1. Performance engine preparation Tumble & swirl Tumble = In-cylinder air motion in “4-valve” heads Swirl = In-cylinder air motion in “2-valve” heads

2. Performance engine preparation Tumble & swirl Purpose – More complete combustion at idle & low RPM Improves idle quality, part throttle driveability, & economy More volume & velocity across one side of the valve

3. Performance engine preparation Tumble & swirl Tumble/swirl is induced by port angles, cylinder walls, & heart shaped chambers

4. Performance engine preparation Tumble & swirl Too much swirl... Slows intake velocity Reduces VE Washes rings with fuel

5. Performance engine preparation Tumble & swirl Tumble Breaks up as cylinder compresses Fuel is concentrated near spark plug

6. Performance engine preparation Intake valve opening & piston travel Purpose – To better synchronize intake valve opening with max piston velocity Max velocity - When connecting rod is 90º to crank Pressure is low at max velocity Occurs later for higher rod ratios

7. Performance engine preparation Intake valve opening & piston travel Valve opening speed Other factors As rocker arm ratio increases, so does lift, ‘duration’, & area