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Comp Cams Ford Mustang Two-Valve Install - Mild-Too-Wild
Camming Your Two-Valve For Mild And Maximum Performance.
Because of the dynamic nature of the equation, camshafts are one of the most misunderstood performance components on any motor. This is especially the case on the overhead-cam modular 4.6L Ford motor. The difficulty is only compounded when you add things like forced induction or nitrous oxide to the mix. From an anatomical standpoint, the camshaft can be likened to the brain, as the profile determines how effectively (when and where) breathing takes place.
Camshafts are one of the major determining components of the effective operating range of the motor, too. Of course, the cam timing must be combined with the proper intake manifold, head flow, and primary length on the exhaust for optimum operation over a given rpm range, but the right cam can almost determine the character or personality of the motor. Stock or ultra-mild aftermarket cams will provide a dead-smooth idle, while more radical grinds can transform that mild-mannered motor into one incredible ride. The radical-ride route usually includes ill-tempered, cantankerous behavior until the motor comes on the cam(s), but such is the price for all that high-rpm heaven.
Many mod-motor enthusiasts at least understand the basics of cam timing. They realize that cam profiles come in a variety of different sizes. The high-lift and long-duration cams are much wilder and potentially more powerful than the wimpy production profiles. The problem arises when deciding to choose between these two extremes, especially for a daily driver.
The temptation is certainly there to go "big" on the cam profile. However, the cam profile must be selected not just for bragging rights on the Internet, but rather to work with your existing components. To be sure, adding the right cams to your otherwise stock motor can result in impressive power gains. Adding wild cams to your otherwise-stock motor may even result in a drop in power throughout most of the rev range, since the cams were designed to run effectively at 8,000 rpm and the rest of your stock components-intake runner length, head, and exhaust flow-sign off at just 6,500 rpm or less. This is especially true for Two-Valve modular motors. As a general rule, the closer to stock the remainder of the components, the milder the cam profiles that should be chosen. This means leave those weekend-warrior cams to the drag racers with lots of gear, aftermarket heads, and free-flowing exhaust. Instead, stick with mild, but effective, profiles that will offer power gains not just at high rpm, but throughout the desired rev range.
While normally aspirated cam choices are difficult enough, pick up just about any book on the subject of forced induction and skip to the chapter on camshafts. Likely as not, the recommendation will be to run stock cams or at least to stay away from the dreaded duration or overlap that can cause precious boost to escape past the exhaust valves. While blowers (and turbos) work fine on stock motors equipped with stock cam profiles, they (just like their normally aspirated counterparts) respond well to more aggressive cam timing. In fact, for most street applications, the camshaft chosen for a mild, normally aspirated motor will work equally well with a supercharger. Sure, you can tailor the specific cam timing for supercharged use, but the gains will be minimal at most mild boost and power levels run on the street (compared to a normally aspirated performance cam).
This is good news for enthusiasts, as choosing the right cams for a blower motor is as easy as selecting them for a normally aspirated motor, and, in many cases, are actually the very same cams. In most cases, the cam manufacturers list their applications and many have included profiles for forced-induction motors. But the N/A cams work well, too. This means you can install performance cams in your normally aspirated Two-Valve combination and then save up for that supercharger without fear of having to swap the cams again.
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.
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.
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.
It's important to point out that these exceptional peak power gains come with a trade-off in low-speed and midrange power as well as a drop in both driveability and fuel mileage.
To illustrate the difference in power offered by both mild and wild cam profiles, we took a modified 4.6 Two-Valve motor and ran three sets of cams. The first set was obviously the stock PI cams, which were run to establish a baseline. After running the stock sticks, we installed a set of mild cams, followed by a set of wild ones. We chose from Comp Cams Xtreme Energy line, though other cam companies also offer comparable mild and wild cam grinds. The idea behind the test was to illustrate the gains in power offered by the mild and wild profiles in comparison to the stock PI profiles. It's important to note that our test motor was set up to accept and benefit from these aggressive cams. The 4.6 Two-Valve combination featured a reciprocating assembly from Coast High Performance, including a Cobra steel crank, forged rods, and pistons. The forged pistons not only had valve reliefs to provide sufficient piston-to-valve clearance for our wild XE278AH cams, but also a static compression ratio of 10.3:1 when combined with the PI cylinder heads.
Since we wanted to properly demonstrate the potential of the cam profiles, we decided to use something other than the stock PI heads. The additional flow offered by porting would allow the 4.6 motor to take full advantage of the wilder duration specs, not to mention the 0.550 lift. The stock PI heads were treated to full porting from Total Engine Airflow (TEA). The TEA treatment improved the intake airflow numbers from 177 cfm to 225 cfm, while the exhaust flow numbers jumped from 126 cfm to 208 cfm. Certainly not huge flow numbers compared to the current crop of 5.0 heads, but the Two-Valves performed well, and TEA offers a Stage 3 program that can up the flow rate to over 240 cfm. Working in conjunction with the TEA heads was a set of ARP head studs and Fel-Pro head gaskets. Also used on this Two-Valve test was a set of Hooker long-tube headers, a stock PI intake, and an Accufab 75mm throttle body and inlet elbow. The combination (especially the intake choice) is important as this will affect the so-called ideal cam choice. Given the head flow limitations (even our excellently ported heads from TEA) of the Two-Valve configuration, high-rpm power was never in the cards for this combination, so the cam profiles should be chosen accordingly.
Using the FAST management system, a pan full of Lucas synthetic oil, and a set of Denso iridium spark plugs, we ran the Two-Valve first with the stock PI cams. So equipped, the modified 4.6 Two-Valve motor produced 346 hp at 5,800 rpm and 363 lb-ft at 4,700 rpm. As you will see, it isn't a surprise that the combination responded so well to the cam swap. After all, the stock cams were the only component holding back the power output, since everything else had already been upgraded.
The first set of Comp cams to be installed was the XE262AHs, which offered 0.550 lift on both the intake and exhaust, and a 226/230 duration split (measured at 0.050). The cams were ground with a 113-degree lobe-separation angle. Equipped with the XE262AH cams, the peak power numbers jumped to 386 hp at 5,800 rpm and 383 lb-ft at 4,800 rpm. Note that despite a sizable jump in duration, the power peak still occurred at 5,800 rpm, while the torque peak shifted by just 100 rpm (from 4,700 rpm with the stock cams to 4,800 rpm with the Comp cams). This is a clear indication that the intake manifold was controlling the effective operating range of this motor. These mild Comp cams never lost power compared to the stock cams, and they bettered or equaled the power output from 3,000 rpm all the way to 6,500 rpm.
Next up were the wild cams, namely the XE278AH grinds. They increased the cam duration over the milder XE262AH cams by roughly 16 degrees. Where the XE262AH cams sported 226/230 duration figures, the wilder XE278AH cams increased these duration (at 0.050) numbers to 242/246 degrees. The lift remained the same at 0.550 as did the lobe separation angle at 113 degrees. The sizable jump in duration increased the peak power output to 394 hp. But before you get all up in arms and order these wild cam profiles for your stock Two-Valve motor, know that in addition to not fitting in stock short-blocks (insufficient piston-to-valve clearance), the peak torque was actually down to 379 lb-ft.
Not only was the peak torque production down, but the larger XE278AH cams actually lost power compared to the stock PI cams up to 4,600 rpm. Compared at 4,500 rpm, the XE262AH cams offered an additional 25 lb-ft over the larger XE278AH cams. Only out at 6,500 rpm did the wilder XE278AH cams demonstrate their superiority, offering an extra 77 hp over the stock cam and 21 hp over the milder XE262AH cams. For the vast majority of street applications, the smaller XE262AH would be the clear choice, but the XE278AH cams would likely offer quicker e.t.'s and a higher trap speed if you kept the revs up. Of course, there's an intermediate set of cams between our mild and wild test profiles. Maybe the XE270AH cams are actually the hot setup.