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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
Ran my port to valve area numbers again.

Port cross section:
32mm port is apx 1.23 sq inch area
40mm port is apx 1.96 sq inch area

Area under valve seat:

49mm valve has about 6.1" of circumference.

6.1" x .455" lift for an SC cam = 3.21 sq inch.

6.1" x .378" lift for a 930 cam would = 2.31 sq inch.

Compare port volume to area under valve seat:
2.78-3.21 sq in....area at full lift for 930 to SC cam verses,
1.23-1.95 sq in....area for 32-40mm intake ports.

Put an SC cam with a stock 930 port volume and there is way more lift than is need with 3.21 sq in. area volume under the intake valve seat at full lift for a port that can only flow 1.23 sq in of volume.

This would make the area under the valve 260% larger than the port.

Kind of cool info and not what I expected. I thought lift equaled more air flow.

It dose some but because of the increased lobe ramp angle, not because of the higher gross lift.

These numbers are nominal. The area under the valve might be less depending on diameter at the seat, the ports might be more or less than there published numbers, and the lift might be less depending on how the cam was measured.

Fun stuff!

Last edited by 911st; 01-28-2010 at 03:55 PM..
Old 01-28-2010, 03:53 PM
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