definetly #2.
Actually, the cam profile and the exhaust closing has a lot to do with filling the cylinder for the next firing.
I'd go with #3. I would think its the initial pressure on the valve and once it opens the air rushes in
Last edited by Ruckus46gt; 11-02-07 at 10:34 AM.
Piston going down, suction caused by seal of piston ring + oil to cyl wall.
-- 06 GT --2006 Mustang GT Premium M5 Tungsten Gray300 RWHP / 313 RWTQ