Will the D16Y5 or the D17A6 (both are HX engines) bolt in the EF(4G) Civic as simple as the D16Z6(5G Si engine) does?I hear the D17A6 may req. additional sensor input 'cuz of the ECU.

 

It should fit assuming you attach all the old EF engine mounts and tranny to the new engine. Wiring would be a big of a nightmare if you wanted to use an HX OBD II ECU (the VTEC-E OBD I engine was in a VX hatchback). You might be able to use a VX OBD I computer with an HX engine and using an pre-OBD to OBD I conversion harness. I guess that brings up the question of why. VTEC-E is neat for gas milage but isn't really a performance design and the simpler D16Z6 SOHC VTEC swap would be easier and faster for probably the same money, maybe less since it's an EG/older engine.