Another test where larger valve hurt air flow.

When conducting a development program on a new head, we will “basically” destroy the port to find out what helps and hurts performance.

Part of this testing is to determine what size valves will produce the best air flow.

Most of the time, especially in heads designed to produce less than 400 horsepower, machining the seats and installing a larger valve hurts air flow.

Here is another case in point: .

Engine Quest Cast Iron Small Block Mopar Magnum Cylinder Head.

Lift                 1.925       2.02

.100                 66             63

.200                 149           138

.300                 198            185

.400                 232           225

.500                 246           253

.600                 255           257

While there was a 7 cfm gain at .500” lift and 2 cfm at .600”, the 2.02 valve reduced air flow 9 cfm and 13 cfm at .200” and .300” lift respectively.

If you find a person with flow bench experience on a particular head, go with him vs. someone who is guessing.

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