One of the most misunderstood performance components on any Motor has to be the camshaft or camshafts. The difficulty is only compounded when you add things like forced induction to the mix. From an anatomical standpoint, camshafts can be likened to the brain, as the cam 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. Of course, the cam timing must be combined with the proper intake manifold, head flow, and primary header tube length for optimum operation over a given RPM range. Stock or ultra-mild aftermarket Cams will provide a dead smooth idle, while more radical grinds can transform that mild-mannered motor into one radical ride. The radical route usually includes ill-tempered, cantankerous behavior until the motor comes on the cam, but such is the price for all that high-RPM heaven.
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Many mod-motor enthusiasts at least understand the basics of cam timing. They realize that so-called “Saturday-Night Special” grinds are much wilder and potentially more powerful than the production cam profiles. The problem arises when deciding to choose between these two extremes, especially for a daily driver. The temptation is certainly to go big on the cam profile; after all, isn’t bigger always better? The problem with going big is twofold. The first problem is that the cam profile must be selected not just for bragging rights at the drive-in (or coffee house), but rather to work with your existing components. Adding the right cams to your otherwise stock motor can result in impressive power gains. Adding wild cams to your otherwise stock motor will likely hurt your power throughout the rev range and can even decrease peak power 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 6,500 rpm. As a general rule, the closer to stock the rest of your engine is, the milder the cam profiles should be. This means leave those weekend warrior cams to the drag racers and stick with mild but effective profiles that will offer power gains not just at high RPM, but also throughout the rev range. After all, what good is it to add 25 hp at the power peak only to lose 35 ft-lbs down at 3,000 rpm? Think for a moment about where (what RPM) you spend most of your time driving and choose a cam accordingly!
Degreeing the cams is every bit as important as a cam swap. Advancing and retarding the cams can yield huge power gains. It’s time-consuming, but ultimately worth it.
As difficult as cam swaps are on modular motors, what better way to illustrate the differences offered by six different cam profiles than to perform six different cam swaps on the engine dyno?
These Crower Stage 2 cams offered a sizable power gain over the stock ’03 Cobra cams on a Kenne Bell supercharged 4-valve.
While naturally aspirated cam choices are difficult enough, just look at any book on the subject of forced induction and skip to the section on camshafts. The recommendation will probably be to run stock cams, or at least to stay away from the dreaded duration or overlap that can cause all that precious boost to escape out past the exhaust valve. While blowers (and turbos) work fine on stock motors equipped with stock cam profiles, like their naturally aspirated counterparts, they respond very well to more aggressive cam timing. In fact, for most street applications, the camshaft chosen for a mild naturally aspirated motor will work equally well with a supercharger. Sure, you can tailor the specific cam timing for supercharged use, but the gains (compared to a naturally aspirated performance cam) will be minimal at most mild boost and power levels run on the street. This is actually good news for enthusiasts, as choosing the right cams for a blower motor is actually as easy as selecting them for a naturally aspirated motor – in many cases you can go with the very same cams. The manufacturers list applications for their cams and many have included profiles for forced induction motors, but the NA cams work well too. How do I know that NA cams work well on forced induction applications? Just check out the results of Tests 5 and 8.
Many mod-motor owners have steered clear of cam swaps, fearing the overhead cam configuration. Know that swapping cams in a 4.6L 2-valve or 4-valve motor is a bit more involved than performing the same task on a 5.0L V-8, but like anything else, once you’ve done it once or twice, 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. It is possible to add performance cams to your 4.6L (2-valve or 4-valve) 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. modular motors respond well to aggressive cam timing, though the 2-valve motors are ultimately head flow limited, so ultra-wild cam profiles will be less beneficial than on the free-flowing 4-valve motors. This chapter illustrates the gains offered on naturally aspirated and supercharged 2-valve and 4-valve combinations, but know that similar power gains are available on turbocharged mod motors as well. Don’t fear the cam swap 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.
The one thing missing in the modular world (a deficiency cured by the author after this testing) was the availability of adjustable cam sprockets. While cam swaps certainly offer power gains, they can be maximized only 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 bank. On 4-valve motors, we’ve measured differences in intake cam timing of 9 degrees (one cam was 9 degrees retarded relative to the other). Naturally, one setting is going to produce more power than the other, but the real concern is that the two banks of cylinders produce different relative power outputs. 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. 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 elsewhere, as advancing the cams (especially the intake) will likely improve low-speed power while retarding them will have the opposite effect. This will change somewhat after adding a blower or turbo, but it will be nice to be able to optimize the power output with adjustable cam sprockets.
The 2-valve cams are a tad easier than the 4-valve swap, but once you’ve performed the procedure once or twice, it isn’t any more technically difficult than a standard 5.0L V-8.
Test 1: Early 2-Valve GT: Comp Cams XE274H Camshafts
After spending some time tuning the base fuel and timing tables, we eventually coaxed this non-PI 4.6L engine to 260 hp and 341 ft-lbs of torque. We managed to match the flywheel rating of the new, more powerful PI GT motors, but before you get all in an uproar about happy dynos and exaggerated power numbers, remember that this reading was taken with long-tube headers, no MAF or air inlet system other than a 3-inch tube and cone filter, and no accessories. The idea was not to exceed the 260 hp offered by the late-model GT motor, but rather to establish a baseline to improve upon.
After I was confident about the repeatability of the baseline power numbers, I decided to start swapping some hard parts. First on the list for the early 4.6L was a set of performance cams. Wanting more than 5 to 10 extra horsepower, I decided to go big in terms of cam profiles and selected the largest Xtreme Energy grinds available for the early 4.6L GT motor. The dual-pattern XE274H cams offered a 236/240-degrees duration split, along with .500 inches of lift for both the intake and exhaust. A wide 114-degree lobe separation angle helped tame the cam somewhat, but the duration ensured that these cams lived up to the description of “Hot Street Cams” given in the Comp Cams catalog. Comp Cams also recommended steeper rear-end gears, a higher stall speed (if automatic equipped), and computer upgrades (otherwise known as getting a chip or tune). Our F.A.S.T. programmable ECU obviously fell under the last category, so we felt confident that we could provide any fuel or timing changes that were needed. The new cam profiles required a valvespring upgrade, so Comp Cams supplied a set of 26113-16 springs to provide sufficient seat and open pressure (along with the necessary coil-bind clearance) to ensure proper valve control.
Though designed to operate effectively from 2,000 rpm to 6,000 rpm, we found out in testing that the stock non-PI GT intake manifold kept peak power well below 6,000 rpm. Still, I had high hopes for the cam upgrade. After installing the springs and XE274H cams, the peak power jumped from 260 to 301 hp. The early GT was now making at least as much as (and possibly more than) a later PI GT motor. The peak torque was up as well, by 5 ft-lbs. Not surprisingly, the motor lost a bit of power below 3,400 rpm, but beyond that it was all power. With an effective power band of 3,500 to 5,500 rpm, these cams would do nothing but improve acceleration. With as much as 50 extra horsepower available thanks to the cam swap, the extra acceleration would be significant. In fact, I’d have to say that the wimpy stock intake and heads were now holding back this early GT motor from making serious power.
Comp Cams recommended a spring upgrade to go with their XE274H cams.
It’s important to degree your new cams and make sure they’re right on. The last thing you want to do is take everything back apart.
Stock Early GT Cams vs. Comp XE274H Cams (Horsepower)
These are the kinds of power gains you dream about when installing performance cams. The Xtreme Energy XE274H cams from Comp Cams added as much as 53 hp to the otherwise stock non-PI 4.6L
Stock Early GT Cams vs. Comp XE274H Cams (Torque)
Note from the torque curve that the wilder cam profiles cost some torque below 3,400 rpm, but significant gains were achieved from 3,500 to 5,500 rpm. The Xtreme Energy cams allowed this early 4.6L to produced PI power and torque numbers.
Test 2: PI 2-Valve GT: Six Sets of Comp Cams Xtreme Energy Camshafts
If you learn anything from this chapter on performance camshafts it should be that wilder cam timing does indeed improve 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. The intended application should dictate the cam choice, but the chosen cam may also reflect your personality. Do you have the crust trimmed from your bread while you’re watching the cooking channel? Then a stock cam with its (pre-prison) Martha Stewart smooth idle is probably for you. If, on the other hand, your tastes tend more toward Tater Tots and beer while fast-forwarding to the Seth Enslo jump on Crusty Demons of Dirt, then drop right to the bottom of the cam page where the big ones are. Like you, the idle is a little rough around the edges, but things start to kick ass when you come up on the cam. Crusty Demons notwithstanding, the intended use is actually the most important factor when choosing a cam. Obviously, the cams chosen for a drag-race motor would differ from those optimized for street use or even a road-race application.
Also consider 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 6,000 rpm. In all likelihood, most people won’t be building dedicated (single-purpose) motors and will instead have existing stock or mildly modified motors that they deem in need of performance cams. Given that the vast majority of modular motors are of the 4.6L 2-valve variety, this test was designed to help you select the proper cam for your combination. It’s impossible to run every cam in every conceivable combination, but I was able to test every one of the six different Comp Xtreme Energy (both PI and non-PI) sets of cams against the stock cams in a modified 4.6L 2-valve motor.
Though all of the Comp Xtreme Energy cams offered power gains over stock, they did so differently, and in every case, the power gains were accompanied by losses in power somewhere in the rev range (usually down low). The milder cam profiles (like the 262H and 262AH) traded very little torque down low (15 to 18 ft-lbs) for the power gains achieved above 4,500 rpm (48 to 58 hp). The larger profiles (like the 278AH) dropped 35 ft-lbs down low, but offered as much as 77 hp at 6,500 rpm. As indicated earlier, the choice is ultimately up to the vehicle owner. Just be sure that you are honest about the intended use, and don’t be tricked by the big power numbers out at 6,500 rpm. Your street motor will spend a lot more time driving around from 2,500 rpm to 4,500 rpm than at wide open throttle at 6,500 rpm. Also realize that this DSS-built test motor featured CNC-ported heads from TEA, a PI intake with Accufab 75-mm throttle body and inlet elbow, and a set of Hooker headers. The power probably wouldn’t be as great on a milder combination. Be sure to check out all of the following graphs, as this test involved six different sets of Comp cams, as well as the stock PI cams.
You can swap 4.6L 2-valve cams with the engine in the car, but it’s easier with the engine on the dyno. It’s a little more complicated than a 5.0L cam swap, but it’s definitely not impossible.
For this test, we ran six different sets of Comp cams against the stock PI cams. Each offered additional horsepower but lost torque down low. Check out the following dyno graphs to help you decide which cams are right for your application.
PI 2-Valve GT: Stock PI Cams vs. Comp XE262H Cams
The smallest of the non-PI cams, the XE262H profiles offered significant power gains above 4,500 rpm. The cams were worth an additional 48 hp on this combination and a good 25 to 30 ft-lbs. The tradeoff in low-speed (from 2,500 to 3,500 rpm) torque was minimal, roughly 15 to 18 ft-lbs from 2,500 to 3,000 rpm.
PI 2-Valve GT: Stock PI Cams vs. Comp XE268H Cams
Stepping up to the slightly larger (still non-PI) XE268H cams offered an additional 58 horsepower, but the gains started at 4,550 rpm. Note that the losses were greater down to 3,500 rpm, and this trend continued down to 2,500 rpm as well.
PI 2-Valve GT: Stock PI Cams vs. Comp XE274H Cams
The largest non-PI cams (XE274H) were actually the first Comp modular cams I ever tested. They have proven themselves powerful time and time again, despite offering only .500 lift (the PI cams offer .550 lift). The XE274H profiles improved the power output of the DSS 4.6L by 62 hp, but the trend toward increasing losses below 3,000 rpm continued, as the XE274H cam dropped over 20 ft-lbs of torque below 3,200 rpm.
PI 2-Valve GT: Stock PI Cams vs. Comp XE262AH Cams
The XE262AH cams are probably my favorite street cams for the 2-valve 4.6L. These cams offered an additional 55 hp and showed power gains all the way down at 3,700 rpm. The losses were minimal below 3,100 rpm, yet the motor pulled strongly all the way past 6,500 rpm.
PI 2-Valve GT: Stock PI Cams vs. Comp XE270AH Cams
The middle PI cams (XE270AH) offered an additional 60 hp at 6,500 rpm over the stock cams, but the losses increased down low compared to the XE262AH. Where the XE262AH cams offered power gains starting at 3,700 rpm, the larger XE270AH cams bettered the stock cams at 4,400 rpm.
PI 2-Valve GT: Stock PI Cams vs. Comp XE278AH Cams
The largest of the XE series cams are the XE278AHs. The largest cams dropped power to the stockers up to 4,600 rpm, but added 77 hp at 6,500 rpm. Unlike most of the other cams, the XE278AH cams fell off very little after the power peak at 6,100 rpm.
Test 3: Ford Racing Supercharged PI 2-Valve GT: Comp Cams XE262H Camshafts
The Sean Hyland Motorsport (SHM) 4.6L test motor was one of the more desirable (1999-’04) Power-Improved (PI) engines. It featured a forged reciprocating assembly (stock compression) topped off with bone-stock PI heads, cams, and composite intake manifold. The SHM motor was topped off with a Ford Racing supercharger assembly consisting of an M90 roots-style supercharger and dedicated aluminum intake casting. The supercharger intake features long intake runners designed to optimize power (and torque) production up to 6,000 rpm. The supercharger would provide the additional airflow in the form of boost pressure, but the intake runner length is critical (in both NA and blown applications) for maximizing torque. Combining the immediate boost response of a positive displacement blower with optimized runner length makes for one impressive power curve. In addition to the blower, the motor was also equipped with a 70-mm Ford Racing throttle body, a smaller blower pulley to increase the boost pressure, and 36-pound injectors run by a F.A.S.T. engine management system. The SHM 4.6L was also equipped with a set of Kooks 1⅝-inch stainless steel headers, an electric water pump, and an MSD coil pack.
To illustrate the gains possible with a cam change on a supercharged application, I swapped out the stock PI cams for a set of Xtreme Energy 262H cams (actually designed for the non-PI heads). The main difference in the PI and non-PI cams is the lift value. The PI heads are set up to accept higher (.550 inch) lift cams than the non-PI (.500 inch) versions. The non-PI cams can be run in the PI heads with no trouble, but the reverse is not true without ensuring adequate retainer-to-seal and coil bind (valvespring) clearance. The XE262H cams offered .500 lift (both intake and exhaust) but a dual-pattern duration split. The intake featured 224 degrees of duration and 232 degrees of exhaust duration (@ .050). The wide 114-degree lobe separation angle ensured a broad curve and a relatively smooth idle given the durations specs. The Xtreme Energy cams worked fine with the stock valvesprings, though Comp does offer a valvespring upgrade for both the 2-valve and 4-valve modular motors.
Though originally designed for a naturally aspirated combination, these mild Comp XE262H cams added horsepower and didn’t give up any torque on a supercharged application.
This supercharged 4.6L PI was tested with the stock PI cams and then again with some Comp XE262H cams. The more efficient Comp cams caused the boost pressure to drop to 6.9 psi.
Installing the cams wasn’t terribly difficult, but this wasn’t my first time. The XE262H cams have been previously tested on a modified naturally aspirated motor and shown to offer impressive power gains on the order of 30 to 35 hp. How well do these “naturally aspirated” cams work on our blown 4.6L? Well, they worked equally well, upping the peak power from 405 to 436 hp (both at 6,000 rpm). In fact, the Comp XE262H cams not only improved the peak power and torque numbers, they didn’t lose power anywhere. It’s interesting to note that when tested naturally aspirated, the Comp cams showed power improvements starting at 4,500 rpm, while the gains on this supercharged application started as low as 3,300 rpm. Installing the cams actually reduced the peak boost pressure to just 6.9 psi. The drop in peak pressure is not from boost escaping out the exhaust of the wilder cam timing, but rather from the increase in efficiency. The more powerful the naturally aspirated motor, the lower the boost pressure at any given blower speed.
Supercharged PI 2-Valve GT: Stock Cams vs. Comp XE262H Cams (Horsepower)
As expected, the XE262H cams offered impressive power gains. Out near 6,000 rpm, the Comp cams bettered the stock PI cams by over 30 hp.
Supercharged PI 2-Valve GT: Stock Cams vs. Comp XE262H Cams (Torque)
Perhaps the most impressive thing about this cam test was that there was no tradeoff in power with the Comp cams on this supercharged combination. The wilder cam timing simply improved the power output from 3,300 rpm all the way to 6,000 rpm.
Test 4: Vortech Supercharged Early 2-Valve GT: Comp Cams XE274H Camshafts
This supercharged cam comparison was actually a retest (of sorts) on the Comp 4.6L 2-valve cams used in Test 1. The idea was to demonstrate whether the XE274H cams originally designed for a naturally aspirated combination would work well on a supercharged motor. Due to a snafu with the stock Mustang PI cams (one was lost), I was forced to compare the XE274H cams to a set of 4.6L truck cams that I got at the last minute from Accufab’s John Mihovitz (at midnight no less – thanks John).
As with most of the testing run on the engine dyno, this modified 4.6L motor was tuned using the F.A.S.T. engine management system. In no way does that make the results less than applicable for street motors running the factory computer. Custom programming is readily available for the factory ECU and should be considered when installing any type of forced induction, whether modified or stock. I shudder to think of installing a supercharger or turbo on any motor and immediately taking it out on the street and stomping on the throttle. Detonation will kill even the strongest forged pistons, where proper tuning will allow you to run trouble-free for years. The F.A.S.T. system allowed us to run any size injector and run without the mass-air meter. Since we were primarily concerned with wide-open throttle tuning (and minor associated transition throttle), the F.A.S.T. system was definitely the way to go. Tom Habryzk from Westech had each combination up and running in no time. The procedure with the F.A.S.T. system was to load the motor at 3,000 rpm to check air/fuel. If the motor was lean at any throttle position, fuel was added via the fuel tables. The total timing was kept at a safe 18 degrees during tuning. This procedure was repeated at 3,500 rpm, 4,000 rpm, and then 4,500 rpm until we reached the maximum engine speed. Only after establishing a safe fuel curve did we load the motor and run a sweep test through the rev range.
Do Comp XE274H cams work on a supercharged application? We’re about to find out.
The modified 4.6L (TEA-ported heads, PI intake, and Hooker headers) was run first with the stock 4.6L truck cams and then again with the Comp XE274H cams. Unfortunately, no cam timing adjustments were made to optimize the power; both were installed straight up, using the factory (no adjustable) cam sprockets. Not surprisingly, the two cam profiles required decidedly different fuel cures, as the motor produced a great deal more power with the Comp cams than with the stock cams. When we tested the XE274H cams against the stock 1998 GT cams, we noticed that the motor produced more power with the stock cams up to 3,500 rpm, at which point the Comp cams took over. The very same thing happened on the supercharged motor, as the stock cams made more power from 3,000 rpm to 3,500 rpm, but fell off dramatically thereafter. Equipped with the stock cams, the Vortech supercharged motor produced 550 hp and 505 ft-lbs of torque. With the Comp XE274H cams, the engine made 655 hp and 557 ft-lbs. Imagine, a cam change worth 105 hp and 61 ft-lbs of torque. Keep in mind that these power numbers were generated on the stock 1998 short block with only a set of ARP head studs and Fel-Pro gaskets. Careful tuning is the reason we still have a solid 4.6L eager and ready to test!
These Comp XE274 cams were tested against a set of stock 2-valve truck cams.
Supercharged Early 2-Valve GT: Non-PI Cams vs. Comp XE274H Cams (Horsepower)
When every other component on the motor has been optimized, the stock cams really restrict the power output of a supercharged 4.6L. Installing the Comp XE274H cams in place of the stock 4.6L truck cams upped the power output by over 100 hp.
Supercharged Early 2-Valve GT: Non-PI Cams vs. Comp XE274H Cams (Torque)
As was the case with the naturally aspirated test, the stock cams offered slightly more torque up to 3,500 rpm, but beyond 4,000 rpm, it was all Comp cams. The gains down low paled in comparison to the power improvements from 4,000 rpm to 6,000 rpm. Oddly enough, the boost changed very little with this cam change.
Test 5: Naturally Aspirated ’03 4-Valve: Cobra Cams vs. Comp Cams XE262AH Camshafts
This test compares the stock ’03 Cobra cams and a set of Comp XE262AH cams. Though originally equipped with an Eaton supercharger, the low-compression ’03 Cobra crate motor was equipped with a 2001 Cobra intake manifold (and no supercharger). This cam setup was also tested with the Eaton and Kenne Bell superchargers, so be sure to check out Tests 7 and 8. To illustrate the gains offered in naturally aspirated trim, the motor was equipped with the F.A.S.T. management system, a Meziere electric water pump, and Flow-Tech long-tube headers (no mufflers). The motor was tuned for a 13.0:1 air/fuel ratio and 28 degrees of timing. The low-compression 4-valve motor produced 369 hp at 6,000 rpm and 377 ft-lbs of torque at 4,900 rpm. Equipped with the stock cams, the power curve pulled strong up to 5,000 rpm where it flattened out until 6,500 rpm. Despite the low compression, the torque output exceeded 350 ft-lbs from 3,600 to 5,400 rpm. Though this was pretty decent considering the low compression, I knew there was much more power to be had with the right set of performance cams. With the baseline tests out of the way, we tore into the Cobra motor to perform the cam(s) swap.
We checked the position of the stock ’03 Cobra cams before we removed them from our naturally aspirated test engine. The right and left intake lobes were as much as 7 degrees off, while the exhaust lobes were just 3 degrees off.
After we installed the Comp XE262AH cams, we degreed them and checked them against the cam card. The cams provide a big bump in horsepower, along with a very healthy sound.
Before I get to the results of the cam swap, it’s important to mention that I checked the position of the stock cams and degreed aftermarket cams before testing. After establishing the baseline power numbers, I installed the degree wheel assembly on loan from Accufab to see how well the factory set up the ’03 Cobra crate motor. As it turned out, the stock cams were way off. The right and left intake lobes were as much as 7 degrees different. The exhaust lobes were a little better at just 3 degrees, but we couldn’t help wondering how much power was lost due to the stock cams being so far out of whack.
After installing the Comp cams, we went to the effort of degreeing the cams to see how they stacked up against not only the stock cams but also against the supplied cam card. Right to left the Comp cams were perfect, with both intake cams checking in at 117 degrees. The exhaust cams were off by only 1.5 degrees side to side. The odd thing was that the cam card provided the specs at 112 degrees, roughly 5 degrees off from where our cams were currently installed. How this affected power output was anyone’s guess, but we’ll be looking into it in the very near future. With the new Comp XE262AH cams, we noticed the motor had a slightly more aggressive idle. After the first power pull we could see why. The Comp cams upped the power output from 369 hp to an amazing 426 hp at 6,300 rpm. Since most of the power gains came past 5,000 rpm, the peak torque was up only slightly to 390 ft-lbs. If you check out the graphs, you’ll notice that there was a slight loss of low-speed torque from 3,500 to 4,900 rpm, though the torque losses were more than offset by the tremendous power gains past 4,900 rpm.
’03 Cobra: Stock Cams vs. Comp XE262AH Cams (Horsepower)
The naturally aspirated ’03 Cobra crate motor responded very well to the Comp XE262AH cams. Equipped with the stock cams, the power leveled off at 5,000 rpm but continued to climb past 6,000 rpm with the Comp cams. The Comp cams were worth an extra 63 hp.
’03 Cobra: Stock Cams vs. Comp XE262AH Cams (Torque)
As is usually the case with cam changes, the huge power gains achieved past 5,000 rpm cost a little bit of torque down low. Despite being off side to side, the stock ’03 Cobra cams bettered the Comp cams from 3,000 to 5,000 rpm, but only by 15 to 20 ft-lbs. Additional cam tuning might have decreased the torque loss down low.
Test 6: 4-Valve Cobra: Degreeing Comp XE262AH Camshafts
Degreeing the cams is very important if you want to make as much power as possible. It’s imperative that even the factory cams be matched side to side. I’ve seen the cam timing be off by 8 or 9 degrees.
This test features the 4-valve Cobra motor built by Sean Hyland. The 4.6L features a forged steel crank, rods, and flat-top pistons. The flat-top pistons pushed the static compression ratio to near 10.5:1, which is just about perfect for street use. The flat-top design also provided optimum flame travel without interference from a dome. We topped the short block with a set of Ford Racing FR500 heads that had been worked over by Total Engine Airflow, a ported 2001 Cobra intake, and a set of Comp XE262AH cams (the largest that will fit without piston-to-valve interference). The specs on the Comp cams checked in at .425 inches of lift, 226 degrees of intake duration, and 224 degrees of exhaust duration (@ .050). The cams featured a 114-degree lobe separation, though adjusting the cam sprockets can change this. The engine was set up with a stock 4-valve Cobra throttle body and a set of Hooker long-tube headers feeding 3-inch open exhaust. We ran an electric water pump and no other accessories. The air/fuel and timing curves were dialed in using a F.A.S.T. management system. After playing with various timing curves, we were finally rewarded with peak numbers of 426 hp at 6,100 rpm and 394 ft-lbs of torque at 5,000 rpm.
While the power numbers looked good, I was actually expecting a bit more power given the compression, ported heads, and Comp cams. John Mihovitz suggested that we check and adjust the cam timing. Using his years of mod-motor experience, John degreed the cams in their current position and discovered that the intake cams were unbalanced side to side by 6.5 degrees. The driver’s side checked in at 114.5 degrees, while the passenger side intake cams were at 108 degrees. Both exhaust cams were even at 113 degrees. To improve the power output of the 4-valve test motor, John advanced both intake cams to 107 degrees. It’s imperative that even the factory cams be matched side to side. I’ve seen the cam timing be off by 8 or 9 degrees. With the two sides so different, one bank of cylinders will certainly be out-powering the other. This is not a desirable situation for maximum power or smooth operation.
We checked our Comp cams and found that the intake cams were unbalanced side to side by 6.5 degrees. The driver’s side checked in at 114.5 degrees, while the passenger-side intake cams were at 108 degrees. Both exhaust cams were even at 113 degrees.
After adjusting the XE262AH cams, I ran the SHM 4-valve Cobra motor on the dyno once again. After adjusting the cams, the power jumped up significantly. Dialing both intake cams to 107 degrees resulted in a gain in peak power of 9 hp, though the largest horsepower gain registered from 3,500 rpm to 6,500 rpm was 14 hp. Even more important in the jump in peak power was the fact that the power curve improved throughout the rev range. In fact, advancing the cam(s) resulted in more of a gain at 3,500 rpm than at 6,500 rpm. This is to be expected, as typically advancing the cam timing will increase low-speed power while retarding the cams will improve top-end horsepower. True to form, advancing the cams (even just one intake cam) improved the torque production by as much as 22 ft-lbs. It is this attention to detail that makes the difference between a good-running Cobra and an average one. It also helps explain why some stock Cobras are faster than others right off the showroom floor.
Degreeing Comp XE262AH Cams: 4-Valve Cobra (Horsepower)
When you add power from 3,500 rpm (and below if we bothered to run the motor there) to 6,500 rpm, chances are that you’ve done something right. With the help of John Mihovitz, advancing the cams from 113 to 114 degrees to 108 degrees was worth a solid 14 hp and a consistent 10 to 12 hp through most of the power curve.
Degreeing Comp XE262AH Cams: 4-Valve Cobra (Torque)
As expected, advancing the cams paid larger dividends at lower engine speeds. Altering the cam timing by nearly 6 degrees increased the torque production by as much as 22 ft-lbs. I guess Mr. Mihovitz knows a thing or two about mod motors.
Test 7: Eaton Supercharged ’03 4-Valve Cobra: Comp Cams XE262AH Camshafts
Like their selections for the 2-valve mod motors, Comp Cams offers a wide variety of different cam profiles. Not all 4-valve 4.6L motors (or their owners) will respond to the same ca
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