By Richard Holdener/Photos By Author
Before you think about a cam swap, better make sure you have sufficient spring pressure.
Making more power is a common goal, and the great thing about wanting more power is that there are many ways to go about getting it. Though we applied what we learned to a 5.0L Ford combination, it works equally well on just about every engine family out there, from Ford to Ferrari. Improving the power output of any internal combustion engine is a simple matter of increasing the airflow through the motor. This works because the internal combustion engine is nothing more than a giant air pump. The more air that goes into (actually through) the motor, the more power that comes out. Increasing the amount of air processed by the motor can be achieved through things likes forced induction, increased displacement or (like ours) basic bolt ons. The basic bolt ons include things like cylinder heads, intake manifolds and camshafts. We chose to upgrade the cam on our 5.0L Ford, but before we could successfully perform the cam swap, we needed to upgrade one of the many subsystems, namely the valve springs.
Though a simple giant air pump, every component must work together to maximize the flow through the system. If just one component is not functioning properly, the whole pump suffers. In the case of our 302-based test motor, the valve springs were holding back not only the current power production, but they were limiting future outputs as well. Before we could hope to improve the output of the motor with a cam swap, we had to make the necessary preparations. The test motor originally came as a short block from Blue Print Engines. Supplied as a short block, the BP306sp crate motor produced 306 inches thanks to a .040 over bore. Far from exotic, the 302-based combo featured a cast crank, 5.155-inch rods and flat-top, hypereutectic pistons. The BPE short block also featured a healthy hydraulic roller cam (.543/.554, 218/226 112 lsa), but still needed cylinder heads and an induction system to be complete.
To get the 306 ready for testing, we installed a set of BPE aluminum, as-cast heads, a dual-plane intake and Crane roller rockers. The BPE aluminum 190-cc castings featured a 2.02/1.60 valve package, 60-cc combustion chambers and a valve spring package designed for a hydraulic-roller cam profile. Testing with the supplied cam and a Speedmaster Eliminator intake, we experienced valve float starting before 6,000 rpm. This ultimately limited the available engine speed, and therefore power potential, of the Ford combination. Given that we planned to run a slightly more aggressive cam profile, with even more rpm potential, we first needed to cure the valve float before we could hope to further improve the power output with the cam swap.
Check out the supplied photos and captions for a rundown on the came swap, but we replaced the existing double springs supplied with the BPE heads with a set of 26056-16 beehive springs from COMP Cams. The spring upgrade also included a set of 4696-16 locators and 703-16 steel retainers. The spring upgrade improved both the seat and open pressures, as well as the coil-bind clearance that allowed us to run higher-lift cam profiles. Naturally, the cam swap improved the power output (check out the supplied graph), but it was only possible with the right valve springs.
Graph: Effect of Spring Swap- 306 Ford
Before we could even think about replacing the cam in our 5.0L Ford, we had to address an issue with valve control. The valve springs supplied on our BPE as-cast, aluminum heads were simply not up to the task of controlling the valve much past 6,000 rpm. Before installation of the COMP XE274HR cam, we upgraded the valve springs to allow us to take full advantage of the rpm capability of the wilder cam timing. As evident by the graphs, valve float was in full force at 6,200 rpm with the supplied springs. After installation of the 26056 spring package from COMP Cams, the motor revved cleanly to 6,500 rpm.