We Replaced the stock E7TE heads with these Canfield heads. Given the wide variety of performance heads available for the 5.0, just about any aftermarket head will offer substantial power gains.
While it seems counterintuitive that we can increase power while decreasing boost pressure, a better understanding of what boost pressure actually represents is in order. I know it may come as a surprise to some, but boost pressure is actually nothing more than a measurement of backpressure. Whether it's from a blower or turbo, the boost pressure we see on the boost gauge is nothing more than excess air that is having difficulty making its way into the engine. If we increase the flow of air to the motor by increasing the blower or impeller speed relative to that of the motor, then we see an increase in backpressure. The increase in pressure provides more airflow to the chambers every time an intake valve opens, but it also increases the likelihood of harmful detonation.
What if instead of increasing the impeller or rotor speed, we increased the displacement of the motor? What if we installed better cylinder heads, a wilder cam profile, or both? As you might have guessed, the answer is that the same airflow provided by the blower or turbo supplied to a more efficient motor will result in a drop in boost pressure. But since the engine can process more air, this drop in boost pressure will result in a net increase in power. In a small twist of fate, the flow rate of a supercharger or turbo (or any pump really) is proportional to the pressure it supplies. That is to say, a blower, turbo, or even fuel pump will flow less at 40 psi than at 20 psi. This, of course, assumes we keep the impeller or rotor speed constant.
For this test, we combined the head swap with a cam upgrade. We replaced the stock 5.0 cam with an XE266HR unit from Comp's Xtreme Energy line.
A few examples will work wonders here. The first is a test we ran years ago on a Kenne Bell supercharged 5.0L. It illustrated the gains offered by a wilder cam profile on a 302 equipped with a KB supercharger. The 302 was equipped with a set of AFR 185 heads, a GT-40 lower intake, and a stock 5.0 stick cam. The motor was run first with the stock 5.0 H.O. cam and then again with a Comp XE274HR grind. It's not surprising that the motor made more power with the Xtreme Energy cam, but the side benefit of making the motor more efficient with the aggressive cam timing was a drop in boost pressure of just over 1 psi. This came with no change in the blower pulleys because all we did was change the camshaft. The drop in boost pressure from 8.6 psi to 7.4 psi resulted in a jump in power from 440 hp to just over 480 hp. Imagine that-a jump in power that was accompanied by a decrease in boost pressure. You're probably thinking we should have cranked up the boost again to match the original 8.6 psi, but that wasn't part of the test. In our last example with the turbo motor, the turbo self compensates for the artificial drop in boost pressure.
Tested On the dyno, the head and cam upgrade increased the power output by nearly 50 hp. This additional power came with a drop in boost pressure of 1.6 psi.
The second test was run on another 302 motor equipped with a set of stock E7TE heads, a stock 5.0 H.O. cam, and a Holley/Weiand 174 supercharger. Just as with the test run on the KB-supercharged 302, this test with the Weiand blower combined a drop in boost with an increase in power. This test paired a cam and head swap together to offer some serious power gains on the supercharged 302. The carbureted motor was first run with a set of stock E7TE 5.0 iron heads and a stock 5.0 cam. After running the supercharged combination, off came the stock components, and on went a set of Canfield heads and an XE266HR cam. The Xtreme Energy grind was one step below the cam run with the Kenne Bell blower, but it offered a significant step up in performance over the factory grind. Improving the heads and cam increased the power output of the motor by nearly 50 hp while simultaneously dropping boost by 1.6 psi. The new cam and heads improved the motor's ability to process air (increased its efficiency), which decreased the amount of backpressure in the intake manifold. The net result was a drop in boost with an increase in power.