Michael Galimi
August 1, 2008
The S197 Mustangs are the most technically advanced ponycars to hit the streets. One of the biggest features on the Three-Valve engine is the use of Variable Camshaft Timing (VCT). We tested Comp's latest camshafts designed to get the most from the newest member of the modular motor family.

In prison, when the general population gets out of control, guards institute a lockdown. When those bells go off, inmates are secured and activity is frozen. It helps the guards maintain order and keep control. The dictionary defines lockdown as "a state of containment or a restriction of progression."

Recently, Comp Cams instituted its own form of lockdown when engineers designed a special backplate for the Ford Three-Valve engine's camshafts. By limiting the advance/retard capabilities, Comp was able to introduce a new lineup of camshafts with aggressive specs. The Cam Phaser Limiter kit is not a total lockout of Ford's variable cam timing events, but it severely reduces the cam's ability to be retarded by the computer system at higher rpm levels.

Variable camshaft timing (VCT) in the Three-Valve engine is a big advancement for Ford V-8 engines. As you know, the cam (or cams) in any engine control the opening and closing of the valves. Therefore, cams are designed to optimize airflow into the engine, as per the given application. By allowing the cam timing to be altered while the engine is running, you essentially can make the engine more efficient over a wider range of rpm. This is what VCT does, and to accomplish it, Ford designed a series of oil channels through the heads and camshafts to feed pressure to camshaft phasers at the end of the camshafts. The engine-management system commands a pair of solenoids to advance or retard the camshaft timing (by as much as 60 degrees in relation to the crankshaft) based on driving conditions.

Jim D'Amore III's Saleen clone features a 298ci engine. It has JDM ported Three-Valve heads, a stock intake, a steel crankshaft, Manley rods, and forged pistons (11:1 compression). It made 350 rwhp and 366 rwtq, with the stock cams in place. The stock sticks were seriously hampering performance.

Adjusting camshaft timing while the engine is running offers several unique advantages over conventional fixed camshaft timing. On top of Ford's list is fuel efficiency. Nowadays, that's critical, as manufacturers are working towards the federal government's mandated 34-mpg fleet average fuel economy. This is to be accomplished by the year 2012. Your author's '07 automatic-equipped, near-stock Mustang GT regularly gets 25-26 miles per gallon in strictly highly cruising scenarios, showing its effectiveness.

Performance-wise, VCT is effective because valve timing (the opening and closing of the valves) can be optimized for a partic-ular situation. Have you ever wondered why Three-Valve engines have a broader torque curve than Two-Valve and Four-Valve modular engines? The bottom-end torque gains aren't the only advantages, as Three-Valve engines are rev-happy as well.

"The cam timing is advanced from the factory to help low-end torque," says Jim D'Amore Sr. of JDM Engineering. "The factory sets the cam timing base at 7 degrees."

Cutting right to the good stuff, our test vehicle picked up 51 peak horsepower. The real story is that we saw 81 more rear-wheel horsepower under the peak! Swapping to the Comp SPR Stage 3 camshafts helped our test vehicle go from an 11.51 at 114 down to a best of 11.15 at 119 mph.

As the engine climbs in rpm, the computer retards the camshaft to gain top-end power. It retards the camshaft 9 degrees in the upper rpm levels, bringing total camshaft timing to negative 2. The general rule of thumb is that advancing the camshaft timing creates better low-end power, while retarding the cam timing will help the engine make greater top-end power. Ultimately, this leads to more efficient cylinder filling over a wider range of operation. Pushrod, Two-Valve, and Four-Valve engines are stuck with fixed camshaft timing, forcing you to make a compromise when advancing and retarding the cam. VCT allows us to have our cake and eat it, too.

Now that we're hyped up on the variable cam timing, it's time to deflate its too-good-to-be-true abilities. VCT works great in the stock application, but is it the best thing to happen since sliced bread? One downside is that because the timing events are altered, installing big-lift or duration cams can cause piston-to-valve clearance problem. Obviously, the factory doesn't care much about aftermarket camshafts, so the clearance with larger camshafts wasn't factored in when Ford designed the Three-Valve mod motor. All is not lost, though, as Comp has now released a limiter kit, enabling your engine to continue utilizing VCT, while keeping the valves clear of the pistons when they near top dead center. It merely limits the cams' advance and retard movements to prevent interference with moving pistons.

The Comp Phaser Limiters don't allow the cams to vary more than 20 degrees (in relation to the crank) in either direction. Remember, the unrestricted stock combination allows as much as 60 degrees. The Comp Phaser Limiters allow for a more aggressive profile, allowing the camshaft to unlock more horsepower from your mod motor from greater lift and duration. According to Comp Cams' Brian Reese, "Limiting cam movement through just the computer is only good on paper. Mechanically limiting them to 20 degrees of movement prevents any problems. We've found that phasers are less controllable at low oil pressures or during startup. Another uncontrollable situation is during aggressive transient times--think shifting, dropping the clutch, panic stops, and so on. The cam phasers can move beyond their commanded position because of mechanical inertia they experience. During these times, they can do things they're not programmed to do."

The camshafts are from the XFI line and dubbed SPR, which stands for Springs and Phaser Mods Required. Installing the SPR Stage 1 and Stage 2 cams in stock bottom-end combinations will be useful--just be sure there are better valvesprings to handle the greater rpm and load. The SPR Stage 3 cams are designed for engines with aftermarket pistons, more compression, and heavily ported heads.

All SPR camshafts require Phaser Limiters, and cam timing is set at 15 degrees advance. As the engine climbs and the computer retards the camshaft, the same 9-degree retard (the stock adjustment) takes place, and the total camshaft timing works out to be positive 6 degrees. As mentioned earlier, the stock cam is set at 7 degrees advance, 9 degrees removed, and the total at high rpm is negative 2 degrees. With the camshafts being limited to 20 degrees of movement (in relation to the crank), there's a need to tune the computer system to account for the limited movements.

Our test subject is a car that should be familiar with regular readers--Jim D'Amore III's '06 Mustang. We've become obsessed with his naturally aspirated combination. It's easy to fall in love with this Stang because of its simplicity and effectiveness as a dragstrip stormer and street brawler. The combo is sedate, yet runs low-11s at 119 mph when the money's on the line. This envy-ridden machine consists of a JDM-built 298-inch stroker engine, which uses a 3.750-inch stroke crankshaft, Manley rods, and forged pistons (11:1 compression). The heads feature a JDM-spec port job and larger Manley intake and exhaust valves. The intake manifold remains stock but breathes easier thanks to a C&L Racer cold-air intake and a larger SCT MAF sensor. Exhaust is pretty much par for the course with Kooks long tubes, an x pipe system, and a MagnaFlow after-cat exhaust system.

Surprisingly, the stock camshafts were utilized for the better part of 2007, and they worked well with the increase in cubic inches, compression, and cylinder-head flow. "At the time we did the engine," D'Amore Sr. says, "I wasn't impressed with anything on the market. I figured we'd leave the stock cams in place until something came out." In that trim, the Saleen clone spun the DynoJet chassis dyno to a max power reading of 350 rwhp and 366 rwtq through a stock auto trans, and ran a best e.t. of 11.51 at 114.50 mph.

VCT is awesome, but its ability to adjust cam timing also causes an interference problem when adding larger camshafts. To combat this problem, Comp Cams released its Cam Phaser Limiter kit. It reduces the cams' movements from 60 degrees (in relation to the crank) to a mere 20 degrees.

The Stage 3 camshafts feature 0.540-inch lift on the intake and 0.561-inch lift on the exhaust. Lobe separation is listed as 112 degrees, while the duration checks in at 242 (intake) and 252 (exhaust). Because the cams are designed to make power higher in the rpm band than stock, a minimum of 3,000-stall speed in your torque converter is required, as are a minimum of 4.10 gears for full optimization. With a manual transmission, just a gear change to 4.10 or higher is needed. Likewise, the Stage 3 camshafts are designed for engines with a built short-block.

After swapping the sticks, we noticed an aggressive idle emitting from the center-exit exhaust system. The car growled, and its presence was definitely known, especially when D'Amore III rolled the car into the dyno bay. Things were about to get interesting, but first the elder D'Amore had to make provisions in the ECU before we could have fun. "I had to change the specs to prevent the computer from going into the fail-safe mode," he says. "The computer will change the cams up to 60 degrees, but I change that number in the computer to only allow up to 20 degrees. If the cams can't go as far as 60 degrees, the computer will sense it and throw the code PO340."

When the hammer was dropped, the car revved quicker and higher thanks to the new cams, and the stroker ripped off a best of 401 rwhp and 379 rwtq. The peak power picked up 51 hp, but under the curve we saw as much as 81 hp. Torque output also increased, as peak torque jumped by 13 rwtq, while we saw as much as 64 rwtq in the middle part of the torque curve.

The plate bolts on to the factory cam sprocket.

On track, the story was similar, as the Mustang ran quicker and faster than ever before. The 3,500-pound Stang ripped down Englishtown's track in only 11.15 seconds at a terminal speed of 119 mph (it later went 120). That was all accomplished with the stock 5R55S transmission and a TCI 3,000-rpm stall speed torque converter. The rear gears checked in at 4.56, but a set of 4.88s is up next and should get the GT closer to the 10s--without a power adder!

Our test car might be a bit more radical than the average S197, but utilizing a better set of camshafts will benefit most Three-Valve mod motors. After all, there are 14 different grinds on the Comp Cams shelf. The company has now given you control over VCT in order to unlock the potential from your free-breathing Three-Valve combination.

Navigating Comp's Line of Three-Valve Camshafts
OK, not everyone has a stroker with ported heads, so Comp designed many cams for all applications. If you want milder camshafts, Comp offers a variety under the XFI camshaft lineup. The first set is nicknamed NSR (No Spring Required). They're designed for blown or naturally aspirated engines, and best of all, you don't have to change springs, thus simplifying the install (not to mention saving you money, too). There are two stages each for N/A and blown combos, for a total of four different cams designed for mild applications. Neither N/A cam requires computer retuning, and each offers great idle manners. The Stage 2 NSR does require a looser torque converter and also a minimum of 3.73 gears. The Stage 1 NSR blower cam is designed for out-of-the-box boost levels, while Stage 2 is for higher boost output, a looser torque converter, and steeper gears.

The second family of Three-Valve cams is called VSR (Valve Springs Required). If you hadn't guessed it, the VSR cams are much more aggressive than the NSR cams. We've tested VSR cams several times in MM&FF over the years, with great success. Our testing has shown as much as 40hp gains over the stock cars, on stock engines. As with the NSR group, there are two naturally aspirated grinds and two blower stages. The VSR camshafts carry the same description as above but feature a rougher idle and definitely need custom computer tuning.

The third and final family of cams for the triple-valve mod motor are the SPR camshafts, which we tested in the Stage 3 version in this story. Six versions of the camshafts exist on the shelf at Comp. The SPR line is divided into three naturally aspirated grinds and three blower grinds, all broken down into Stage 1, Stage 2, and Stage 3. The first two stages are mild enough to be used with stock engines. Stage 1 can be used on a completely stock engine, while Stage 2 has a rougher idle and calls for taller gears and a better torque converter. Stage 3 is designed for built engines with better flowing heads, more compression, and high boost (in blower applications).

Comp Cams' Web site (www.compcams.com) has more information on each cam and its specific applications. Be sure to check it out to see which XFI camshaft is right for your Three-Valve engine.