1990 civic std hb -> hf
 

I have an old 1990 civic hatchback that unfortunately is on its last cylinder after almost 20 years of service and 270k miles. A while ago I needed a new transmission at one point and my mechanic gave it a 5 speed.. no clue where it came from.. but aside from that it's been pretty much the same car my parents bought me..

I use it as a commuter car.. work is only 10 miles of mostly by uninterrupted freeway.. I was thinking it'd be kinda cool to switch out its engine for an hf engine and try and get the legendary 50mpg ..

what would that entail? is that an easy thing.. and as it wouldn't cost me more than a couple thousand to do?

Your aerodynamics won't be as good as the crx hf and your car will weigh a bit more so that will hurt a little- especially with city driving.

Price a 90 crx hf engine and tranny at car-part.com. You will also need the crx hf computer and possibly a wiring harness.

Do I have to worry about the mpfi conversion? Or the tranny? I was thinking of just swapping the engine and seeing what happens.. anyone have any experience with this could let me know what to expect?

The hf engine is designed to function most efficiently at low rpms and the hf tranny is geared high so it will keep it there.

I don't think I'd do the hf engine swap unless I did the tranny too. I have had good luck with just the hf tranny swap in terms of my highway driving.

If you do the hf engine/computer, you will need to do the mpfi conversion too because that is what the computer was designed to run.

If you're going to that much trouble, I'd just go with a JDM z1 swap. The hf is something like 65hp vs 92hp with the z1, and probably identical mileage. Like Erik pointed out, you won't actually get 50mpg without the correct transmission and driving mods too.

The D15Z1 was never available in Japan. There may have been functionally equivalent D15B engines, but the 'Z1 was only ever available in north american (in the VX) and european (in the VEi) markets.

The two engines have their own distinct power characteristics... A 'Z1 is much happier bolted to a DX/LX geared transmission than the tall gears from an HF. The HF's 'B6 works nicely bolted to it's proper transmission, but will have serious top speed issues with shorter gears, due to its low rev limit.
Further, installing a 'Z1 will require an OBD-1 conversion on top of the MPFI swap that would be required for the 'B6 swap. The 'Z1 has its lean-burn system with its (expensive) wide-band O2 which has been problematic for some.

So, to recap:
D15B6 - Requires HF transmission, MPFI swap. Should be able to pull it off for under a grand (engine + ECU + trans + MPFI wiring) if you do the install yourself.
D15Z1 - Works with the DX/LX 5-speed you may already have, requires MPFI swap + OBD-1 conversion (really, just add 4 more wires when doing the OBD-1 work), may require more work to maintain than the 'B6. Could also be done for under a grand (engine + ECU + OBD-1 conversion) if you already have a usable transmission. A $300 replacement oxygen sensor could push you out of the one-grand envelope.