The engine I have now is a D15B7 1.5 liter 16 valve SOHC. What will
the mileage difference be between a JDM 1.5 VTEC versus what I have?

http://www.honda-tech.com/zerothread?id=2011708

>From what I read from the link above, it sounds like all you need to
do with this type of engine swap is to bypass the VTEC oil pressure
switch. Is that true or do I need to get a VTEC ECU brain box?

Also, what is OBD1 and OBD2?

And what is the difference between a 1.5 VTEC-E economy and a 1.5
VTEC?