# Need help decoding my engine block #



## mwinters (Oct 31, 2014)

Hey guys I have a 65 GTO with a motor that is not original to the car. I'm told its a 66 motor but I need to know for sure. 

The number in the front of the block on the passanger side is YF / 569945

The number on the back decking near the distributor is 68L8LL6

Any information would be great! How many years did they produce the YF block?


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## 05GTO (Oct 6, 2004)

The casting number is 9778789 and it was used for both 65 and 66, the letter code was also used for both years. The YF block was used in 65,66,67,68,69,73 and 74 and was not a GTO engine. You should have a date code next to the casting number that can give more information on the year. The head codes are located on the head at the center exhaust outlets.


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## mwinters (Oct 31, 2014)

05GTO said:


> The casting number is 9778789 and it was used for both 65 and 66, the letter code was also used for both years. The YF block was used in 65,66,67,68,69,73 and 74 and was not a GTO engine. You should have a date code next to the casting number that can give more information on the year. The head codes are located on the head at the center exhaust outlets.


Where did you come up with that casting number?


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## BearGFR (Aug 25, 2008)

The block casting number is going to be down low, behind the passenger side bank of cylinders, cast into the block near the edge where the transmission bolts up.

The date code (which is where we need to start) should be only 4 characters and located on the top center of the block near the distributor hole. The first character is alpha and indicates the month the block was cast. The next 2 are the day of that month, and the last is the year.

Helpful pictures here:
How to identify your Pontiac engine

Bear


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## rickm (Feb 8, 2012)

if its a '65-'66 YF, its a 325 hp. Bonneville motor automatic w a/c. 10.5 comp. 4bbl. I have one. with the slight up-grade of an 068 cam it runs real nice on Sunoco high test pump gas.


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## 05GTO (Oct 6, 2004)

mwinters said:


> Where did you come up with that casting number?


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## jmt455 (Mar 26, 2012)

05GTO said:


>


That's excellent; great catch, 05GTO.
I was looking at that part number and couldn't figure out WHAT it was. Never occurred to me it was the casting number upside-down.


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## 05GTO (Oct 6, 2004)

I've made the same mistake and spent hours searching for information on casting numbers.

:willy:


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