Intake Manifold
1994-98 5.9L Dodge Cummins


Why is the CFM+ the ultimate intake manifold? Regardless of which tuner, air filter, exhaust system or aftermarket intake you may already have, you need to dramatically increase your air flow. No other aftermarket intake comes close. Even without a computer its easy to see why the CFM+ (CFM Plus) flows so much better than the angular stock aluminum manifold with its nearly 40% flow restriction at the front mounting bolts.

But why does the CFM+ (CFM Plus) flow so much more air than the other oversized cast aluminum manifolds in the market and maintain lower air temps?

1.) The very large center section of the competitor cast aluminum manifold may look impressive but it is very bad for flow. The inlet to the manifold from the intercooler and the outlet of the intake manifold into the engine are very similar in cross-sectional area so when the center section is over three times larger than the inlet and outlet the air flow slows dramatically through this center section. The air flow then is forced to speed up to exit. This causes turbulence in the flow, leading to pressure drop or pumping losses. 2.) The competitors manifold is so oversized in the center section that two of the mounting fasteners which hold the intake to the engine had to be changed to long bolts or studs that must pass directly through the air flow. This causes tremendous turbulence in the flow leading to additional pressure drop or pumping losses.

3.) You can also see in the picture of the cross-section of the competitor aluminum manifold there are two surfaces protruding down into the flow path that create recesses into the outside surface of the manifold. These pockets allow the mounting nuts to look good recessed on the outside but cause a big problem on the inside where it matters. These two surfaces protruding into the air flow act to trip up or tumble the air flow. Again this causes additional turbulence in the flow leading to pressure drop or pumping losses.

4.) Cast aluminum has a much rougher surface than the advanced technology composite CFM+ manifold. The rough interior surface of the competitors cast aluminum manifold causes additional turbulence. 

5.) The volume of air that can get stuffed into the engine is also greatly affected by the density of the air flow. If the manifold's material acts to insulate the hot under the hood air from reheating the air flow that has just come out of the intercooler that is a very good thing for maintaining air density but if the material readily conducts heat (such as aluminum) that would cause the inlet temperatures to raise.