[FASTASSBIRD]

Originally Posted by caddor38

Thanks for providing the info on the Vin. I thought the number was high with 7 digits, so can i assume this was the 4,555th car built in the 3,000 series in Pontiac Michigan. However, the motor began as a HO block since it was given a 4 bolt main. However since it was probably detuned to the 8.2 compression 325HP version folks are saying its non-HO and there are many sites calling the detuned vs an HO motor and some sites dont. My contention is that once they created the block in 1970, with a 4 bolt main and stamped it 484677, the block was then a 455HO according to my info.

The big problem you face is yes the block was CAST in 1970. Unfortunate the cast date is in September of 1970. That means the block was cast AT LEAST 2 months into 1971 production. Casting and cars don’t run on the same Jan-Dec calendar we do. They run run on an august -July calendar with new models being available for purchase in sept. Meaning parts have to be cast as early as July for them to be able to produce cars for sale on sept 1. Your block being CAST after sept would then have to go through ALL the steps and processes to be ready to insert on an assembly line. In a perfect world with shipping manifesting inventorying transport to the line etc I’d say it would take at least 2 weeks to be ready to be put into a car. Now we are Oct in a perfect world. Maybe even Nov of 70. Well into the 1971 model year. My guess is like the WT motors of the 70 model year (also cast in the 69 year up til Dec) a few had 4 bolt caps added for god knows what reason. These things happen. However the YC code is the application code and idc if it has 6 bolt mains it’ll always be looked at as the base 455. I think your big hang up is it being a “70” block it isn’t it is a 71 which is why I took the time to explain the dating structure. Also the vin confirms that. I do think the mains were factory installed probably but not with the intent of it being a “HO” motor or “detuned” motor. Other then the caps the blocks are the same.

[caddor38]

Originally Posted by FASTASSBIRD

The big problem you face is yes the block was CAST in 1970. Unfortunate the cast date is in September of 1970. That means the block was cast AT LEAST 2 months into 1971 production. Casting and cars don’t run on the same Jan-Dec calendar we do. They run run on an august -July calendar with new models being available for purchase in sept. Meaning parts have to be cast as early as July for them to be able to produce cars for sale on sept 1. Your block being CAST after sept would then have to go through ALL the steps and processes to be ready to insert on an assembly line. In a perfect world with shipping manifesting inventorying transport to the line etc I’d say it would take at least 2 weeks to be ready to be put into a car. Now we are Oct in a perfect world. Maybe even Nov of 70. Well into the 1971 model year. My guess is like the WT motors of the 70 model year (also cast in the 69 year up til Dec) a few had 4 bolt caps added for god knows what reason. These things happen. However the YC code is the application code and idc if it has 6 bolt mains it’ll always be looked at as the base 455. I think your big hang up is it being a “70” block it isn’t it is a 71 which is why I took the time to explain the dating structure. Also the vin confirms that. I do think the mains were factory installed probably but not with the intent of it being a “HO” motor or “detuned” motor. Other then the caps the blocks are the same.

Yep, I concur and understand what your saying, yet there are a couple of ways to look at this. This particular YC motor with the 483677 stamp was made from July thru September and the later YC motors were given the 485428 stamp. The pontiac sites are calling the 483677 motors HO and the 485428 stamp non-HO motors. So, like a contract is written I am taking the verbage of what is written, however i do understand that folks may not want a motor that was installed in a vega or pinto in their GTO. However I think this motor could be considered a year correct HO motor as defined by multiple service bulletins abd pontiac sites.