Pontiac 400 Engine Identification

Written by rob wagner
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The Pontiac 400-cubic-inch V8 was the largest engine to power the first generation (1967 to 1969) Pontiac Firebirds and GTOs. Larger V-8s followed for the 1970 to 1981 Pontiacs. The automaker produced the 400, which was essentially a bored-out 389 engine, from 1967 to 1979. Identification of the 400 is relatively easy, whether the engine is mounted in the car or on an engine stand, due to its distinct physical characteristics and casting codes.

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Background

The 400 garnered a following among muscle car enthusiasts for its high output of 335 horsepower and 441 foot-pounds of torque. The High Output 400 developed 360 horsepower and 438 foot-pounds of torque with the aid of a four-barrel carburettor. The Ram Air version developed 360 horsepower. The engine featured a 4.125-inch bore and a 3.750-inch stroke. The 400 is easy to identify, since it carried some of the 389's physical attributes.

Appearance

The 400 features three freeze plugs on each side of the block. Pontiac engineers slightly altered the angle and enlarged the valves to 2.11 inches for intake and 1.77 inches for exhaust for better breathing on the four-barrel carburettor models, and to 1.96-inch intake and 1.66-inch for exhaust on the two-barrel carburettor versions. In mid-1967, Pontiac moved the block casting numbers of the 400 V8 to the rear of the block behind the No. 8 cylinder from the distributor pad.

Casting Numbers

The casting number for the 1967 400 V8 block is 9786133. For 1968, it's 9790071. The 1968 400 Ram Air casting number is 9792506. For the 1969 model year, the standard 400 had the number 9790071, while the Ram Air IV version was stamped with 9792506. The extremely rare Ram Air V 400s have 9792968 and 545887 stamped on the engine blocks. Model year 1970 through 1979 have similar numbers stamped in the same location, at the rear of the block.

Date Code

The driver's side back portion of the block features a stamped letter for the month of manufacture, followed by digits that denote the day and year. For example, an "A249" identifies the block as manufactured on January 24, 1969. "A" identifies the month of January, "24" identifies the day and "9" the year. Following the four-digit code is a second two-letter code. This code identifies the vehicle. An "XM" for example, identifies the 400 V8 as belonging to a 1967 Pontiac GTO; a "YI" identifies the 400 as a Ram Air version.

Other Identifiers

The 1969 and older 400 V-8s feature two mounting holes/pads for the motor mounts. Post-1969 models have three or five mounting holes/pads. Cubic inch displacement codes didn't appear on the 400 until 1971. A stamped "400" appears on the side of the block and "00" can be seen in the lifter valley. Pontiac heads, intake and exhaust manifolds have stamped casting codes that identify the valve size and help determine whether the manifolds are original to the engine by matching the casting codes to the two-letter date codes.

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