Help! 92 civic cx d15z1 swap

[Onedopehatch]

So I bought this 92 civic cx from a buddy of mine for a daily driver. The motor and Trans had been swapped by the guy before my buddy. It gets around 35mpg combined (city/highway) and when I first got it I thought it was great gas then I started to look and it seems that the z1 should be getting well over 40 mpgs, so I started digging and looking through car more closely and found that it's running of a p05 but shouldn't it be operating off of a p07? Vtec isn't hooked up because It doesn't have a vtec ecu doesn't it mean it doesn't lean burn as well to save gas? Would swapping to a p07 fix the gas issue? I'm Nee to the whole ecomodding thing. I've done all of the maintenance on it and tire pressure and such. Any help is welcome, thanks