Port Volume and CSA

[tpepmeie]

While the 427 is torn down, I wanted to take the opportunity to gather some critical measurements on the induction system. Specifically, the average cross-sectional area and port volumes of the heads and injector housings.

Recall these heads were ported in 2010 by RFD, using 39.5mm inlet valves initially. They flowed 343cfm at .500" lift. The injector housings were ported to match, and showed a minimal flow loss of 8.8 cfm at the same lift, compared to the intake port alone.

Fast forward to 2014, new valve seats and larger valves were fitted--now 41.5mm diameter. Flow increased to nearly 380 cfm @ .500". (normalized for valve area, that's 90cfm per sq. in.). The port throat was blended into the new valve seats, and ended up at 36mm, or 87% of the valve OD.





So using a 100cc burette, I gradually filled the intake ports with fluid to determine port volume.

• primary port - 120cc
• secondary port - 124cc
• total volume - 244cc

Using a total port length of 4.85", the average cross-section of the port is therefore 35.5mm. Way smaller than you might think.

The injector housings have a volume of 240cc, and an average csa of 38.8mm. Note they are siamesed, in a "dog-bone" shape at the plenum, for about 1" down into the housing.

The combined system, therefore, has an average area of 37mm from entry to exit. The resulting airspeed through the system, at 7000 rpm on my 4.130 bore/4in stroke engine is 312 Feet per Second avg. This is important for good ram effect and high cylinder filling. Big huge ports, and slow piston speed do not produce enough intake velocity to fill the cylinders completely after BDC.