After running the stock PI...
After running the stock PI cams, we were rewarded with 346 hp and 363 lb-ft of torque. Before removing the stock cams, we lined up the markings on sprockets and chains to position the motor at TDC.
For some reason, many mod-motor owners have steered clear of cam swaps, fearing the overhead cam configuration. Know that swapping cams in a 4.6L Two-Valve motor is a bit more involved than performing the same task on a typical 5.0 V-8, but like anything else, once you've performed the task a time or two, you'll wonder why you avoided all that extra power for so long. As is usually the case, stock cam profiles leave something to be desired in terms of maximizing power.
The stock Two-Valve cams were never designed with maximum power production in mind, and as such, there's plenty of power to be had from a set of performance cams. It's possible to add performance cams to your 4.6 Two-Valve motor and gain power across the rev range, though the wilder (more powerful) profiles will usually cost some low-speed power in trade for the significant gains in midrange and top end. The modular motors respond well to aggressive cam timing, though the Two-Valve motors are ultimately head-flow limited, so ultra-wild cam profiles will be less beneficial than on the free-flowing Four-Valve motors. Don't fear cam swaps on a mod motor, just take things slow and have the factory manual handy as a reference. In a day or so, your motor will be up and running with a nasty new attitude.
Off came the stock cams to...
Off came the stock cams to make way for the XE262AH grinds from Comp Cams.
While cam swaps certainly offer power gains, they can be further maximized after degreeing the cams. In the case of modular motors, the cams on the right bank of cylinders are not always in alignment with the cams on the left when they leave the factory. On Four-Valve motors, we've measured differences in intake cam timing of 9 degrees (one cam was 9 degrees retarded relative to the other).
Differences in cam timing on the Two-Valve motor will affect both the intake and exhaust (side to side). Naturally, one setting will produce more power than the other, but the real concern is that the two banks of cylinders produce different power. Obviously, this unbalanced power production is not desirable, but the only way to cure it is to degree and adjust (synchronize) the cam timing side to side. The power production can be further enhanced by advancing or retarding the cams in unison, to find optimum power. Additional gains will likely come at the expense of power production elsewhere in the curve, as advancing the cams, especially the intake, will likely improve low-speed power, while retarding them will have the opposite effect.
The stock and XE262AH cams...
The stock and XE262AH cams shared the same 0.550 lift numbers (both intake and exhaust), but even these mild Comp cams offered much more duration. The XE262AH cams featured a 226/230-degree duration split and a 113-degree lobe-separation angle.
If you come away with anything from this article, it should be that wilder-than-stock cam timing does indeed improve power. That really should come as no surprise. After all, why would cam companies go to such trouble to design and build cam profiles if they didn't add any power? In reality, the question isn't so much whether performance cams will add power, but more of which cam is the right one for your application? In fact, the intended usage is actually the most important factory when choosing a cam.
Obviously the cam(s) chosen for a drag-race motor would differ from those optimized for street use or even a road-race application. Combined with intended usage is the existing engine combination, as the cam profile must work in conjunction with the intake manifold, cylinder heads, and exhaust system to produce maximum power in a given rpm range. It makes no sense to install cams designed to make peak power at 7,500 rpm when the rest of the components sign off at just 6,000 rpm. In all likelihood, most Two-Valve owners will not be building dedicated (single-purpose) motors, and will instead have existing stock or mildly modified motors that they deem are in need of performance cams. Rest assured that even the mildest of performance cams offered by the many cam companies will offer significant power gains over the factory profiles-just resist the temptation to run the wildest cams because they promise the biggest peak power gains.