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Chevy Big Block Crate 454 Engine - Import Killer, Part 2

925 hp from 454 ci

Photography by Matthew King,

Flow Results

As you study these charts, notice how much more air the smaller AFR intake runner flows at every lift point compared to the factory head.

The intake-to-exhaust flow ratio of the AFR heads is also much better than the stock heads. For example, at 0.600-inch valve lift, the AFR exhaust ports flow about 77 percent of the intake, compared to 59 percent for the iron head. This means you might be better off using a single-pattern camshaft that opens the exhaust valves later in the combustion process, because the longer the exhaust valve stays closed, the longer time the combustion pressure has to push on the piston to make power.

The charts also reveal the gains in flow from the design of AFR's optional CNC-profiled chamber design, which unshrouds the valves and improves flow by maximizing the efficiency of the valve job and port-throat design, especially at lower valve lifts.

Finally, we've included the flow data AFR cylinder head designer Tony Mamo provided us after he port-matched the two Edelbrock intake manifolds we used in this test, a Performer RPM dual-plane and a Victor Jr. single-plane, and reflowed the 305cc head through each manifold. These are the airflow numbers the engine actually sees when it's running, and it reveals that regardless of how well any cylinder head flows, it's only as good as the manifold that's attached to it.

GM cast-iron 313cc w/radius plate AFR 305cc standard chamber w/radius plate
Lift Intake Exhaust Intake Exhaust
0.200 133 98 152 130
0.300 193 127 224 176
0.400 241 157 284 219
0.500 286 176 334 255
0.600 320 190 367 276
0.700 341 199 368 285
AFR 305cc CNC chamber w/radius plate AFR 305cc CNC w/Performer RPM AFR 305cc CNC w/Victor Jr.
Lift Intake Exhaust Intake only Intake only
0.200 163 135 158 160
0.300 241 192 224 230
0.400 300 237 272 286
0.500 344 268 305 324
0.600 367 284 324 346
0.700 362 298 327 337
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