Off came the stock crank pulley...
Off came the stock crank pulley and damper to facilitate removal of the front cover.
Before we get to the result of the cam swap, it is important to mention the fact that not only did we install the Comp cams, but we also degreed both the stock and aftermarket cams prior to removal and installation. After establishing the baseline power numbers, we installed the degree wheel assembly on loan from Accufab to see how well the factory set up our engine.
As it turned out, the stock cams were way off. Checking the intake centerline (centerline of the intake cab lobe in relation to TDC) first required establishing TDC. This was performed using the piston stop method where a custom piston stop was inserted into the spark plug hole to physically stop the piston at a predetermined point. We then rotated the motor slowly in each direction until the piston hit the stop. Using the two numbers indicated on the degree wheel at each stopped position, we added them together and divided by two to get the precise TDC position. From there, we employed the .050 method to locate the lobe centerlines of both the intake and exhaust cams on each bank. Look for full details on this procedure as well as back-to-back tests on the results of correcting the cam phasing in a future issue. All you need to know now is that the right and left intake lobes were as much as seven degrees different. The exhaust lobes were a little better at just three degrees, but we couldn't help wondering how much power is lost due to the stock cams being so far out of whack?
Due to the cost, complexity and time-consuming nature of the swap, not many four-valve Cobra cam swaps have made it to the dyno for proper verification. Since the cam swap requires removal of the front cover and most of the head gear, many four-valve enthusiasts (and tuners) combine the cams with a head swap, an intake swap or some other modification. While this makes sense from an installation standpoint, it doesn't provide the accurate data required to determine the effectiveness of just the cams.
Once we had the front cover...
Once we had the front cover off, the chain drive system was very similar to the two-valve GT engine.
Knowing this, we elected to install just cams on our motor with no other changes. Also knowing that our reader would want as much information as possible, we elected to go the situation not one but two steps better. To properly demonstrate the worth of the cam swap, we elected to demonstrate the power gains offered in normally aspirated trim as well as with both the Eaton supercharger and the Kenne Bell supercharger. That's right fellow four-valvers, we ran back-to-back tests with the stock and Comp cams with the '01 NA Cobra intake, the Eaton supercharger, and the twin-screw Kenne Bell supercharger. Who else goes to this much trouble for their readers?
The reason for so much testing was that the XE262AH cams were originally designed for a normally aspirated combination, but we suspected that the performance cam profiles would have a positive effect on the power output of our supercharged motor, as well. The only way to determine the effect on both combinations was to run the motor with the stock cams in both normally aspirated and supercharged configuration with the stock cams and then perform the same operation after installing the Comp cams. The Kenne Bell supercharger was added to the mix because we suspected that the Eaton supercharger was nearing its flow limit. We couldn't help but wonder if the flow-limited Eaton supercharger might limit the effective power gains offered by the cam swap.
To determine this, we ran the 4.6 with stock cams with the Kenne Bell supercharger, as well before installing the Comp cams. If the Eaton supercharger did limit the power gains offered by the Comp cams, it would show up as additional power on the Kenne Bell combination. Performing this three-tiered performance test would also allow us to illustrate the difference in power gains between the normally aspirated and supercharged combinations. Basically speaking, is the cam better suited to the normally aspirated or supercharged motor?
Before removing the stock...
Before removing the stock cams, we decided to degree them to check the lobe centerlines. Rumor had it that the left and right bank cams can be dramatically different so we wanted to check for ourselves. We employed this piston stop and degree wheel to establish an exact TDC.
The first step was to run the 4.6 with the '01 NA Cobra intake, the Eaton supercharger, and then the Kenne Bell supercharger. 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 to 13.0:1 and 28 degrees of timing. In normally aspirated trim, the low-compression four-valve motor produced 369 hp at 6,000 rpm and 377 lb-ft of torque at 4,900 rpm.
We then installed the Eaton M112 supercharger with a 7.5-inch crank pulley and a stock blower pulley (9.3 psi). The Eaton supercharger was run with the Accufab inlet and throttle body and produced 532 hp at 6,600 rpm and 480 lb-ft of torque. Next came the Kenne Bell supercharger, also equipped with an Accufab throttle body and a 7.5-inch crank and 4-inch blower pulley (10 psi). The Kenne Bell combination peaked at 594 hp at 6,600 rpm and 493 lb-ft at 4,900 rpm. With our baseline tests out of the way, we tore into the Cobra motor to perform the cam(s) swap.
After installing the Comp grinds, 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. What effect would this have on the power output was anyone's guess, but we will be looking into this in the very near future.
The degree wheel was installed...
The degree wheel was installed along with a dial indicator to indicate the lobe centerline (maximum lift point) relative to TDC.
By marking the crank position...
By marking the crank position .050 before and after maximum lift on the cam, we can determine the exact lobe centerline. Adding the two crank-degree figures (.050 before and after) and dividing by two will give you the centerline.
Here is where the four-valve...
Here is where the four-valve 4.6 differs from its two-valve counterparts. The four-valve motors featured a secondary sprocket and chain assembly designed to drive the intake cam off the exhaust cam.
Removing the tension was a...
Removing the tension was a simple matter of depressing the plunger and inserting a pin to lock the plunger in place.
After removing the rocker...
After removing the rocker arms, we unbolted and removed the cam towers.
Next came removing and replacing...
Next came removing and replacing the factory cams with the Comp XE262AH versions. Make sure to liberally coat the new cams with assembly lube. This is very important as pre-lubing the Modular motor is difficult without some type of pressurized external oiling system.
After replacing the cam towers,...
After replacing the cam towers, we had to compress and install all the hydraulic lifters and rockers using this spring compressor on loan from Accufab.
Here is our newly cammed 4.6...
Here is our newly cammed 4.6 just about ready to go back on the dyno. Awaiting only the valve covers, the cammer motor was already sporting the NA '01 intake.
On the dyno, the low-compression...
On the dyno, the low-compression four-valve 4.6 responded very well to the new Xtreme RPM cam profiles. The peak power jumped from 369 hp to 426, while the torque was up to 390 lb-ft.