On a cold, goopy SoCal winter day, a couple of members of the CC crew were on a field trip to the Blinn Avenue Pick Your Part in Wilmington, California. About halfway through the Ford section, we were surprised to see an all-aluminum V-8 engine discarded upside down on a slab. What was it doing there? Why did someone throw away something with factory overhead cams and cross-bolted main caps? Had it been half-price Tuesday, we would have bought the thing just for the sake of saving a chunk of American aluminum, but we wouldn't know what to do with it. Instead, we became interested in the pariah of Mustang engines, the 281-inch (4.6L) mod motor. Can it be swapped into a muscle car-era Mustang? Should it be? Should we just buy a '96-and-later 4.6 Mustang instead? We have looked for the answers to these questions so you can decide for yourself.
Don't be fooled by the early...
Don't be fooled by the early Crown Victoria and its easily plucked 4.6L. It will have the non-PI heads and is virtually worthless when there is likely a PI version parked right next to it.
4.6 Two-Valve
To be brief, the 4.6L is called the modular motor because it can be easily changed from V-6 to V-8 to V-10 configurations. There are iron-block 4.6L engines with two-, three-, or four-valve heads, iron or aluminum blocks.
While the two-valve started life in 1991 powering big cars like Crown Victoria then Thunderbird it's performance potential and broad appeal started with Mustang. In late 1994 Ford introduced the SN-95 Mustang, a new chassis replaced the aging but cool Fox 5.0 platform and a modern engine was promised to go with it. The '95 Mustang retained the original 5.0L engine, and the '96 was the first to feature a two-valve version of the 4.6L V-8 with an iron block. The engine featured factory aluminum heads and overhead cams that promised to eliminate the theoretical high-rpm problems presented by pushrod valvetrains.
The '96 Mustang GT had a 225hp rating (although most references say 210 to 215 was the actual output) and changed little until the introduction of the Power Improved (PI) cylinder head in 1999. The PI engine was rated at 260 hp because of a new combustion chamber design, intake runner shape, and cam timing. The PI iron-block two-valve 4.6L can be found in the '96 to '04 Mustang GT and the '01 to present Crown Victoria and Grand Marquis.
Aside from identifying the...
Aside from identifying the year of the vehicle, the quick way to spot a non-PI 4.6L engine is the intake port. Note the shape of the intake runner is circular compared with the rectangular PI head.
4.6 Three-Valve
In 2005, the Mustang GT got a new 4.6L engine with a three-valve head. The additional intake valve and improved cylinder head flow numbers upped the factory rating for the Mustang GT to 300 hp. Because the 4.6L three-valve is a Mustang application, it already has plenty of aftermarket support, and because of extra valve area, it is perfect for superchargers. In addition to centrifugal kits from Paxton and Vortech that advertise up to 500 hp, Ford Racing offers an Eaton supercharger kit that adds 100 hp and a big-boost kit that adds 250 hp that is 50-states legal and in some cases has a warranty.
4.6 Four-Valve
If you had a little more coin in 1996, you could buy an SVT Cobra instead of the Mustang GT. The Cobra was equipped with the aluminum-block 4.6L with a dimensionally larger four-valve Swirl Port head and a rating of 305 hp. These engines used Intake Manifold Runner Control (IMRC) that improves performance when a second runner opens in the plenum. The engines are referred to as having B-port heads and were available in '96 to '98 Cobras. The 4.6L four-valve engine continued in the '99 to '01 Cobra without the IMRC and with the addition of the redesigned Tumble Port heads also referred to as C-port heads. This engine also eliminated the return fuel system and added coil-on-plug ignition. The C-port Cobra engine was rated at 320 hp.
Likely the ultimate 4.6L four-valve appeared in the '03 to '04 Mustang Cobra with an Eaton supercharger and a rating of 390 hp. The real potential is revealed with a freer flowing exhaust and added boost via pulley change or supercharger swap (it's not really headers; it's more after the manifold and the boost that gets in) that push the engine to more than 500 hp at the crank.