Cut and pasted from somewhere on the web:
1979: Horsepower was 140. Engine was junk. Leak prone 2 piece rear main seal. 8.4:1 compression cast pistons, economy cam, 369cfm two barrel carb, mechanical fuel delivery system, junk heads, cast
iron exhaust manifolds, single 2 inch exhaust.
1980-1981: No 5.0 instead it was a 4.2 V8 totally junk with no performance potential.
1982 5.0 H.O: 157 horsepower, 8.4:1 compression cast pistons, a roller timing chain, 369 cfm motorcraft 2 barrel carb, flat tappet marine camshaft, internal balance changed to utilize 50 oz. imbalance. components and a thincast 302 block. Things improved for this year
but the engine still had little performance potential. Heads had tiny ports and small valves, pistons are cast and low compression,
block is pretty weak. Last engine to use the 2 piece rear main seal.
1983 5.0 H.O: 175 horsepower, basically same as 1982 with some minor changes. Heads, camshaft, exhaust manifolds and pistons were all
carryovers from 1982. Added 600 cfm Holley 4 barrel and the crankshaft and block were altered to use a one piece main seal. Still very limited performance potential due to pistons, cam, heads
and weak block.
1984 5.0 H.O: Engine was exactly the same as 1983. First year for fuel injection. All AOD mustangs got the Low pressure Central Fuel
Injection equipped with two 52-lbs-hr injectors. This system has absolutely no performance potential.
1985 5.0 H.O: 210 horsepower. First hydraulic roller tappet camshaft, forged 8.4:1 compression pistons, tubular exhaust manifolds
with 2 1/2 exits, improved heads. Roller cam provided improved breathing along with tubular dual exhaust. Induction system used an
improved Holley carb while the AOD mustangs still had the CFI fuel injection. The carb cars could be modified the usual ways while the
AOD cars still offered no performance potential. Performance still limited on carb cars due to weak roller cam block, poor heads, low compression.
1986 5.0 H.O: 200 horsepower but increased torque to 285 lbs-ft. Stronger block, compression increased to 9.2, heads were a little
better with improved swirl and rate of burn. First year for multi- port fuel injection (Speed Density). Came with 19 lbs-hr. injectors.
Roller cam was carryover from 1985. Tubular exhaust manifolds were changed to eliminate the cold start exhaust control valve and the
outlet size changed to 2 1/4". Still lacks performance potential due
to lack of valve eyebrows in the pistons, high swirl combustion chambers are useless for performance so heads are junk, intake
manifold has tiny ports and a 58 mm throttle body. The Speed Density fuel injection has trouble handling performance parts. Can buy
a conversion kit to convert to mass air system.
1987 - 1988 5.0 H.O: In 1987 Ford switched to the truck head with larger ports and valves, 9.0 compression forged pistons with valve
eyebrows, larger runner intake and 60 mm throttle body. Still used Speed Density though. Camshaft, exhaust manifolds and block were
carried over from 1986. Offered good performance potential when converted to mass air.
1989 - 1992 5.0 H.O.: 225 horsepower. This series of engines offer the greatest
performance potential of all the 5.0 H.O engines. Block, heads, intake and exhaust manifolds are unchanged from 1987. Introduction
of the 55 mm Mass Air fuel injection system allows use of radical camshafts. These engines are the best choice for performance.
1993 5.0 H.O: Basically indentical to 1989 - 1992 except for one important change. Went to cheaper cast hypereutectic aluminum pistons
instead of using the previous expensive forged pistons. Good pistons but use of a cast piston hinders high performance. Turbo, super-
charging, or nitrous are pretty much out of the question. These cast pistons can only handle modest power gains before they die.
1993 5.0 Cobra: 235 horsepower. Cast iron GT-40 heads, SSC type exhaust manifolds, cast aluminum GT-40 style intake, 65 mm throttle
body, 24 lbs-hr injectors, 70mm mass air meter, shorter duration, higher lift camshaft, 1.72 rockers and a specially programmed EEC-IV
computer. However, it also contains those junk pistons noted above.
If you are shopping around for a Mustang with the intent of modifing it, your best bet is to stick with a 1989 to 1992 car.