2.5L L4 Engine Info

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"Are there casting marks or numbers which would verify that a block in a Fiero actually started out in a Fiero?"


1984   2.5   Z3J, Z3L, Z5L, Z5M, Z3K, Z5C
1985   2.5   ACM, ABY, ADJ, ADK, AAF, ACC
1986   2.5   B4C, B4F, BBY, BBZ
1987   2.5   WUA, WUB
1988   2.5   XHM, XHN

Engine number location: vertical pad on front of block, below cylinder head above waterpump.

All the 2.5 L4 (Iron Duke, Tech 4) engines used in GM cars are the same (and all are made by Pontiac) except for running changes made to the engine.

They have been used starting in 1977 in Astras, Sunbirds, Monza, Skyhawk and Skylarks. Since then they have been used in almost every GM FWD along with Camaros, Firebirds, S-10 trucks and Blazers and even Jeep Cherokees.

1977        88 horsepower     2 bbl carb     8.0:1 comp. ratio
1978        88 hp             2 bbl carb     8.0:1
1979-81     90 hp             2 bbl carb     8.2:1
1982-83     90 hp             TBI            8.2
1983-87     92 hp             TBI            9.0:1
1988        98 hp             TBI            9.0:1

Early 2.5s did not have a "crossflow" head. They were added in 1980.

In 1984 a new head was used that included "Swirl-Port" chambers and increased compression ratios from 8.2:1 to 9.0:1

In 1985 roller valve lifters, a new crankshaft and better bearings were added.

1987 a serpentine belt system and crank-triggered ignition (DIS) was added.

1988 a balance shaft system was added to smooth out the engine. New pistons, connecting rods and crankshaft were added along with the in-the-pan oil pump and filter. Results, 6 horsepower.

From: Scott Backer

Pontiac also had a fairly successful racing program using an engine called the Super Duty 4, which was based on this engine.

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