'95 to '96 ECU/OBD/Horsepower Changes

From and article on Edmund's:

"Compliance with the U.S. government's emissions regulations for 1996 meant a new engine control computer for the Miata. Amid the recalibration, Mazda found another five horsepower in the 1.8-liter engine for a total of 133."

So anyway, anybody know exactly where they got the 5 horsepower? Are the ECU (electronic/engine control unit) and OBD (on board diagnostics) systems inegrated/embedded in the same part? Will all the OBDI sensors work for the OBDII?

I think I understand that if you want to go FI (forced induction) the five horsepower is not an issue and the OBDI is better to avoid the emissions police. But if you're not doing FI can you retrofit a '96 OBDII and/or '96 ECU to a '94/'95 and get 5 horsepower?

Because OBDII has more sensors, they could tune the computer to tighter tolerences, which, in theory, was worth a few extra ponies. In reality, it turned out to be a wash, and overall, the 96 was no faster. It's not any different than advancing/retarding the timing and/or the cams. You gain one place and lose another. Bottom line, it's not worth messing with!