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Supercharged 4.6L Two-Valve Motor - 2V Or Not 2V
Supercharging the 4.6L Two-Valve motor to keep up with the Joneses
With the introduction of the new 5.0L, Four-Valve Coyote motor, the original Two-Valve has taken yet another step back in terms of popularity. The Three- and Four-Valve variants get all the publicity since they offer greater potential, but does that mean we should summarily dismiss the Two-Valve? Not hardly, as the Two-Valve remains popular due to its combination of availability and affordability.
Though not technically a series, we recently ran a pair of articles on the 4.6L Two-Valve motor in the last few issues. The first article dealt with adding bolt-ons to a wrecking-yard motor. Replacing the non-PI heads, cams, and induction with a pair of ported heads from Total Engine Airflow, a set of Comp cams, and the PI induction system increased output from 260 hp and 341 lb-ft of torque to 390 hp and 384 lb-ft. Obviously, the 4.6L GT motors respond well to bolt-ons, as we were able to improve the output by 130 hp by simply replacing the heads, cams and induction.
We followed this by building a dedicated 5.0L Two-Valve stroker using the only aftermarket heads in the industry. The 5.0L stroker combined additional displacement with wilder cams, elevated compression, and high-flow heads and intake from Trick Flow Specialties to create an impressive all-motor monster. So equipped, the 5.0L Two-Valve produced peak numbers of 463 hp and 430 lb-ft of torque. Adding a little shot of nitrous pushed the peak numbers to 604 hp and 588 lb-ft. Numbers like these bring serious respect on the street, as they thrust a Mustang into the 10s with sufficient traction.
Happy as we were with the results of both the bolt-ons and all-motor/ nitrous combinations, we couldn’t help but notice that our Two-Valve had yet to be subjected to boost. Knowing every motor deserves positive pressure, we decided our next move would be forced induction.
Before moving to our boost builder, we had a decision to make. Having built a pair of Two-Valve motors already, we had to choose one to supercharge. In one corner was the wrecking-yard short-block equipped with ported heads, cams, and PI induction; in the other was the high-compression 5.0L stroker. Unfortunately, neither was ideal for boost, as the stock internals on the 4.6L (bolt-on) motor would not withstand our intended power levels. The 5.0L stroker was sporting forged internals, but the high static compression (over 11.0:1) made it less than ideal for anything but an all-out race-fuel effort.
In the end, we decided to upgrade the short-block on the wrecking-yard motor with forged internals. We wouldn’t be using the very desirable heads and induction system from Trick Flow Specialties, but we liked the idea of having the 5.0L stoker ready to run.
The ’97 4.6L Two-Valve (non-PI) motor was disassembled and sent out for machining and a new set of internals. We ditched the stock cast (six-bolt) crank, rods and pistons and installed a complete rotating assembly from Coast High Performance. On this application, we decided to stick with the stock displacement other than a 0.020-inch overbore. Coast High Performance supplied forged pistons from Probe Racing, each featuring a 10cc dish. When combined with the 45cc combustion chambers on the TEA-ported PI heads, the result was a static compression right near 10.0:1. Down slightly from either the previous PI/non-PI bolt-on motor or the 5.0L stroker, the 10.0:1 was a perfect compromise between the ultra low compression often run on forced-induction motors and the high-compression, all-motor combos.
Running 10.0:1 instead of 9.0:1 or even 8.5:1 will make the motor much more responsive off boost, to say nothing of improving both fuel mileage and overall power. The forged pistons were combined with forged (stock length) connecting rods and an eight-bolt, forged-steel Cobra crankshaft. Naturally the eight-bolt crank required a matching flywheel or flexplate, but we had that at our disposal for dyno use. After installing the forged rotating assembly into the freshly machined block (by L&R Engines), our short-block was officially boost-ready.