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The Iron Duke Resource Site



Welcome to my newly redesigned Fiero 2M4 resource site.  The original site recorded over 12000 visits,  hopefully this one will also prove as useful.
Ira Crummey

Variations of the 2.5L ohv GM four cylinder engine.

There are several variations on the 2.5L engine used in GM models.  Before using a non-Fiero block as an engine replacement check out the following list.

The Information in this table is also courtesy of Gary Ohst.  The comment which prompted this response on the Fiero Mailing list was from Sketch and an excerpt of his letter is reprinted below:
"...I recall a URL posted on one of the lists quite some time ago that was a technical article about the Duke, on a site oriented towards professional
mechanics.  They mentioned one problem with the stock FWD blocks was that two of the cylinders at one end were actually closer together. Instead of having round cylinder liners, they cut a slice off of one edge on two of the cylinders, and moved them closer together to make the engine shorter...."

Stay away from the oddball FWD only VIN U motor, too many parts are different compared to all other 2.5 motors.  It was used only in FWD N-cars, Grand Am, Calais, etc.  Crank thrust bearing and cylinder head bolt pattern are a few (see below).  The VIN R (Fiero included) motors were used in both larger FWD cars (X and A body cars) and RWD applications with no special mods.

The S-10 truck block is good because it has solid main webs like the SD block. It is cast from average grade iron though, where as, the SD block uses 40,000 psi high nickel iron.  The SD blocks come drilled for a starter mount on both sides.

The Vin E 2.5 liter truck motor was used in both Astro/Safari vans and the S-10/S-15 trucks. I think the later model 1991+ VIN A was only used in the pick-up trucks. The pick-up trucks have the starter on the right and the vans have it on the left (fiero side). Starter location can be changed
Here are some general VIN notes regarding the various 2.5 liter motors:

Vin V 1977-1980 Carb  non cross-flow head (intake & exhaust manifold on same side)
Vin 1 1978-1979 Carb  non cross-flow head
Vin 9 1979      Carb  non cross-flow head
Vin F 1980-1983 Carb  export only
Vin 5 1982-1983 Carb  cross-flow heads from 1982 on
Vin 2 1982-1986 TBI  Thrust brg length 1.009, Head bolt spacing 3.75
Vin R 1982-1992 TBI  FWD/RWD/Fiero    Thrust brg length 1.009, Head bolt spacing 3.75
Vin U 1985-1991 TBI  N-car FWD Only   Thrust brg length 0.940, Head bolt spacing 3.67
Vin E 1985-1991 TBI  S-10, Astro Van  Thrust brg length 1.009, Head bolt spacing 3.75
Vin A 1991-1993 TBI  S-10 Thrust brg length 1.009, Head bolt spacing 3.75

The VIN E and A truck motors were also used in postal vehicles.  That's right, the mailman has a better block than you do ;)

If anyone can correct or add to the the above info, please do.  Email  Ira