Cam for L92 Heads: Lessons Learned
Overlap can bleed off cylinder pressure (not compression) due to reversion at lower engine speeds. Anything that hampers cylinder filling will alter cylinder pressure.
Now, when the engine is in tune and harmonics in the intake and exhaust start working together, overlap will add cylinder pressure from increased cylinder filling.
KCS is right though that the only way you can alter dynamic compression is with a later IVC event, but it can be misleading. Later IVC event will bleed off cylinder pressure at lower engine speeds just like added overlap will, but just like overlap aiding in cylinder filling when the engine is in tune, a later IVC event will increase trapped air mass at higher engine speeds adding cylinder pressure.
Now, when the engine is in tune and harmonics in the intake and exhaust start working together, overlap will add cylinder pressure from increased cylinder filling.
KCS is right though that the only way you can alter dynamic compression is with a later IVC event, but it can be misleading. Later IVC event will bleed off cylinder pressure at lower engine speeds just like added overlap will, but just like overlap aiding in cylinder filling when the engine is in tune, a later IVC event will increase trapped air mass at higher engine speeds adding cylinder pressure.
