Similarities Other GM Engines - 1964 - 1990


Similarities: Other GM Engines

A Olds 350 is not a Buick 350 is not a Pontiac 350 is not a Chevy 350, is not a Cadillac 350, small and big block! This applies to Olds small block and big block engines. The only things in common with other GM division engines are the distributor cap, rotor, carb bolt pattern, and the transmission bolt pattern. Buick, Cadillac, Olds and Pontiac are the same, with five bolts. Chevy is different, with four bolts.

Chevy's are bigger and heavier than comparable CID Olds engines since they used very little Nickel in the cast iron. Nickel is a expensive strengthening agent for cast iron. Low quality iron requires mass in order to make it stronger, which is why you will see the physical weight and size difference.

I hope you don't think that 4 bolt mains were put in Chevy engines so that they would be "Ultra-Strong" for the performance enthusiast. This is simply not true, they are there because the iron requires strength to keep the cap in place and 2 bolts in mush is not as good as 4 bolts in mush.

Oldsmobile blocks aren't made of mush, rather, they are made of high quality Cast Iron with plenty of Nickel to make it strong. Olds big block engines were cast with extremely high nickel content until mid 1970. You can easily spot the difference in the shape of the "F" near the oil sending unit. Look at any 1968 1969 and early 1970 block and the F will be different in shape than any late 1970 to 1974 block. In 1975 the nickel content was lowered even more. These engines will have no mounting hole for a clutch swivel rod ball, either.

As the weight of the engines go (stock engine weights):
Model Size Weight(lbs) Notes
Buick 455 600-640 (the later may be with accessories)
Cadillac 500 750
Chevy 350 535
Chevy 454 685
Olds 350 560
Olds 425 660 (flywheel, exhaust manifolds, cross over pipe, starter, water pump, alternater, carb, 5 quarts oil, distributer, etc.)
Olds 455 620
Pontiac 389 650 (a 455 should be the same weight)

And internal comparisons on bore, stoke and bearing sizes:
Maker Size Bore Stroke Mains Rods
Olds 455 4.126 4.25 3.00 2.50
Pontiac 455 4.152 4.21 3.00 2.25
Buick 455 4.312 3.90 3.25 2.25
Olds 350 4.057 3.385 2.50 2.125
Pontiac 350 3.876 3.75 3.00 2.25
Buick 350 3.80 3.85 3.00 2.00
Olds 400Early 4.00 3.975 3.00 2.50
Olds 400Late 3.87 4.25 3.00 2.50
Olds 403 4.351 3.385 2.50 2.125
Pontiac 400 4.121 3.75 3.00 2.25
Buick 400 ??? ??? 3.25 2.25

The Chevy 307 from the late 60s to early 70s is a real small block Chevy engine and not to be confused with the 307 Olds from the 80s, which is a real Oldsmobile engine and common to other small block Olds motors (260-307-330-350-403). The two are totally different in bore, stroke, bore spacing, block casting, head casting, etc. Nothing is interchangeable. Pontiac had a 301 engine in the late 70s-early 80s, which is a Pontiac engine, and somewhat common to other Pontiac engines (326-350-389-400-428).

GM confuses people by first having each division build totally different engines with the same displacement (at least, after rounding off), such as the four different 350s, in the 60s, then mixing engines and divisions (such as the 305 Chevy used in Oldsmobiles, or the 403 Olds used in Buicks) when they started to pare down this overlap in the mid-70s.

The real simple way to tell these late model GM engines apart is the following:

Olds (big and small block):

  • Separate oil filler tube on front of block above water pump.
  • Rear mounted distributor.
  • Five bolts hold each exhaust manifold on to head: four in a line and the fifth one above and centered between the two middle exhaust ports.
  • Starter on driver's side.
  • Oil filter on passenger's side.
  • Six bolts holding transmission bellhousing to block.
  • Flat plate timing chain cover with open-back water pump which seals to the plate.
  • Valve covers shaped like trapezoid with rounded sides (top rail shorter than bottom rail) and held on with ten bolts (on some later engines, only five are used but all ten locations are on the cover).

Chevy (small block):

  • Oil filler in valve cover.
  • Rear mounted distributor.
  • Rectangular valve covers with four bolts each (later LT-1 motors have valve cover bolts passing through center of valve cover instead of the outside edges).
  • Starter on passenger's side.
  • Oil filter on driver's side.
  • Five bolts holding transmission bellhousing to block, including one at the top center of the bellhousing.
  • Stamped, raised timing chain cover.
  • Water pump straddles the timing chain cover and has two ports which attach directly to the heads.

Buick (big and small block):

  • Oil filler in valve cover.
  • Front-mounted distributor (only GM V-8 other than Caddy).
  • Four separate exhaust ports with two bolts on each.
  • Cast aluminum front cover with external oil pump (there is a separate plate on the bottom of the front cover which can be removed to expose the oil pump gears).
  • Water pump bolts into front cover.
  • Six bolts on bellhousing.
  • Thermostat housing faces forward.
  • 4 bolts for valve covers.

Pontiac (big and small block):

  • Oil filler in valve cover.
  • Rear-mounted distributor.
  • Intake manifold runners separate from valley cover. Careful, this is similar to the 1964 and earlier first generation Olds V-8, and the aluminum 215 Buick. But those should be easy to identify.
  • Six bolts in bellhousing.
  • Valve covers have rounded ends and are held on with four bolts.
  • 6 bolts for the exhaust manifolds.
  • Used the same block for all engines, from the 326 through the 455. The 301 is a lower-deck version of the same block.
[ Thanks to Fernando Proietto, Michael R. Hall, Tony Waldner, Joe Padavano, Doug Ahern, Bob Barry, Daren for this information ]