It is true that with a SOHC VTEC, you only have the VTEC affect on the intake side of the cam (there is only so much room on a camshaft for lobes) however, and I know I'm going to get crap for this one, so what. VTEC has much less of an effect on outgoing air than it does on incoming.

If your refering to a D16Z6 vs B16A, your comparing two entirely different engines. All B-series VTEC's have more aggressive cam shafts, higher compression and more aggressive fuel and timing maps to make that extra power. If you'd like, look up the hp rating of a DOHC ZC and SOHC ZC, I believe their both rated at 130hp. Seeya.