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Old 09-07-2012, 11:10 PM   #1 (permalink)
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Join Date: Nov 2008
Location: Cincinnati
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Civic CX/HX - '97 Honda Civic CX/HX
Team Honda
90 day: 63.77 mpg (US)
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1997 Civic CX to HX engine/VX trans swap! 63 MPG @ 62 MPH

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!


Last edited by turbovr41991; 10-15-2012 at 06:00 PM.. Reason: Results
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