Thump, thump went the exhaust pipes as the sizzling Three-Valve engine idled with intimidation. Fellow S197 owners looked on with envy as Justin Burcham of JPC Racing warmed up a customer's '06 Mustang GT, which had just been the recipient of a pair of Comp Cams 3V bumpsticks. Each rap of the throttle was like an orchestra hitting a high note at the request of the conductor. This ponycar sounded mean, and surprisingly, the engine is largely stock save for the usual repertoire of bolt-ons and the aforementioned camshafts. As you read on, the performance gains revealed are quite impressive to go along with the new growl.
Normally, swapping cams in a mostly stock engine brings only small gains in horsepower and torque, but thanks to Ford's generosity in the cylinder-head department, that's not the case with Three-Valve engines. Copious amounts of air enter the cylinders by virtue of twin intake valves and the ever-changing cam timing. Technology has helped bring the Three-Valve modular engines to the next level with factory-supplied 300 hp from the tiny 4.6L displacement. Variable camshaft timing has helped produce low-end grunt and maintain a sparkling top-end power curve. One doesn't have to look hard to notice these cars run mid-to-high-13s right off the showroom floor, despite their heavy weight. A few bolt-on items and a computer retune will provide solid 12-second timeslips.
Mike Castaldo's '06 Mustang GT was largely stock, save for an array of bolt-on components. In stock trim, the GT drove the dyno wheels to 333 rwhp. The car benefits from a C&L Racer cold-air kit, a DiabloSport Predator (with JPC Racing tune), SLP Loud Mouth mufflers, Bassani long-tube headers, an x pipe system with high-flow cats, Granatelli coil-packs, a Meziere electric water pump, an MMR throttle body, and a Pro-5.0 short-throw shifter. | 
Gaining access to the camshafts is easy due to their location on top of the cylinder heads. The valve covers have to come off, and the wiring harness needs to be moved out of the way. All that's required to move the harness is to unhook the clips to the coil packs and fuel injectors. The fuel injectors remain in place; we just needed to move that portion of the harness. Unbolt the coil packs and remove them. | 
The valve covers are off, exposing the overhead camshaft setup. |
This month, we decided to take advantage of the better-flowing OEM heads by allowing more air into the cylinders via larger Comp Cams XE261H-15.5 (PN 127-300) camshafts. The lobes are nicely shaped and offer an increase in valve lift. Our new sticks carry a gross valve lift of 0.490 inch and 222 degrees of duration on the intake side of the valvetrain. Spent gases are expelled as the Comp camshaft lifts the valve off the seat a total of 0.480 inch and features duration of 235 degrees. The lobe separation is listed as 115.5 degrees. Bigger isn't always better, so be careful when selecting a camshaft for your hot rod. Comp went through consider-able testing to ensure these cams picked up power over the stock bumpsticks on a relatively stock engine, like the one we used for testing.
We would love to tell you the installation is easy and all you have to do is unbolt a few things here and bolt some stuff on there. That isn't the case with these camshafts. Due to their more radical nature, we were required to change the valvesprings for a couple of reasons. First, we heard some people had trouble with the stock springs snapping and cracking with the greater load. Second, the stiffer valvesprings are also required in order to control the valve movements at higher rpm. As the valvetrain increases speed with engine rpm, the valves will try to bounce and flutter, causing what is called "valve float." That is when the cam is not controlling the valve's opening and closing events. It leads to a loss in horsepower and possible engine damage. A stiffer valvespring keeps the proper load on the valvetrain, thus enabling the cam to control the valves' movements. We selected Comp Cams Beehive valvesprings (PN 26125-24) for the Three-Valve 4.6L engine and titanium retainers (702-24).
A special Ford tool is needed to remove the cam followers. The engine has to be set with the exhaust stroke coming up on the No. 1 cylinder. | 
The crankshaft keyway will be at the 12 o'clock position. | 
Cam followers look a lot like roller-rocker arms, and they serve a similar purpose in that they connect the camshaft to the valves. Modular engines, however, do not use pushrods and lifters to connect the camshaft to the valves. The overhead camshafts control the cam followers directly. |