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 Bowen follows up with a bowl...  Bowen follows up with a bowl cutter to ensure the transition into the first angle is smooth. Care must be taken here though, Bowen warns. Opening up the bowl too much can cause low-lift flow to suffer.  Rather than progressive angles,...  Rather than progressive angles, the exhaust gets a much simpler profile with a 45-degree valve seat followed by a radius to allow the pressurized exhaust gas to exit quickly.  In finished form, it's difficult...  In finished form, it's difficult to see the minute angles, but the small amount of material removed will make all the difference for airflow.  If you look closely you can...  If you look closely you can spot the back-cut on the foremost intake valve. Thirty degrees is good for most street engines since it improves low-lift flow, but some racers opt for slightly different angles since the back-cut can affect the flow at each level of valve lift.  Undercutting involves reducing...  Undercutting involves reducing the diameter of the valve stem in an attempt to lessen the intrusion the air has to flow around. Bowen says it's more hype than help in most cases, and he typically doesn't undercut the valves unless asked by the customer.  Back on the flow bench, peak...  Back on the flow bench, peak intake flow rose to 253 cfm at .600-inch lift and 203 cfm at .700-inch lift on the exhaust. There are a lot of variables to consider, including differences in engine combinations and cylinder head design, but Bowen says he's seen similar flow increases net an easy 20-30 hp on relatively mild naturally aspirated small-blocks.
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