Richard Holdener
December 16, 2009

Part 2
In Part 1 of our Fast Ford Formula, we demonstrated the effectiveness of replacing the stock 5.0L components with aftermarket bolt-ons on our 347 stroker motor supplied by Demon Engines. Equipped with factory E7TE heads, 5.0L cam and GT-40 intake, the 347 produced 307 hp at 4,700 rpm and 401 lb-ft of torque at 3,300 rpm. Once we installed the XFI stroker cam, RHS 200cc aluminum heads and Edelbrock RPM II intake, peak power jumped to 448 hp at 6,200 rpm and 420 lb-ft of torque at 5,200 rpm.

The simple bolt-ons resulted in gains of 141 hp and 19 lb-ft of torque, though the horsepower gains were as much as 200 hp past the power peak. There was only a slight drop in low-rpm power (up to 4,000 rpm), but the huge gains higher in the rev range more than offset the slight losses down low.

After swapping the blower pulley from the Novi 1220 to the Vortech, we were back in business. Loading the 347 under boost at 3,300 rpm resulted in torque figures exceeding 450 lb-ft. Running 27 degrees of total timing and an air/fuel ratio of 12.2:1, we were rewarded with peak numbers of 421 hp at 5,500 rpm and 462 lb-ft of torque at 4,200 rpm. The boost curve increased from a low of 2.4 psi at 3,300 rpm to 8 psi at 5,700 rpm. Even at 3,300 rpm, the blower improved torque production of the 347 from 401 lb-ft to 461 lb-ft.

The question was whether these bolt-on upgrades would show an even larger gain once we added boost. Our plan was to run a Paxton centrifugal supercharger on both configurations to illustrate the gains offered under boost. Given the significant increase offered in normally aspirated trim, we were anxious to see how well the Demon stroker performed with the blower.

The guys from Paxton came to the rescue with their 5.0L Mustang kit, which includes the Novi 1220 SL supercharger. The Novi featured internal oiling for self-lubrication, which meant installation of the blower kit did not require drilling and tapping (or welding) the drain pan for an oil drain back. This also meant we were not required to provide an oil-feed line. We chose the Novi 1220 for its ease of installation (and testing) and for its ideal sizing for our low-boost and power needs.

Calculations prior to testing told us the 300hp 347 might produce over 400 hp once we added 7 psi of boost from our Novi. Once we added the RHS heads, Xtreme Energy cam, and Holley Systemax II intake, the normally aspirated power output would easily exceed 400 hp, meaning the boosted motor would likely exceed 600 hp! Obviously, we needed a supercharger that was not only capable of supporting this outright power level, but one that would be equally efficient at the lower power level produced with the stock components. The Novi 1220 seemed to fit the bill nicely, as it was capable of supporting well over 750 hp, while still maintaining the efficiency at lower power levels.

To illustrate the gains offered not only by the supercharger, but by the combination of supercharger and bolt-ons, we configured the 347 test motor first with the stock heads, cam and GT-40 intake. In this configuration, the 347 produced 307 hp and 401 lb-ft of torque in normally aspirated trim. The Novi supercharger was installed and run with a 3.80-inch blower pulley and 6.75-inch crank pulley.

This drive ratio combined with the internal step ratio of 3.45:1 to produce a peak impeller speed of 36,769 rpm at a peak engine speed of 6,000 rpm (though this was well past the power peak). This impeller speed eventually produced a peak boost reading of 8 psi at 5,700 rpm (as high as we revved the stock combination). Running race fuel on the supercharged combination allowed us to get a tad more aggressive on the air/fuel ratio and timing curves than we might on the street.

Unfortunately, we were unable to fully utilize the Novi 1220 supercharger as the author made a major mistake while testing. The valve covers used for testing did not feature a baffle to eliminate oil from escaping and we were forced to attach a small shop towel over the breather vent. Though secured to the breather vent with a hose clamp, a portion of the shop towel found its way into the impeller of the Novi 1220-ouch! Luckily, we had a replacement supercharger in the form of a Vortech S-trim. Though the design (and therefore boost and power output) mirrored the Novi 1220, the downside was that it was not self-lubricating and therefore required us to provide a feed line and drill and tap the oil pan for the oil return. Let that be a lesson that hopefully you won't have to learn the hard way.

Photo Gallery

View Photo Gallery

Photo Gallery

View Photo Gallery

Note that the rising boost curve offered by the centrifugal design increased the speed where the motor made peak torque. Where the normally aspirated combination produced peak power at 4,700 rpm and peak torque at 3,300 rpm, the supercharger upped these values to 5,500 rpm and 4,200 rpm. It seems obvious that an efficient blower like the Novi 1220 (or Vortech S-trim) is an ideal way to improve the power output of stock 5.0L, even one equipped with a Demon stroker short-block.

Once we were satisfied with the results of adding the Paxton/Vortech supercharger to the stock configuration, it was time to add boost to the bolt-ons. Off came the stock heads, cam and GT-40 intake and on went the RHS aluminum heads, Comp XFI hydraulic roller cam and Edelbrock RPM II EFI intake. Ever present was the Accufab throttle body and matching EGR spacer.

To keep things consistent, no changes were made to the drive pulleys (either crank or blower). This would help illustrate any changes to the boost curve brought about by the bolt-ons. The FAST XFI management system made quick work of tuning the 36-pound injectors and we were eventually rewarded with peak power numbers of 665 hp at 6,300 rpm and 559 lb-ft of torque at 5,500 rpm. In hindsight, we should have run something larger than the 36-lb/hr injectors, as even with 65 psi of static fuel pressure (but no boost reference), we were well and truly out of fuel. The power curve was still climbing rapidly, but we shut off the fun at 6,300 rpm due to the resulting lean mixture.

With sufficient fuel and engine speed, power would easily have eclipsed 700 hp, but for our needs, the peak power was actually irrelevant, as we were looking for differences in power and boost. A comparison of the power output between the stock components and bolt-ons reveal that the bolt-ons were worth 141 hp in normally aspirated trim, but once we added boost to the equation, the gains increased to 244 hp, though additional fuel and engine speed would surely have increased this figure.

Just for fun, let's apply our Power/Boost Formula to this test. As a reminder, the Power/Boost Formula states mathematically that any changes in power in normally aspirated trim are actually multiplied by the boost present. By this we mean than if you take a 300hp motor and add 1 bar (14.7 psi), you should double the power output to 600 hp. If you then increase the power output of that 300hp motor to 400hp (with bolt-ons) and then add the same 14.7 psi of boost, the power output will double to 800 hp. Increasing the power output of the theoretical base engine by 100 hp resulted in an increase of 200 hp once we added the boost.

If we apply this formula to our 307hp motor, we see that adding 8 psi should increase the output by 0.5442 percent (8 psi/14.7[1 bar] = 0.5442) for a total of 474 hp. We obviously did not reach that power level when we applied 8 psi to our 307hp normally aspirated stroker, but there are at least two very important reasons why it failed to do so.

The first is that the formula is not absolute and assumes a 100 percent increase in power based on doubling the atmospheric pressure. Though we sometimes reach or even exceed the suggested power levels with turbos, some of the power from the formula is required to drive the supercharger itself. The parasitic losses associated with driving the supercharger must be subtracted from the total. The second reason is that the combination itself was somewhat self-limiting. Combining the stock heads, cam and (to a lesser extent) GT-40 intake dramatically reduced the ability of the motor to process air. It is true that the blower improved airflow into the motor, but that air must also come out and the mild cam timing and restrictive exhaust ports on the E7TE heads made life difficult to process the additional airflow. So restrictive were the stock components that the bolt-ons increased the power output of the stock configuration more than 8 psi of boost from the supercharger.

Things changed once we improved the power output of the motor with the performance components. Replacing the stock heads, cam and intake with the RHS heads, XFI cam and RPM II intake allowed the supercharger to shine as the modified motor produced 448 hp. According to our formula, adding 8 psi of boost should increase the power output by the same 0.5442 percent, for a total of 692 hp. Our motor produced 665 hp, but this peak number was more a function of our lack of fuel. We suspect that we would be much closer to the number suggested by the formula with our modified motor than with the stock configuration.

What all this boils down to that the best supercharged motors start out as powerful normally aspirated combinations. It sounds simple, but the more powerful the normally aspirated motor, the more powerful your supercharger combination. Not only that, but the gains applied to the normally aspirated combination area actually multiplied by the boost. Thus it is possible to add 100 hp to your normally aspirated motor and have that equate to 200 hp on a turbo or supercharged combination (at 14.7 psi). If you have to choose between boost and bolt-ons, the best choice is always both!

Photo Gallery

View Photo Gallery