Small Block Functional Differences - 1964 - 1990


Small Block Functional Differences

307 Block Quality

There was a problem in 1987. I don't know if it is due to poor nickel quantity, but there was a cracking problem in the deck area. Engine rebuilders are aware of this and check the decks of 1987 307's very close.

Olds wasn't the only division to suffer in 1987. The small block Chevy cracked in the cam valley that year, and the 2.5 liter 4 cyl Pontiac suffered block and head cracking problems.

[ Thanks to Tony Waldner for this information ]

Solid / Windowed Main Bearing Webs

403's are usually the engine mentioned when windowed webs are discussed because there are rumors and some sightings of solid main web 403's. Solid main webs would mean a much stronger bottom end. As far as 403's go, some people doubt that a solid web engine was ever made. According to Mondello, 2500 solid web 403's were produced in 1977 and they were used in big Buick and Olds wagons. You can determine if you have a solid web by looking at the serial number.

All small block Olds engines produced after 1977 have windowed main webs, with exception of the diesel 350. Oldsmobile re-tooled the engine foundries in early 1977. This is the reason that you see so many 350 Chevy engines in 1977 Delta 88's. There was a shortage of 350 Olds engines, and the Cutlass line was selling like crazy, so those engines were reserved for that line.

403 Olds Solid Main Web Production

2500 produced
Block Casting Numbers: 557265-4A, 553990-4A, 554990-4A
Blocks with these casting numbers were used in certain 1977 Buick Station Wagons built in 1976, the Pontiac Bonneville with tow package, the 1979 Pontiac Trans Am with tow package (w/block casting #554990-4A), and in 1977 Olds 98's. Block casting number is found behind the timing cover between the oil fill tube and the oil sending unit. Might also be found in 1977 Toronados.

All "4A" blocks don't necessary have solid main webs. #554990 has been found to have open webs. 1977 models built early in the model year, fall of 1976, are likely to have solid main webs.

Source: Mondello Olds V-8 Engine Technical Reference Manual

[ Thanks to Michael R. Hall, Chris B. Witt, Tony Waldner, Mark Prince for this information ]