Where is the date code casting numbers on a 70 olds 350 engine. The engine in our Rallye 350 was replaced shortly after it was sold new & since it is a 4 speed rallye & has a 253 carb it could be a QB engine & knowing the manufacture date would help identify it .

 

The block casting date is by the distributor hole. What's the build date on the cowl tag?

 

Car build date don’t apply because original owner told me Oldsmobile replaced the motor a few months after the car was new due to a piston failure .

 

In your example is 175 meaning the 175 th day of the year ? How do you determine the year ?

 

If the motor was replaced, how do you know what it is without checking the cam? The main difference between the QB and lesser 350s is the cam profile. Noting on the date code will tell you that.

From the 1970 Engine Assembly Manual:

QB engines got the 393859 cam. 286/286 deg duration, 58 deg overlap, and 0.472/0.472 lift.
Lesser 350s (including the service replacement long block) got the 400084 cam. 250/264 deg duration, 36 deg overlap, 0.400/0.400 lift.

Unless someone specifically replaced the cam in that service replacement long block with the correct one for a QB motor, it's not. Apparently the original motor was a QB, which is why you have the '253 carb. They simply transferred that from the old motor.

 

Makes sense to me now.

 

The year is the second character of the VIN derivative stamp. Contrary to what you may read on the interwebs, the mold number is not directly traceable to a year. The three digit date code is the day of the year. For a 1970 production car, blocks would have been cast from about July 1969 through June 1970. Service replacement motors came from that model year's production. Numbers 181-lower are likely 1970 calendar year (June 30 was the 181st day of 1970). Casting might have gone into early July, so possibly as high as 200, 210. Anything higher than that is almost certainly a 1969 casting date.

 

It never ceases to amaze me how much significance is attached to functionally equivalent series tracking numbers.