Forced Induction And Compression Test - The Multiplier Effect

The final test was to install the ATI blower and intercooler on the high-compression motor. Running the same pulley setup (46-tooth and 73-tooth), the peak power jumped from 543 hp at 7,100 rpm to an amazing 1,350 hp at 7,400 rpm. The torque was equally impressive, as the elevated compression made itself known by pushing the torque curve past 1,000 lb-ft (peaking at 1,020 lb-ft at 6,700 rpm). Once again, the formula suggested a peak number of 1,466 hp (2.70 times 543), but the drive losses cost more than 100 hp at this rpm and boost level. Remember, the difference between the two normally aspirated motors was 65 hp. Adding the supercharger to the mix upped the power difference to a whopping 215 hp. Like the normally aspirated versions, the added compression upped the power output-not just at the power peaks, but also throughout the tested rev range. When you combine the results of this test with those generated by the 2V 4.6L GT motor, it's pretty safe to say the changes in the power output of a normally aspirated motor are actually multiplied when you add boost to the equation. These tests illustrate why we are so adamant about the fact that the best route to a solid forced induction motor is to start with a stout normally aspirated version. As added incentive, any gains you achieve on your normally aspirated motor (by adding ported heads, aftermarket cams, or a free-flowing intake) will actually be multiplied after you install the supercharger.

Effect of Compression (8.3:1 vs. 11.8:1) Normally Aspirated 5.4L 4V.

As expected, increasing the static compression ratio by 3.5 points had a noticeable effect on the power curve. Given that additional compression is always present, power gains were recognized throughout the rev range. The low-compression 5.4L produced 478 hp and 395 lb-ft of torque, while the 11.8:1 version upped the peak numbers to 543 hp and 439 lb-ft of torque. Note that the relative shapes of the power curves remained the same and the additional compression ratio simply elevated the entire torque curve.

Effect of Compression (8.0:1 vs. 12.0:1) Supercharged 5.4L 4V.

Run on the low-compression motor, the ProCharger F2M supercharged upped the peak power to 1,135 hp and 882 lb-ft of torque. This supercharged 5.4L 4V race motor was certainly impressive, but not nearly as impressive as the high-compression version. The ATI blower jumped the power peak of the high-compression motor to a whopping 1,350 hp, while the peak torque now stood at 1,020 lb-ft. If there is any question about whether compression ratio affects normally aspirated and supercharged motors, these graphs should quickly put them to rest. The gains offered in supercharged form were much greater than those achieved normally aspirated. Boost pressure is a multiplier effect, essentially increasing the gains achieved normally aspirated. Remember, this 5.4L 4V was destined for a drag-race vehicle running a steady diet of C16 (high-octane) race fuel. Attempting to combine a high static compression ratio and elevated boost levels is a dangerous affair on pump gas. When fuel octane isn't limited, however, the power gains can be fairly impressive.