Big Block Unit Numbers :: 1965 - 1976


Big Block Unit Numbers

Pre 1968 engines also had an engine unit number stamped on to the machined pad at the front of the RH head. I believe that the Toronado 425's started with a T rather than a V.

V 001001 1965   400 442's
V 100001 1966   400 442's
V 200001 G 1967 400 4V 442's, including W-30
V 200002 1967   400 2V 442's, [etc.?] Turnpike Cruiser

1968 and up engines had an engine unit number stamped into the oil fill tube, the first digit of which will match the last digit of the car's year: 9012345 would be a 1969 engine [or 1979 small block]. Since this part is easily removed or replaced, use it for an indication, not a standard. No point in mentioning the oil fill tube decal with a 2-letter engine ID code, which is 99.99% of the time long gone, and easily replaced or faked anyway.

Also starting in 1968, the VIN derivative of the engine's original car was stamped onto the vertical machined pad on the left side of the block, at the front, just under the head- block interface. It might look like "38M203456", where:

3= Oldsmobile, GM's 3rd division [1=Chevy, 2=Pontiac, 4=Buick, etc.]
8= year of issue last digit, like on oil fill tube [8=1968, 0=1970...]
M= build plant [1, E, G, M, R, or Z; see below], and 203456= the last 6 digits of the original car's VIN.

Build plant info was also used in the car's VIN plate [1 character] and body tag [up to 3 letters]. Some build plants were: 1 or OS= Oshawa, Canada, eh?; B or BA= Baltimore, MD; E or BL= Linden, NJ; G or FRA= Framingham, MA; K or KC= Kansas City, MO; LA, LAN, or M= Lansing, MI; R= Arlington, TX; BF or Z= Fremont, CA;

That'll help ID the block year in case the heads are not original.

For the purists: on the back of the block, near the distributor, is a 1 to 3 digit cast number, digits about 3/8", which is the Julian day of the year on which the block was cast [1 to 365]. It will generally match the Julian Day code cast into the heads, crankshaft, water pump, thermostat outlet, etc. within a few [up to 20-30] days, and precede the car's date of build by up to 30-40 days.

[ Thanks to Chris Witt for this information ]