Oldsmobile 403 Technical Specs

OLDSMOBILE 403 TECHNICAL SPECS

The Oldsmobile produced 403 engine was available in the 77-79 Firebird and Trans Am models. It was a very low compression motor. Since the 403 engine was roughly the same displacement as the Pontiac 400, both the Oldsmobile engine and Pontiac engine bared teh 6.6L displacement logo, often creating confusion to people assuming it was a Pontiac engine. The easiest way to quickly notice an Oldsmobile motor is the oil filler tube in the front of the block above the timing cover, whereas a Pontiac motor has the oil filler on the valve cover. There are many other differences (valve covers, timing cover, exhaust manifold, etc), but that is the easiest way to ID the Oldsmobile engine.

 

403 OLDSMOBILE ENGINE SPECS

Engine Displacement :  403 CID (6.6L) Bore x Stroke :  4.351" × 3.385" Compression Ratio :  8.0:1 (low compression) HP rating (SAE) : 185 @ 3,600 rpm Torque rating (SAE) : 320 @ 2,200 rpm

 

403 OLDSMOBILE ENGINE INFO

403 engine blocks are cast with a "403" raised area between the freeze plugs denoting the displacement. 403 cylinder heads originally had 5-bolt valve cover holes, however, 5-bolt gaskets and valve covers are hard to find, and the more common 9-bolt covers and gaskets can be installed.  We typically install short bolts through the valve cover and use clips to hold them on the backside to fill the empty holes. Firebird/Trans Am applications used thick motor mount welded adapters on the block, and had Pontiac clam shell mounts on the frame.  It was very common to see cracks in those motor mount brackets.  They can be repaired by welding. Stock 403 exhaust manifolds used an open center port (cylinders 3 & 5, 4 & 6), and also used an exhaust crossover tube that went from the driver's side manifold to the passenger side manifold, and the passenger side manifold exited the exhaust.  This was not a performance method.  When converting to headers, be sure to order gaskets for headers, as most headers are split port.  Casting # :   554717 Combustion chamber :   83cc Intake valve size :   2.00" Exhaust valve size :   1.507"