Opening the inlet valve | |
Earlier | Later |
More power at higher rpm | Less power |
More overlap with exhaust valve | More torque at lower rpm |
Lower flexibility | Better emissions! |
Poorer response at low rpm |
Closing the inlet valve | |
Earlier | Later |
Less power | More power at higher rpm |
Higher compression ratio at low rpm | Compression ratio improves with higher rpm |
Better torque | max. torque in higher rpm band |
More flexible engine |
Opening the exhaust valve | |
Earlier | Later |
Less pumping losses, bit more power | More pumping losses,less power |
Hotter outlet valve | More complete combustion, less emissions |
More chance of pre-ignition | Lower exhaust temperature! |
Closing the exhaust valve | |
Earlier | Later |
Less overlap with inlet valve | Part of intake mixture goes straight into exhaust at lower rpm (engine is "Off cam") |
More flexible engine at low rpm | More high end power |
Less power at higher rpm | Less flexible engine at low rpm |
More torque at low rpm | Low torque at lower rpm |
Improved emissions |