MBE began experimenting with fully CNC'd intake manifolds while looking at ways to improve its Nextel Cup heads. "In Nextel Cup, they are now pushing 9,700 to 9,800 rpm, and that places a big stress on the head to flow enough air to properly fill the combustion chamber in a very small amount of time," Bieneman says. "There is a reason well-designed cylinder head ports are the size they are. Low-rpm engines need smaller ports to make good low-end torque. High-rpm engines like we see in Nextel Cup racing need big intake ports to allow plenty of air and fuel into the combustion chamber at the upper-rpm range.
"That's when we noticed that it was the intake manifold that was becoming the limiting factor. We reached a point where the intake runners were choking off what the cylinder head was receiving. So we began considering the intake runner as a continuation of the intake port. We began working the runner and port together, creating volumes that worked as well as possible. We looked for an angle of flow from the carburetor to the intake valve that was as direct as we could get. The results were just fantastic; not only did we improve power, but we moved peak power 400 rpm higher. That's almost unheard of."
Once MBE realized the potential that was available from machining cylinder heads and intake manifolds as a package, the company began working to translate what it has learned from its Nextel Cup pieces to how it can help engine packages for traditionally "lower level" racing. Some of the head/manifold combinations required extensive work to optimize, but Bieneman says the results are worth it. For example, in his big-block cylinder head program, Bieneman moved two of the intake port entrances on each head over 0.2 inch. That makes for a lot of aluminum to be cut away, but Bieneman reports that the resulting improvement in the ports produces a significant improvement in both torque and horsepower. Not too bad when engine builders have to fight for a five-horsepower advantage wherever they can find it.
A premium set of CNC-ported cylinder heads is of little use if your out-of-the-box intake manifold is harming the flow of the air/fuel mixture into the combustion chambers.