Michael Galimi
February 18, 2011

"Experience with different combos and testing numerous size cylinder heads on a variety of applications is priceless. We can hypothesize all we want, but real-world testing is the only true test," noted Burcham, who also discussed the bigger isn't always better cliché. "If you put a 225cc intake runner on a 306ci, then the engine would seriously lack bottom-end and mid-range horsepower and torque. It would, however, scream at 8,000 rpm (given the proper valvetrain and intake manifold). But if a 306ci engine with the same 225cc intake runner had some sort of forced induction, then the port size would have a less negative effect on the bottom-end and mid-range results.

Neugent agreed about the lazy low-end with large cylinder heads on a small engine, and went on to tell us about the opposite side of the equation. "The same goes for an engine that has large cubic inches and small cylinder heads. The engine would have tons of torque but run out of power on the top-end. You can only pump so much air through a small head. It would be the same as trying to pour five gallons of water into a one-gallon bucket." That was exactly what was happening with our test engine‚the intake runners were too small given its 331ci size and the supercharger huffing in more air.

The Brodix 195cc heads use a 2.02-inch intake valve and the 210cc features a 2.08-inch valve; both heads rely on a 1.60-inch exhaust valve. Burcham chose the Brodix LH 210cc heads, which come fully CNC-ported by noted engine-builder Keith Craft. Brodix lists the heads as KC-LH-F 210cc, noting the style of head and its CNC port job. He selected the heads for the large intake runners and significant flow numbers over the un-ported, baseline 170cc heads that had just come off the test engine.

A cylinder head's airflow is also critical when selecting heads for your engine, and there is a relationship to the intake port volume. Burcham explained, "The intake and exhaust port sizing is important for port velocity, which is based on the runner's size. A smaller cc port that flows 300 cfm will normally help the engine make more horsepower than a port that is, for example, 10cc bigger and flows the same 300 cfm." Burcham told us that the higher air speeds and velocity fill the cylinder better, which allows the engine to accelerate quicker and ultimately make more power.

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The Brodix LH 210cc heads we sampled flowed 298 cfm at 0.500-inch lift and 317 cfm at 0.600-inch lift on the intake side. We didn't flow the ports at higher lift ranges as our application features a mild hydraulic camshaft that checks in at 0.560/0.570-inch lift. Those results are 2 cfm less than the flow numbers shown on Brodix's website. The difference is probably due to variations between the flowbenches.

Moving to the exhaust, our independent testing showed the exhaust ports flowing 217 cfm at 0.500-inch and 221 at 0.600-inch lift. Typically, as the bore size increases, so does the cfm flow as it unshrouds the valves by moving the cylinder wall away from them. We didn't test a set of LH 195cc heads, but Brodix touts them as moving 287 and 294 cfm at 0.500- and 0.600-inch, respectively. The exhaust ports in the 195cc version flow less due to less porting-209 and 213 cfm at the two big lift numbers of 0.500- and 0.600-inch.

"Pay attention to the flow numbers in the mid- and low-lift areas when selecting a cylinder head. Too often people focus on the peak number, which is usually at 0.700-inch lift. That result doesn't matter when your cam has a max of 0.500-inch. The mid- and low-lift results are more important-during combustion a valve travels past the 0.100, 0.200, 0.300, and 0.400 ranges twice and only hits the peak once," notes Burcham.

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