The 1991-1997 V8 Ford Thunderbirds came with two different engines depending on the model year. The early 1991-1993 models came with 5.0L V8s. After 1993, the engine changed to a Modular 4.6L V8, which was similar to the 1996 Mustang GTs. As you can see from the below, the performance changed slightly between each engine and Modular design.
| 4.6L Specs | 5.0L Specs | |
| Engine | 90 degree V-8 | 90 degree V-8 |
| Displacement | 281 cubic inches | 302 cubic inches or 4,942 cubic cm |
| Valve train | 2 Overhead camshafts driven via chains | One in block camshaft driven via chain |
| Valves | 16, 2 per cylinder | 16, 2 per cylinder |
| Cylinder heads | Cast-aluminium | Cast-iron |
| Cylinder block | Cast-iron with a 4-bolt main | Cast-iron with 2-bolt main |
| Bore X Stroke | 3.552 x 3.543 inches | 4.00 x 3.00 inches |
| Compression ratio | 9.0:1 | 9.0:1 |
| '94-'95 HP & TQ SAE-net | 205 hp @ 4,500 rpm 265 lbs.-ft. of torque @ 3,200 rpm |
200 hp @ 4,000 rpm 275 lbs.-ft. of torque @ 3,000 rpm |
| '96-'97 HP & TQ SAE-net | 205 hp @ 4,250 rpm 280 lbs.-ft. of torque @ 3,000 rpm |
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| '99 Mustang HP & TQ SAE-net | 260 hp @ 5,250 rpm 302 lbs.-ft. of torque @ 4,000 rpm |
"> Which engine is best is up for debate. The early 5.0L engines have a large aftermarket due to its Mustang roots. The 1994-1995 Modular is based off of the 1991 Lincoln Town Car design and is very durable. The only issue with the early Modulars is oil burning due to bad valve stems. The 1996-1997 models suffer from problems with the intake manifold coolant leaking, but they make a P.I swap easier then the early version.