1997 Civic CX to HX engine/VX trans swap! 63 MPG @ 62 MPH

[turbovr41991]

Are you interested in how a HX engine works with a VX transmission???
It nets 63.21 mpg going 62 mph at a steady speed on the highway! If you find this interesting, the by all means, keep reading!

I came to a crossroads with the civic. After looking at my 1997 Civic CX engine leaking oil from the front main and coolant from the water pump, I knew it was it was due for some much needed maintenance. Both were slow leaks, but still need attention. So instead of doing the logical timing belt, front main, and water pump, I am swapping the engine over to the HX instead!

For those that did not know, I picked up a rusty 97 civic HX manual trans car to harvest all its rare HX parts onto my extra clean CX hatchback.

Then the plan is to swap all my CX parts back to the HX shell and will sell it for the same if not more money than what I paid for it, making the net cost of these modifications NOTHING, just my time in labor. End result lean burn engine with a tall geared transmisison in a lighter version of the car without power steering.

Items I wanted off the HX in the CX:

1) HX wheels swap Completed
2) center console swap Completed
3) Power Windows swap In process (20% finished, harness swap harder than expected)
4) Power locks swap In process (20% finished, harness swap harder than expected)
5) D16Y5 Engine, wiring harness, and ECU swap Completed
6) HX cluster swap In process (95% finished everything works except shift light)

The ultimate goal was to have lean burn along with a tall gear VX transmission to have the more options to get optical gas mileage.

After 6 tanks of gas I can say the results are good with room for improvment.

5th gear lean burn seems to be ideal when the engine has only been run for 5-10 minutes. After the engine has first warmed up, I can get in low RPM lean burn and get 63.21 mpg on flat at an average of 62 MPH. This is at 2050 RPM in 5th gear. The car is very picky about when it can allow this low RPM lean burn, but when it does watch out! This past weekend I literally got in, warmed the car up while getting on the highway, got it into low RPM Lean burn, and drove 200 miles without poping out of lean burn mode! At that 200 mile mark I was exiting the highway reaching my destination. Will keep everyone posted on this as I am THRILLED with the results.

4th gear lean burn yields the great MPG. On flat it seems to be 59.73 MPG at 58 mph. This is also with RPM at 2400, throttle at 20, and engine load at 57. This is literally, getting on the highway, and maintaining 2400 RPM in lean burn. No pulse and glide, no EOC, No DFCO, no drafting. Literally going 58 MPH and maintaining that speed and RPM while getting this mile per gallon. Probably just an aero mod away from getting 60mpg.

I have also seen the best hill climb mpg while in 4th gear lean burn. Steep grades and still able to net 43+ mpg. Previously I would be in 5th gear and drop to 33-36 mpg on these grades in 5th gear going the same speed. Another huge improvement!

HX engine has more torque and power than the old CX engine. It is easier to accelerate and maintain speed at lower RPM.

If anyone is planning to do this swap, it was 100% plug and play. Get an HX dropout (with everything), 5 wire (fed spec) manual transmission harness and a Manual transmission ECU.

Only a few slight differences in the swap I want to point out:
1) Throttle cable is completely different. You could make the CX/DX/LX work , but I would recommend getting the stock cable as well as the mounting bracket that bolts to the strut tower.
2) Fuel line return. Probably not large enough of a difference to NEED swapping, but they are slightly different in length. Also swap the bracket that holds it to the intake manifold. (Depending on your needs, Power steering also shares the same bracket and can be separated by drilling out a spot weld on the bracket.)
3) Brake booster hose. Is formed completely different. Will need the HX one.

Thanks for reading!

[turbovr41991]

Anyways, on to the engine swap. After a mere 3 hours or work and the engine and trans are out of the HX.

Hoping to get more time this weekend to work on it. Held up on lead times to getting some new seals and such to freshen up the HX engine before putting it in. Will take some pics along the way!

[02ws6]

All those seals and maintenance things are too easy to get to when the engines are out of these cars.. Make sure to go ahead and freshen up both. Itll be worth it down the road.

Keep rocking the photos!

[96vtec]

Good work! I was planning on doing the same thing when my HX was rear ended but ended up selling it for $900. Didn't want to deal with the trouble of parting out everything else and cutting up the chassis or paying to get the shell junked.

It'd also be a good idea to wash the engine bay while the motor's out. Maybe check for any rust as well.

+1 for more pics and steady progress!

[turbovr41991]

Originally Posted by 02ws6

All those seals and maintenance things are too easy to get to when the engines are out of these cars.. Make sure to go ahead and freshen up both. Itll be worth it down the road.

Thanks. I wound up replacing all the lower seals, water pump, timing belt, and all the valve cover gaskets. I also adjusted the valves too which were probably neglected for a while... The other just got a timing belt, water pump and front main.

Originally Posted by 96vtec

Good work! I was planning on doing the same thing when my HX was rear ended but ended up selling it for $900. Didn't want to deal with the trouble of parting out everything else and cutting up the chassis or paying to get the shell junked.

It'd also be a good idea to wash the engine bay while the motor's out. Maybe check for any rust as well.

+1 for more pics and steady progress!

I think I read your post on wondering what to do. Was it a 95 CX swap you were considering? That would be a much harder swap than this one. These are both OBD2 cars so it plug and play and swapping over the stuff to make it work.

Updated pictures from yesterday. Sorry for the low quality camera phone pictures. Both engines are out, the HX engine has been freshened up. Hoping to have it back together today or tomorrow. Will take better pictures today.

[turbovr41991]

Hands were too dirty today to take pictures and ran out of time. Both engines are "in."

The hatchback (HX swap) needs the clutch bleed, oil, coolant, and to put the hood and tires back on.

Coupe needs a few electrical, fuel, power steering, coolant lines, all the above from the hatchback.

Great progress, but just ran out of time.

[96vtec]

I was actually planning on the same swap, from a 96 HX to a 96-00 CX. I live in the city and there isn't much room for anything...

So what are your plans for the HX coupe? You should swap the doors as well so that you'll have power windows on the hatch.

I can't wait till you're done and get those mpg numbers up.

[turbovr41991]

Originally Posted by 96vtec

So what are your plans for the HX coupe? You should swap the doors as well so that you'll have power windows on the hatch.

Cool. I guess I stumbled upon another potential swap thread.

As for the future of the HX Coupe, I will probabaly sell the to a friend. I don't have much money in it and I have a couple friends who would like a cheap civic to save money on fuel.

I am definately taking the power locks and windows!

[turbovr41991]

I drove the CX with its new engine today. Drove great with no check engine lights or issues! I drove it for about 30 miles and went to the gas station to top off so I can see some improved numbers. I had to reset my scan gauge after the swap because it was not reading mpg after the swap. Now it is fixed, but I have to go through the calibration process again. Probably for the best as I am expecting a decent gain in fuel economy from this!

[02ws6]

The hatch has a hx/vx swap now? Hows the trans?