Originally Posted by bboy
Yeah the problem with lowering the dynamic compression (VTEC, valve overlap) on a FI car is you just blow your air and fuel out the exhaust valve becuase of the boost.
You can design the two cam profiles to be whatever you want with VTEC. Presumably, the high-boost camshaft would be extremely low valve overlap. IE: late IVO and late IVC, which would give little/no overlap, and very low dynamic compression.
The real problem is pumping losses. You have all that boost trying to push the air into the engine only for the piston to push it back out before the intake valve closes.
All that boost pressure takes a lot of exhaust pressure to generate, thus raising your EGT and increasing cyllinder temperatures.