Muscle Mustangs & Fast FordsHow To Engine
The Four-Valve Swap Power Struggle Upgrade
When You Need 9-Second Muscle And Your Two-Valve Engine Can't Hack It, Swap It Out For A Four-Valve.
These advantages really add up in horsepower production. Papitto was convinced that the sleeved block caused most of the head gasket failures, but he was also very emphatic that the Two-Valve arrangement could still cause detonation and additional head gasket problems at the power level the car had attained. That was the final nail in the Two-Valve motor's coffin. Head gaskets were not going to be a routine maintenance item on the new mill.
There is, of course, a downside to the Four-Valve decision, too; namely, the funding to replace a significant number of components that are required for the conversion. Our subject vehicle incurred more costs than a basic Four-Valve-to-Two-Valve swap in that many of its engine components, the Vortech supercharger system in particular, are specific to the Two-Valve Bullitt Mustang. This required obtaining even more parts that are specific to the Four-Valve Mach 1 or Cobra modular engines.
Since we have high expectations (i.e., high power output and reliability) for this build, we didn't scrimp on the short-block. Al Papitto worked his magic on the engine to accomplish our goals. He started with a standard-stroke crank and a 0.030-inch overbore on the cylinders because he believes the stroker combinations for modular motors present too many compromises, including less than desirable rod ratios and ring configurations.
With the decision to go with a standard stroke, we considered our block options. It would have been easy and cheap to go with a new steel block, but aluminum offers an approximate 70-pound weight reduction directly over the front wheels. That being said, we called around and were able to acquire a Teksid aluminum block from Darrin Burch of BC Automotive.
We hoped to reuse the rotating assembly from the Two-Valve engine, but Papitto noticed some feathering of the balancer keyway. Since it was marginal, we decided to replace it with a new Kellogg forged-steel unit. The Oliver billet connecting rods were reused, but the pistons are new pieces from CP Pistons. Given the combustion chamber in the heads and the 9cc dish in the pistons, the compression worked out to a rather high (for a supercharged application) 9.5:1. This was to maintain good throttle response.
The CP pistons were fitted with a Mahle ring package, and the 4.6L block received a Boss 330 Racing-spec Melling oil pump. Considered by many to be a weak point in these motors developing high rpm, Papitto worked with Melling to develop a reliable oil-pump design.
The pivotal piece of hardware in this upgrade is, of course, the cylinder heads. There have actually been several different editions of quad-valve heads produced for the modular motors. The first was the "B" casting cylinder head that was attached to the Lincoln Mark VIIIs and SVT Cobras until 1998. In 1999, Ford released the "C" casting Tumble Port head, which lasted until 2001. Ford Racing Performance Parts released the FR500 four-valve head in 2002, which featured better low and mid-lift flow numbers than the Tumble Port design. The FR500 heads, with some slight updates, eventually became the U231 casting used on the '03-'04 SVT Terminator Cobras.