Advanced Timing The first...
Advanced Timing
The first test involved altering the factory timing curve. From the factory, the '03 Cobra motor featured a pretty conservative ignition timing curve. Down between 3,000-3,500 rpm, Ford equipped the motors with 14-15 degrees of total timing. We have seen even less on the chassis dyno if the temperatures are high. The Ford Racing crate motor was run with the factory timing curve to establish a baseline then again after revising the timing curve to produce 23 degrees of total timing throughout the rev range. The additional timing had a dramatic effect on the power curve. There was very little gain in peak power since the factory curve already featured 23 degrees of timing from 6,000-6,500 rpm. Check out the huge gains (40 lb-ft) down near 3,000 rpm.
While pulley changes are certainly popular, Ford has seen fit to make things somewhat difficult when it comes time to up the boost pressure. The stock Cobra pulleys are pressed onto the supercharger snout shaft, making removal somewhat more difficult than a simple unbolt-and-go procedure. Luckily for us, many aftermarket sources offer removal tools for the stock Cobra pulleys. Ours came from the guys at Kenne Bell and was a first class piece that included detailed instructions, all the necessary hardware and worked flawlessly.
After removing the stock Cobra blower pulley, we installed the new Dial Ur Boost (DUB) pulley system from South Florida Pulley Headquarters. Rather than a single (press on and/or off) blower pulley, the DUB system relied on a press-on hub adapter that allowed easy installation of different blower pulleys. Once the hub adapter was installed, pulley changes required only unbolting the four retaining bolts. This DUB system is perfect for a dual-purpose Cobra where boost can be kept at a reasonable level for the street, but quickly changed at the strip for some quick e.t.'s Like the pulley removal tool from Kenne Bell, the DUB system came with detailed instructions easily understood-even for the first timer.
With the 4.6 now equipped with the Flow Tech exhaust and Accufab throttle body, we swapped out the stock blower pulley for a 3.20-inch DUB pulley. According to the information provided by South Florida, the smaller 3.20 DUB pulley could be run with the stock blower belt. As expected, the 3.20-inch blower pulley increased the peak boost pressure by a hair over 2 psi (from 8.7 to 10.9 psi) and improved the power output significantly. The peak power now checked in at 530 hp, while the torque took a monster leap from 463 lb-ft to 506. As expected of a change in boost pressure, the horsepower gains were consistent throughout the rev range. The roughly parallel horsepower curves meant that the torque gains were more pronounced at lower engine speeds. The horsepower improvements seemed to reach a point of diminishing returns as the engine speed exceeded 6,000 rpm. Perhaps we were nearing the flow limit of the Eaton supercharger, since it was designed to feed a 390hp motor and not something easily exceeding 500 hp. With over 500 lb-ft of torque, this was one impressive 281 cubic-inch street motor and proof positive that it is tough to beat forced induction for making serious power.
When it comes to Cobra owners and boost, more is always better. While this philosophy can sometimes get owners into trouble (spelled D E T O N A T I O N), there is definitely more power to be had by going beyond 10.9 psi of boost. Knowing this, we utilized the DUB system once again and swapped out the 3.20-inch blower pulley for a smaller 2.93-inch pulley. The interchangeable DUB system made installation a snap--it took just a minute or so to perform the swap.
Stock TB vs. Accufab TB (8.5...
Stock TB vs. Accufab TB (8.5 psi)--Ford Racing '03 Cobra Motor
The F.A.S.T. system allowed us to eliminate everything on the inlet system in front of the stock throttle body. Thinking that the stock throttle body and inlet into the blower was a possible restriction, we installed an Accufab throttle body and inlet upgrade. The billet aluminum Accufab pieces upped the power peak to 508 hp, while peak torque increased by 2 lb-ft.
Combining the 2.93-inch blower pulley with the stock blower belt took the stock spring-loaded belt tensioner to the end of its available adjustment. Rather than run to the store for a new blower belt, we moved the alternator on its mount to effectively decrease the belt length. This put the tensioner back in the proper range for maximum belt tension. The 2.93-inch blower pulley upped the peak boost pressure from 10.9 to 13.3 psi. As another sure sign that we were nearing the flow limit of the Eaton supercharger, the peak power leveled off at 538 hp (a gain of just 8 hp), while the peak torque took another huge jump from 506 lb-ft to 550. Notice now that for the first time, the supercharged engine produced more peak torque than horsepower. Though the peak numbers seemed to be limited, the increased boost pressure sure improved the power output throughout the remainder of the curve.
The results of the previous two pulley changes seemed to indicate that we were limited in terms of maximum power potential, but this final test confirmed it. After running the pair of DUB blower pulleys, we decided to change the crank pulley. There is a limit to the available reduction in blower pulley size, as a dramatic reduction will reduce the available surface (belt) contact, the mechanical leverage and belt wrap, all which increase the possibility of supercharger belt slippage. Lucky for us, installing a larger crank pulley has the same effect as reducing the size of the blower pulley. Knowing this, we installed a 7.75-inch crank pulley system from South Florida Pulley Headquarters.
Like the DUB blower pulley system, the 7.75-inch crank pulley system eliminated the factory crank pulley with an adjustable hub that facilitated the installation of different size crank pulleys to increase the boost pressure. The larger crank pulley increased the peak boost pressure from 13.3 to 14.5 psi. The gains were not as impressive as the previous attempts, as the peak power was up by just 1 hp, while the peak torque now stood at 569 lb-ft. The pulley changes didn't seem to be offering anything other than increased low and mid-range torque so, while we had a number of other (larger) crank pulleys at our disposal, we decided to call it a day with our Ford Racing crate motor still in one piece.
Stock TB vs. Accufab TB (8.5...
Stock TB vs. Accufab TB (8.5 psi)--Ford Racing '03 Cobra Motor
The F.A.S.T. system allowed us to eliminate everything on the inlet system in front of the stock throttle body. Thinking that the stock throttle body and inlet into the blower was a possible restriction, we installed an Accufab throttle body and inlet upgrade. The billet aluminum Accufab pieces upped the power peak to 508 hp, while peak torque increased by 2 lb-ft.
Stock TB vs. Accufab TB (12.5...
Stock TB vs. Accufab TB (12.5 psi)--Ford Racing '03 Cobra MotorKnowing that inlet restrictions become more pronounced with increased power levels, we retested the Accufab throttle body and inlet against the stock systems at a higher boost level. Where the Accufab combination increased the power output by 6-7 hp at 8.5 psi, the gains were 11-12 hp at 12.5 psi. The greater the power level of the motor, the more restrictive the stock throttle body becomes.
Stock Blower Pulley vs. DUB...
Stock Blower Pulley vs. DUB 3.20--Ford Racing '03 Cobra Motor
This is the test we were all waiting for. Nothing wakes up a supercharged motor like more boost. Using the Dial Ur Boost (DUB) pulley system from South Florida Pulley Headquarters, we replaced the stock blower pulley with a smaller 3.20-inch version. The pulley change increased the peak boost pressure from 8.7 to 10.9 psi and the peak power output along with it. Equipped with the DUB 3.20 pulley, the Ford Racing crate motor now produced 530 hp and 506 lb-ft of torque.
DUB 3.20 vs. DUB 2.93--Ford...
DUB 3.20 vs. DUB 2.93--Ford Racing '03 Cobra Motor
Following the Cobra owners adage if some boost is good then more must be even better, we replaced the 3.20-inch DUB pulley with a smaller 2.93-inch version. Once again, the pulley change upped the boost pressure from 10.9 to 13.3 psi. The peak horsepower output was up only slightly, from 530 to 538 hp, but the torque peak jumped from 506 to 550 lb-ft.
Stock Crank Pulley vs. 7.75--Ford...
Stock Crank Pulley vs. 7.75--Ford Racing '03 Cobra Motor
Though we knew the Eaton supercharger was now the limiting factor in terms of peak power, we decided to up the boost one step further by installing a larger crank pulley. As expected, the peak boost pressure went up slightly, from 13.3 to 14.5 psi, but the peak power was up just 1 hp. The peak torque was now up to 569 lb-ft, but the additional blower speed was having no effect on the peak power. All we were managing to do was elevate the front half of the power curve. These power gains are obviously welcome, but what this motor really needs is a larger or more efficient supercharger (a situation we will definitely be curing in the very near future).
Boost Curve Stock vs. 3.2...
Boost Curve Stock vs. 3.2 vs. 2.93 vs. 7.75 Crank
This graph illustrates the boost curves provided by the four different pulley combinations, stock, 3.2 blower, 2.93 blower and 7.75 crank. Note the shape of the stock boost curve (lowest on the graph). Note that the boost increased ever so slightly from 3,000 to 5,000 rpm then fell off slightly thereafter. This trend was repeated with the installation of the 3.20 DUB pulley (second from bottom), but things changed once we installed the 2.93 DUB blower pulley (third from bottom). The boost curve remained pretty consistent from 3,400 to 5,100 rpm, then fell off dramatically. The drop off was even more pronounced once we upped the boost pressure with the 7.75-inch crank pulley (top curve). Note the dramatic fall off in boost pressure. The Eaton supercharger has simply run out of flow potential.
To install the new crank pulley...
To install the new crank pulley system, we began by removing the stock Cobra crank pulley. Note the bearing cage used to support the stock blower pulley.
Here is the Metco idler pulley...
Here is the Metco idler pulley installed on the 4.6.
The 7.75-inch crank pulley...
The 7.75-inch crank pulley upped the boost pressure to 14.5 psi, but the peak power was actually down 1 hp. As before, the additional boost pressure improved the torque production, but we were definitely at the flow limit of the Eaton supercharger.