Thinking of Civic DX to HX Conversion (lean burn engine)

[vskid3]

I have a 1997 Civic DX sedan that will get around 40MPG at 70MPH with the only modification being 44PSI in the tires. I really wanted to get an HX, but there weren't any available when I was buying a car. I've been thinking of swapping an HX engine into my car, but I would really like to get my current engine over 300k miles (it has 227k now).
Today I found out that the only real difference between the DX engine (D16Y7) and HX engine (D16Y5) is the head, computer, and a wideband O2 sensor. This would allow me to keep most of the original engine and lower costs and time. What I want to do is confirm that all I need is the head and ECU and that there shouldn't any snags that I'll run into. I don't plan on doing the actual conversion for a while, but it will give me a chance to keep my eyes open for parts or a parts car.
How much of a cruising mileage increase should I expect to see? Lean burn will throw off the mileage that my Ultragauge reports, correct? Should I be able to at least tell when it's in lean burn?

[brucepick]

The EPA for the '97 HX is 31 city, 39 highway. Would probably be the same for all the '96-2000 generation HXs but I'm only guessing. You can look up the EPA for your DX and compare. I like cars.com for that but check the EPA site too: EPA

Not sure how the Ultragauge calculates fuel use. If it runs off the OBDII connector and so reads air flow, then yes - lean burn would make it a poor tool for reading mpg. An MPGuino works well though. See the "Instrumentation" forum, and within that, the "OpenGauge / MPGuino FE computer" sub-forum.

With everything you'd need to do to convert the DX to an HX, I don't know if it would be worth the cost and effort. You might need a full HX wiring harness, I don't know. Besides, if there's one oddball sensor that's different, or a change in vacuum hose routing or whatever, you may never find out about it and never get it running right.

Unless your current DX head is already shot. If you need to pull the head anyway, that changes the math. Might be worthwhile if you don't mind sinking in the time + money.

I started with a ScanGauge which tries to read fuel usage from air flow data. I STILL use it intensively to get the car into lean burn and keep it there. I have the procedure to set up an optional custom gauge the SG-II to indicate lean burn but I don't know if the Ultragauge will do that. The throttle position display on SG-II is helpful in getting into lean burn, on the HX. I also usually have the coolant temp and voltage guages showing.

[hamsterpower]

Sorry the HX has vtec-e. That means it has at least one extra wire in the harness. This is partly why they are SO hard to find. The HX model is (or was) VERY desirable at both ends of the spectrum, economy and performance. On the performance side it is a plug and play with the SI (very sporty b16a) swap. All though that may mean you can find the parts you need, less the harness, rather cheap. I still don't believe you will get enough improvement to make back what you will spend. If you still want to go through with this, you could splice in the extra needed wire(s) into your harness.
If you spend much of your time at 70 mph look into aero first for a better return.

[vskid3]

Hm, I think you guys are right about it all being in the details. Using a parts car would probably be the best way to go, so I could just switch everything that is different.

The new EPA ratings for my car are 28 city, 35 hwy, compared to the 31/39 for the HX. The difference is even bigger with the old ratings, with the DX at 32/38 and the HX 37/44. The city mileage of the HX, especially the old rating, is what intrigues me the most. With a couple aero mods I could easily hit 45MPG hwy with the current engine, but city mileage takes technique to improve, and most of the techniques are difficult to do in anything above light traffic. I'm assuming that lean burn wasn't even used on the city portion of the EPA test, which means all the gains are from the way the intake valves operate at low RPMs (one opens all the way while the other opens just a bit to create a swirl effect, VTEC makes them both open all the way at higher RPMs).

So in theory, if I had one intake cam lobe for each cylinder ground down to the same specs as the HX's barely opened valve, my city mileage would be similar to an HX's, correct? I would lose some of the high RPM power, but I never need to go much higher than 3000 RPM. Could the stock computer still control it and take advantage of the increased efficiency? It wouldn't give me lean burn, but it should increase my overall mileage.

[vskid3]

Any thoughts about how having one intake valve open all the way and the other open only a bit would affect economy and power? Would it at least be worth trying?

[California98Civic]

Originally Posted by vskid3

With a couple aero mods I could easily hit 45MPG hwy with the current engine, but city mileage takes technique to improve

I am new to posting on this forum, after lurking some weeks. I drive a 1998 Civic DX Coupe and have for years monitored by milage measuring without a guage, tank to tank. I agree completely that the hypermiling techniques for city driving require reasonably light traffic to work well. I began modifying the car recently, creating a simple WAI, taking 100lbs out in stuff, spare tire, and rear seats, and over-inflating the tires by 4psi (to 48psi). Those mods, combined with seriously devoted hypermiling, yielded 44-46 MPG combined hwy/city on my commute, which I drove before and after the "test" using the exact same route, the same techniques, same time of day in basically the same weather (though, again, I have no mileage guage). I think you can get more out of your DX than you might currently think. Though, I guess, it would take driving like grandpa (like me!).

[brucepick]

Originally Posted by California98Civic

... I agree completely that the hypermiling techniques for city driving require reasonably light traffic to work well...

Excellent! on the mods to the car, and to the "nut behind the wheel". Those are generally the most challenging ones!

Anyway, I've found at in traffic, my mpg can actually go up if I really take advantage of the situation. If you have a standard tranny, that is. Kill the engine and coast at every opportunity, and there will be many. Often you won't have to come to a complete stop, so bump starting it will save wear + tear on the battery and starter. If you do need the starter, not to worry, it takes very little effort to start fully warmed up small engines like ours.

By the way, I've found bump-starting is best in 4th or 5th gear, regardless of speed - just a quick up-down on the clutch to spin the engine a bit, and it will catch fully, AFTER you put the clutch down again. Once it's running again, put it in whatever gear is appropriate. A voltmeter is a good idea, because if your lights or fan etc. are running but the alternator is not (engine off coast), you can lose battery voltage.

[California98Civic]

Thanks for the tip on bump-starting. I have shut the engine off on good long mild hills, but I stopped because I was concerned about starter wear. Any expectation that bump-starting wears on the drivetrain much?

[brucepick]

Originally Posted by California98Civic

... Any expectation that bump-starting wears on the drivetrain much?

Not being an automotive engineer - I can't say. How's that for straightforward?

Anyway, I'm confident that bump starting has about zero wear on the engine. In fact any time spent in EOC should have less wear than if the engine was idling or coasting in gear.

As for wear on the clutch - My guess is the small clutch "event" in spinning up a warm engine is far less wear than your typical moderate start from a stop. In normal use you're getting an entire car to move, in bump starting you're only imparting enough energy to rotate a few pounds of engine parts.

So far as I know, we haven't heard any tales here of people needing a new clutch due to lots of EOC and bump starting. I would hope that if someone on this board or another fuel economy message board had that experience, they would have mentioned it.

[vskid3]

Originally Posted by California98Civic

I am new to posting on this forum, after lurking some weeks. I drive a 1998 Civic DX Coupe and have for years monitored by milage measuring without a guage, tank to tank. I agree completely that the hypermiling techniques for city driving require reasonably light traffic to work well. I began modifying the car recently, creating a simple WAI, taking 100lbs out in stuff, spare tire, and rear seats, and over-inflating the tires by 4psi (to 48psi). Those mods, combined with seriously devoted hypermiling, yielded 44-46 MPG combined hwy/city on my commute, which I drove before and after the "test" using the exact same route, the same techniques, same time of day in basically the same weather (though, again, I have no mileage guage). I think you can get more out of your DX than you might currently think. Though, I guess, it would take driving like grandpa (like me!).

How did you make your WAI? I read that someone on here just removed the air tube from the lid of the filter box (or that's what it sounded like, at least), but I couldn't get mine to come out and I don't want to break it in case it doesn't help.

Unfortunately, most of my city driving is done in an area with steep hills and/or a stop sign every couple hundred yards. For the areas with close stop signs I usually accelerate to about 15MPH fairly quickly and then engine on coast to the sign. Killing the engine wouldn't be worth the hassle, as there is rarely anyone to wait for at the sign so I only have to be stopped long enough for it to legally be considered a stop. The hills are too steep to coast down in neutral without breaking speed records, so I get DFCO most of the way down (confirmed by turning the key to off and there being no difference), offset by 2nd gear climbs to the top. Any tips for driving up steep hills with 20-25MPH speed limits? It seems like no matter what I do, I'm lucky to get 20MPG instant.

There isn't really any weight reduction I could do. I have nowhere to put my tools besides in my car, but they only weigh about 30lbs. The back seat is usually being used by passengers, removing it would just lower my people moving efficiency. I have the radiator fan disabled (the thermostat that controls it needs replaced), so that probably helps a bit vs having it shorted to be on all the time. The only time the coolant temp rises above 203F is prolonged extremely slow driving like looking for a place to park in an extremely crowded parking lot.

I pretty much just try to make up for my less than ideal city driving conditions when I drive on the freeway, in most conditions I can easily exceed 40MPG instant on my Ultragauge. My goal is to keep my fuel costs under $.10 a mile, so as gas prices rise I may have to start adding some areo mods.