Future lean burn engine swap into 7th generation Civic sedan? CRX HF, HX?

[mpg_numbers_guy]

Found a 1991 Honda CRX HF for sale for $800. Needs some bodywork and has a few issues (fuel leak, left rear tire, master cylinder). And are those the famous wheels off the lean burn civics?? Honestly if I had spare cash and more mechanical know-how () I would probably buy this thing myself and turn it into a 60+ MPG fuel sipper.

I had looked around a bit for CRX HFs out of curiosity before buying my '04 Civic EX but found next to nothing. Of the two I did find, one looked like it had been towed away from a junkyard, and the other had almost 300K miles--decent condition albeit--but the seller was still asking close to $6K for it.

Out of curiosity, would it be possible to (in the future, if I decide not to sell my Civic later on) swap out a lean burn engine from a CRX HF or even the previous generation Civic into an '04? Or would it be too complicated and expensive?

(Here's the link to the CRX HF if anyone's interested since I won't be benefiting from it: https://www.facebook.com/marketplace...61025957979589)

[oil pan 4]

You don't have to swap the motor if you want to run lean burn.

[hamsterpower]

Is it possible? yes. But you can not drive it on the road. To be road legal in the US the engine must be the same year or newer than the chassis. It would be preferable to swap a modern engine into the older light weight CRX.

Judging by the clear corner lights and hood-pins I seriously doubt that HF still has an HF motor. These were sought after for engine swaps to higher output engines.

[oil pan 4]

Oh I forgot about that.
I will have to start with a 8.1L block instead of a 7.4L block if I want to build an engine for my firebird. Darn.

[19bonestock88]

I wouldn't recommend swapping the older engine into your car, but maybe swapping to a manual transmission... Do some research and find a compatible trans with the highest(numerically lowest) final drive ratio... However getting that CRX as a project could yield some good

[mpg_numbers_guy]

Would swapping in a used '04 HX coupe motor work in the '04 EX sedan? Planning ahead for future reference...in another 100K miles I'll have to change the timing belt again, and maybe by then it'd be more worth it to put in a used HX motor from a same generation Civic with only 40K or so miles on it.

And yes, if it still had the HF motor inside it does seem like a nice project car, but as aforesaid, cash and no mechanical know how limit me. One can always dream though!

[Ecky]

I can't say for certain, but I imagine the '04 HX motor would bolt up to the '04 sedan's transmission, and have mounts in the same place. Part of why the HX gets great mileage is because it has a much taller transmission though.

The HX has a wideband O2 sensor, so you'll have to do a bit of custom wiring there. Most of the rest of the harness will probably be the same.

[elhigh]

"To be road legal in the US the engine must be the same year or newer than the chassis."

You sure about that? Is that nationwide?

<looks online>

In fact it is:

https://www.epa.gov/sites/production...ngswitch_0.pdf

Second paragraph, second page. Spells it out in such a way that includes engine swaps. However an exemption is offered, in that a swap is permissable if it can be demonstrated (or reasonably assumed, according to the text) that a swap will not make emissions worse as "described in Memo 1A," whatever Memo 1A is. No link. But if you do a swap and run it through someone's exhaust analyzer and whistle up better numbers than stock, that might suffice to win you a pass on an older-into-newer swap.

[Ecky]

As for putting an older motor into the newer car, the HF's engine probably doesn't have the power to push your Civic down the road, with the same gearing the HF had, since your car is so much bigger. It may even be less efficient, since it's a non-VTEC motor without coil packs. It was really the whole packaging of the HF that made it an efficient vehicle.

[mpg_numbers_guy]

Originally Posted by Ecky

I can't say for certain, but I imagine the '04 HX motor would bolt up to the '04 sedan's transmission, and have mounts in the same place. Part of why the HX gets great mileage is because it has a much taller transmission though.

Are you saying the taller transmission is more responsible for the increased MPG than the learn burn engine itself?

Originally Posted by Ecky

The HX has a wideband O2 sensor, so you'll have to do a bit of custom wiring there. Most of the rest of the harness will probably be the same.

If I had the mechanical know how (I am waayyy too limited in that area ) I would do it. Or try. If I were able to do it myself an HX engine swap would be around the same $ as having someone replace my overdue timing belt. I would have to convert my car to manual too.

Originally Posted by Ecky

As for putting an older motor into the newer car, the HF's engine probably doesn't have the power to push your Civic down the road, with the same gearing the HF had, since your car is so much bigger. It may even be less efficient, since it's a non-VTEC motor without coil packs. It was really the whole packaging of the HF that made it an efficient vehicle.

Makes sense, including it being illegal. Plus the mounts probably being totally different. Still like the idea of installing a same gen HX engine though, if only.