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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
Just some of my calculations so they are in one place:

Port cross section:
32mm port is apx 1.23 sq inch area
35mm port is apx 1.50 sq inch area (930 exhaust)
38mm port is apx 1.77 sq inch area
40mm port is apx 1.96 sq inch area

Area under valve seat:

49mm intake valve has about a 6.1" of circumference.
41.5mm exhaust valve has about a 5.15 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.

Intake:
32mm ports require .2 lift for area under the valve seat to equal the port area.
38mm ports require .29 lift for area under the valve seat to equal the port area.
40mm ports require . 32 lift for area under the valve seat to equal the port area.

Exhaust:
35mm ports require .29 lift for area under the valve seat.

49mm
41.5mm

118% larger circumference.

If 35mm exhaust port is 1.77 in sq, and the intake is 118% larger, a 38mm intake matches.

993tt ports:
43mm = 2.27 sq in. (28% larger)
38mm = 1.77 sq in
Old 02-01-2010, 02:03 PM
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