to the vacuum diaphragm on the front of the carb. At part throttle (high vacuum) conditions it too holds the air valve shut, along with the spring tension on the air valve shaft itself. Whenever manifold vacuum drops (like when you hang your right big toe over in the carburetor), the diaphragm has a calibrated orifice in it that controls how quickly the vacuum bleeds off and relaxes that linkage - thus it works in conjunction with the spring tension to control how quickly the air valve can open. If it doesn't open 'fast enough' you're leaving power on the table. If it opens too rapidly, you get the bog that people 'blame' on QJets. This is also the mechanism that leads people to mistakenly believe that their secondaries aren't opening. They think this because with the car sitting in the driveway in neutral, the air valve doesn't open when they whang on the throttle. What they don't understand is that it's not possible to create the 'low manifold vacuum' condition necessary for the diaphragm to relax and allow them to open for more than a fraction of a second this way with the car in neutral because there's no load on the engine. QJet "trick of the month club" life members will recommend disabling this mechanism completely and loosening the air valve spring tension to the point where a mosquito landing on the air valve will flop it open, and that's exactly what CAUSES the infamous QJet bog. It creates a condition where the air valves will dump a huge gulp of air into the secondaries long before there's enough flow velocity present to cause the carb to supply the fuel needed to go with it - causing the bog. The right way to optimize the air valve opening rate is to adjust both the spring tension and the bleed-off rate in the diaphragm so that the air valve is allowed to open as quickly as the engine is able to handle _and not one bit faster_. This is a trial and error process that has to be tailored to each individual engine and changes depending on the combination of engine displacement and cam profile --- the things that control how efficiently the engine functions as an air pump at various RPM. I dialed mine in by first drilling out the orifice in the diaphragm and making it way too big (effectively disabling the diaphragm), then taking a few short sections of brass tubing, completely plugging them with epoxy, and using very small wire drills to drill an orifice hole in the epoxy plug. I spliced one piece of the epoxied tubing into the vacuum line coming off the diaphragm and started testing -- gradually drilling the hole larger until I found the point where it got 'too fast' and I started getting the bog, then I made a second 'orifice tubing' and drilled it to the size the previous one had been before I started getting the bog. I expect to have to go through that process again with the new build because of the different cam profile this time - if I don't decide to jump ship and go to a brand H carb - the engine is to the point where even 800 cfm 455SD Qjet isn't quite enough to feed it.
> 
> Bear



Bear, I think you missed the point of the OP's question, BUT, good post. He is trying to ID his engine and the carb was just another nugget in doing that. It is not the correct engine as it turns out. :thumbsup:


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## PontiacJim (Dec 29, 2012)

Massrog said:


> If I wanted to put together a date correct YT engine would the head date and block date need to match? Do you know how much older the block needs to be to be "correct" for my car? Would a proper firebird engine increase the overall value of the car? I can source a block that is a couple of weeks earlier than the car and heads a few months earlier (end of '66). Is that a decent start or just stand pat? Looking forward to your thoughts!




This is my opinion. Why bother? The block code will match the car, but the EUN won't unless you plan on doing something illegal like restamping it to pass it off as original. The next buyer will have access to the same PHS documents you have and that won't change the EUN number on the documents.

I personally don't think the original block code/date coded engine will add a significant valve (without the correct EUN) to the car unless it had a lot of special options, was a 1 of 5 car, or was super low original miles and never restored. Then of course all other engine components/drivetrain would have to be correct casting/ID numbers to match. The GTO engine represents the correct year and has more HP per say, so not really a loss there. You would probably increase value if you added a 461 stroker kit, better cam, prepped the heads, RA exhaust manifolds, duals, and added a Tremec 5-speed and Ford 9" with 3.89 gearing..........or the popular with the new generation LS3 swap. 

So it will never be "original" again and from there, value will be based on the future buyer who sees his dream in the car.


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## BearGFR (Aug 25, 2008)

Yeah, probably. I'm olde and getting senile - sometimes I ramble... ?

Bear


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## PontiacJim (Dec 29, 2012)

BearGFR said:


> Yeah, probably. I'm olde and getting senile - sometimes I ramble... ?
> 
> Bear


Love ya, man. LOL :thumbsup:


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## Massrog (Apr 20, 2018)

PontiacJim said:


> VIN numbers were not added until 1968. You can verify it to be a '67 block by looking by the distributor hole. The casting number for '67 400 blocks is 9786133 with the distributor hole taking out the "97." However, if it is a late 1967 block (as I recall cast after May), the 9786133 will be found on the block ledge behind the right head where the trans bolts up like all 1968 and up blocks - so this can help ID block casting time frame. Also, your block casting date codes will be found there - a letter and 3 digits. Assume heads have already been identified and the date codes?
> 
> The number you see is the Engine Unit Number and not related to the VIN.
> 
> Ton of info here at this website: Codes ?- First Generation Firebird (1967, 1968, 1969)





PontiacJim said:


> This is my opinion. Why bother? The block code will match the car, but the EUN won't unless you plan on doing something illegal like restamping it to pass it off as original. The next buyer will have access to the same PHS documents you have and that won't change the EUN number on the documents.
> 
> I personally don't think the original block code/date coded engine will add a significant valve (without the correct EUN) to the car unless it had a lot of special options, was a 1 of 5 car, or was super low original miles and never restored. Then of course all other engine components/drivetrain would have to be correct casting/ID numbers to match. The GTO engine represents the correct year and has more HP per say, so not really a loss there. You would probably increase value if you added a 461 stroker kit, better cam, prepped the heads, RA exhaust manifolds, duals, and added a Tremec 5-speed and Ford 9" with 3.89 gearing..........or the popular with the new generation LS3 swap.
> 
> So it will never be "original" again and from there, value will be based on the future buyer who sees his dream in the car.


Yeah I suppose a purist wants pure and anyone else just wants to pay for what he thinks it's worth. As to any further mods.. I don't think so unless it's to move the seat track back to accommodate my 50 something fat a--! Those LS's may run better for daily or extended driving but it's not a classic to me. It's my bucket list car from when as a teen I read a Hot Rod article on a shootout between a big block Mustang, 396 Camaro, Hemi Cuda, an AMX and as an after thought the 400 Firebird all stock. As a Camaro owner I was amazed the Firebird came out on top (by quite a bit)! I decided then and there I would own a 400 Firebird before I die and this one's it


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## PontiacJim (Dec 29, 2012)

Massrog said:


> Yeah I suppose a purist wants pure and anyone else just wants to pay for what he thinks it's worth. As to any further mods.. I don't think so unless it's to move the seat track back to accommodate my 50 something fat a--! Those LS's may run better for daily or extended driving but it's not a classic to me. It's my bucket list car from when as a teen I read a Hot Rod article on a shootout between a big block Mustang, 396 Camaro, Hemi Cuda, an AMX and as an after thought the 400 Firebird all stock. As a Camaro owner I was amazed the Firebird came out on top (by quite a bit)! I decided then and there I would own a 400 Firebird before I die and this one's it



Beautiful car. I had a 1967 Firebird, my first intro into "fast" as my 1956 Pontiac was my first car. It was red with red interior, bucket seats, console, 3 speed on the floor, and the original 326 had been replaced with a later 350CI that had been warmed up a bit. The paint was faded and the body had a big dent in the drivers front fender where the previous owner had kicked it after losing a circle track race at Thompson Speedway in Connecticut. The interior was still in good shape. Paid $300 for it. That was about 1978-79ish and I was 19. It would burn the tires pretty easily and it was fast and a blast to drive with the three speed. It had a bad rear seal leak and I pulled the engine and re-gasketed the engine to cure the leaks. I think I kept it about a year and sold it and heard through the grapevine that the new owner had totaled it out on a tree. Was a great car and the '67-'68 bodies are the only ones I really would want to have if I could have another.

Keep it Pontiac and enjoy it just the way it is, you will be glad you did. :thumbsup:


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## New to GTO ? (Apr 16, 2020)

PontiacJim said:


> VIN numbers were not added until 1968. You can verify it to be a '67 block by looking by the distributor hole. The casting number for '67 400 blocks is 9786133 with the distributor hole taking out the "97." However, if it is a late 1967 block (as I recall cast after May), the 9786133 will be found on the block ledge behind the right head where the trans bolts up like all 1968 and up blocks - so this can help ID block casting time frame. Also, your block casting date codes will be found there - a letter and 3 digits. Assume heads have already been identified and the date codes?
> 
> The number you see is the Engine Unit Number and not related to the VIN.
> 
> Ton of info here at this website: Codes ?- First Generation Firebird (1967, 1968, 1969)


hey Jim,
This whole time I thought I had the wrong block!!! The YS was there but not the 97... thanks. So March 13 and my car production was June 11. That seem right to you?


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## Old Man Taylor (May 9, 2011)

It's a bigger difference than "typical", but not impossible. With the "normal" production flow the difference would be 3-4 weeks. However, strange things happen in production.


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## PontiacJim (Dec 29, 2012)

Old Man Taylor said:


> It's a bigger difference than "typical", but not impossible. With the "normal" production flow the difference would be 3-4 weeks. However, strange things happen in production.


X2, usually the casting dates are closer. Like the original post by
*Massrog, *the PHS documents will have the Engine Unit Number on the billing history which will confirm what engine code the car was manufactured with at the assembly line, and further confirm this by matching the factory EUN with yours - which will be the line of numbers above the 2-letter block code YS.


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## New to GTO ? (Apr 16, 2020)

The engine unit number matches my billing history. But my transmission only the PX seven matches. The other numbers are not the same on my belly history. Which is weird


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## New to GTO ? (Apr 16, 2020)

I currently have the block and heads and tranny all out of the car. Taking them to the machine shop. I had a good Pontiac 350 running in there currently with a 350 transmission. Temporarily until I get around to building the motor that came in it.


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## PontiacJim (Dec 29, 2012)

New to GTO ? said:


> The engine unit number matches my billing history. But my transmission only the PX seven matches. The other numbers are not the same on my belly history. Which is weird


The letter codes can be stamped wrong and even the billing engine letter codes can be mis-typed. I think I would rely more on the EUN than the engine letter code.

Not sure on the trans. Again, things are not always 100%, and/or people do re-stamp things. Might be a question for the PHS company people as they see these kinds of inconsistencies.


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## Hootchi (Apr 7, 2021)

This is really fascinating.(excuse my nerdy excitement) I just found my block number on my GTO today which is 687395 YS. It is not numbers matching to my VIN but am wondering what year it is, etc.


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## BearGFR (Aug 25, 2008)

Hootchi said:


> This is really fascinating.(excuse my nerdy excitement) I just found my block number on my GTO today which is 687395 YS. It is not numbers matching to my VIN but am wondering what year it is, etc.
> View attachment 142028


Sequence of steps to ID a Pontiac block:
1. You must start with the date code which is 4 digits, on top near the distributor hole. You have to know the date first because Pontiac on occasion used the same "two letter" code to mean different things in different years.
2. Block casting number, often found on the rear passenger side, cast into the block, just above where the transmission bolts up.
3. "Two letter" code (YS in your case).
4. Partial VIN stamp (I don't remember which year they started this - 67 or 68?) - passenger side, down low, alongside the timing cover.

Check here for some photos that show the locations:
How to identify your Pontiac engine


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## Hootchi (Apr 7, 2021)

BearGFR said:


> Sequence of steps to ID a Pontiac block:
> 1. You must start with the date code which is 4 digits, on top near the distributor hole. You have to know the date first because Pontiac on occasion used the same "two letter" code to mean different things in different years.
> 2. Block casting number, often found on the rear passenger side, cast into the block, just above where the transmission bolts up.
> 3. "Two letter" code (YS in your case).
> ...


Thank you for this.....Im not sure I can get to the ones that are up against the firewall but perhaps I can find the ones on the top by the distributor hole....Ill try that to start.


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