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keepinitsimple 08-03-2014 08:08 PM

Me and my '97 Civic HX
Hi everyone, this thread is to log my modifications, progress, and anything else I do to improve the mpg of the vehicle.

So lets start off with the basic's:

Car: 1997 Honda Civic HX 5-speed manual (California spec, 5 wire 02, all original, and unmodified)
Mileage: 208,506 (as of 8/3/14)

I've been averaging about 31-35 mpg (A/C on about 80% of the time). After doing some searching around the EM forum and Google for any information I can, I figured I should be averaging much higher. So with that said, I will be giving the car a tune up and tweaking a few things.

So far I have done the following things:
1) removed factory rear spoiler (covered the holes with red duct tape)
2) changed ECU from L22 computer (California spec) to A22 computer (49 state spec)
3) increased tire pressure to 42psi
4) Scanguage II and Scangauge E for instrumentation

Things I plan on doing:
1) Clean EGR chamber and valve
2) Full tune up (plugs, oil, fluids, and etc.)
3) Upper and lower grill block
4) Power steering delete
5) Install '92 Civic CX transmission for longer gearing (I have the transmission already and confirmed it to be a CX with code "J8B" on the sticker, and have done the 9 o'clock clutch rotation test to double check)
6) Belly pans
7) Maybe some suspension modifications to lower the vehicle slightly

Driving Notes: I noticed that it is much easier to get the car into lean burn in 5th gear at driving speeds of 65-70 on the highway. I have been finding it difficult to get the car into lean burn in 4th gear when driving around areas with 40-45 mph limits, so I have been doing some P&G driving in the lower gears.

Hopefully we get some more cold fronts that stop by Texas to help cool down the temps a little so I can go outside and work on the car some more.

My goals with the car is to have an aesthetically pleasing and comfortable vehicle that can achieve 50-60+ mpg. I will be tracking any expenses and costs that will go into the vehicle also. Doesn't hurt to save money and save gas and have a little fun doing mods. Hopefully the end result will get me there.

MPGomatic 08-04-2014 07:18 AM

Clean Ride!

So cool to see an unmolested HX ...

EGR and Fuel System clean work wonders. You should see a nice bump.

Are you running synthetic oil and LRR tires?

A/C takes a huge hit on Slambo's (my '99 HX) numbers. Thankfully, it's been mild here in Jersey this summer, and I've been able to run A/C off for the most part. (I haven't done any documented A/C on/off tests yet.)

I've come up with an upper grill block that's wicked easy/clean. Waiting for cooler weather before bolting it in. I tried one lower grill block experiment while it was cooler.

I'm keen on lowering. :thumbup: ... as long as you have good roads ...

Slambo rolled off Craigslist and into my driveway with cheap-o eBay lowering springs and a front strut brace. The suspension's a bit stiff, but handles remarkably well. The rear tires are positive cambered (top in). If all goes as planned, I plan to swap in a real set of springs, along with new shocks and other components.

keepinitsimple 09-18-2014 01:44 AM

Thanks for the comments MPGomatic!

I am currently using Castrol GTX 5W-30 conventional oil. I figured if I switched to full synthetic it may blow by the seals since the vehicle has such high mileage. As for the fuel system, I may have to do that too. A new fuel filter, fuel pump sock, and cleaned injectors will be added to my "To Do" list. As for tires, I do not have LRR tires.

One month progress update:

I did a recent tune up changing spark plugs, oil, and oil filter. When I pulled the spark plugs I noticed they were not the same plugs that were recommended by the Honda HX user manual. The plugs that were in the car were actually NGK ZFR5F-11's. So I swapped them out with the correct ones, NGK V-Power ZFR4F-11's which the HX calls for. Was there a difference? YES!!!

I noticed the car engaged into lean burn MUCH easier in 4th and 5th gears. Idle rpm is much better and slightly lower by 100-150 given rpm's (idle was originally around 790-850 rpm according to the Scangauge, with water temp @ 185F). My mpg went up to 37 to 40 mpg's on a given tank, that is with air conditioning on (toggled off during uphill climbs and accelerating from stops) and tire pressure at 42 psi.

I will probably do the EGR chamber clean up soon and see if that makes any additional difference (ordered new egr chamber gasket and egr valve gasket from Majestic Honda earlier today). My upper grill block is in the making and will be put on soon since the weather temps are starting to cool down a bit here in Texas. I should be able to run the car with the AC off more often now.

I've also consider maybe adding some hood hinge spacers and longer bolts to see if it will help the air flow transition from the hood/windshield while reducing under the hood engine temps (an idea taken from the Honda drag racing world that my buddy mentioned to me). I figured it would be worth a shot instead of removing the wipers or modifying the hood itself. I should be able to watch where the rain droplets flow over the windshield while driving confirming if it works maybe?

As for the lower grill block, I have a spare bumper that I may use as a template to make a block that will accommodate for fog lights and adjustability of air flow to the radiator via ducting and an additional puller fan.

As for the CX transmission I picked up, I've cleaned it up, resurfaced the CX flywheel, and is ready to be installed once my new clutch gets here. I'll weigh the HX and CX flywheels to see if there is a difference.

I have also done other normal maintenance such as full brake fluid flush, clutch fluid flush, power steering fluid flush. Still needs a coolant flush and transmission flush, but I will have the CX transmission in with fresh fluid.

Minimal gains so far, but any progress is better than no progress! :cool:

Baltothewolf 09-18-2014 01:56 AM

Do NOT put that CX tranny in your car unless you don't want L/B anymore. When I put the CX tranny into my HX my ability to go into L/B was severely limited. The problem is you have to be above 2400 RPM to be in L/B. I tested this going to work multiple times. I used to be able to cruise at 65mph and be in L/B. When I put the CX tranny in I had to be at 70+ just to get into L/B. Just saying.

keepinitsimple 09-18-2014 02:07 AM

Balto, thanks for the heads up. My car currently gets into lean burn at 65 mph and 2400 rpm in 5th gear just as you mentioned and is fairly easy to maintain. Were you able to still engage LB in 4th gear with the CX transmission? I figured with the longer gearing, target LB rpm can still be obtained cruising in 4th gear instead of 5th gear?

Also, do you think could switching to 13" wheels might help hit the target rpm range in the higher gears?

Baltothewolf 09-18-2014 02:18 AM


Originally Posted by keepinitsimple (Post 446060)
Balto, thanks for the heads up. My car currently gets into lean burn at 65 mph and 2400 rpm in 5th gear just as you mentioned and is fairly easy to maintain. Were you able to still engage LB in 4th gear with the CX transmission? I figured with the longer gearing, target LB rpm can still be obtained cruising in 4th gear instead of 5th gear?

Also, do you think could switching to 13" wheels might help hit the target rpm range in the higher gears?

Yea but the mpg gain from the CX tranny didn't outweigh the loss of having to run in a lower gear. As for the smaller tires, wouldn't that be foolish? You would be adding 12% Taller gears then reducing it back to the way it was with smaller tires. I would recommend driving it like you are now. I'm not sure what RPM you shift at, but when I went from shifting at 2250 to shifting at 2750-3k I gained 3mpg. I can get into L/B Insight as low as 1300rpm.

Shift from first to second at 3-3.2k.
Shift from second to third at 2750-3k.
Third to fourth at 2500.
Fourth to fifth at 2250. Maybe 2500 if merging on the freeway.

[Edit]: If you plan on doing serious aero mods, like underbelly panel, boat tail, grill block, lower height, LRR tires, mirror delete, etc etc then the taller gears would probably be of benefit due to being able to travel at higher speeds with lower engine load. You would be able to do 70mph and get great mpg, and still be in L/B.

Chrysler kid 09-20-2014 01:05 PM

Hey another hx in dfw! Do you have a factory radio?

I have a JDM d15b trans with shorter gearing and I have been getting better mileage than my last hx (with the factory trans) in the city for sure. The gearing difference is not noticeable enough to justify switching unless your old trans is getting crunchy. As mentioned nearly all gears are the same except final drive but if you have it go for it. My car tends to "bog" under 2000 rpms and at highway I want to be at peak efficiency for acceleration and coasting which seems to be at 2400 for my vehicle at least. As mentioned above lower rpms can mean little because the engine needs to make more power and it would not be in its power curve to efficiently accelerate without lots of air and fuel. My shift points are also as mentioned above and the throttle is much more crisp and response at those levels

I dig the front lip it is a civic vti or si front lip, I went cheap with the Mugen style. I'd like to scoop up some used eibach lowering springs eventually

What kind of shape is your exhaust manifold in? If its original your cat may not be as efficient as it use to be with that mileage and the manifolds known cracking issues. My car has an aftermarket intake :( I can't find a stock one anywhere however the radiator fan blows hot air directly into the aftermarket intake which has been having a positive effect on my gas mileage. The intake has also made the pedal feel more responsive. The factory intake is routed to pull cold air in from outside the engine bay which is good for power but not gas mileage

My factory cat was replaced around 220k with the amazon unit and previous owner did mentioned it did improve his gas mileage slightly

My car was on its original plugs with a deteriorated gap oF twice what spec is. You should definitely now do the wires and cap and rotor they look original.

The egr valve cleaning is absolutely necessary. At 294k my passages on the intake were completely clogged, and my valve was stuck shut until I completely dis assembled it and got it working again. Just get a ton of brake cleaner like 3 cans, and clean out the passage on the intake manifold and the feeder passage coming into the egr, and the egr itself. I should mention even online the egr for these cars are still $150, though I do believe an egr valve from the 1998 accord will interchange but I have yet to test that

For the hood hinge you should not need it. Even with my ac on this summer my temperatures barely tip half way on the needle and the fan kicks on only when I've been stopped at a light for a few minutes. You'll be able to block the grille without any ill effects, you should also be able to run a medium sized block in the middle of the bumper behind the license plate. You can try it out and report us back on if it helps aero, but it's basically going to be sucking air out of the engine bay disturbing air flow over the windshield.

I am able to see 34mpg city without much effort. If you are due for tires do not cheap out, get low rolling resistance tires. It really helped my numbers. Get yourself a full tune up and you will be hitting 38mpg with mixed city and highway driving. When I was running the Walmart Douglas tires the best I could get was 36mpg all highway miles, now on my low resistance tires I can get that without using my ac in the city and turning the car off and gliding to a stop light. If I'm lucky I can decelerate enough to just pop the clutch into 3rd gear to restat the car and keep on driving

RPM 11-30-2014 08:06 PM

Hi, nice car keepinitsimple!

Can someone please explain to me how the lean burn works on the HX?

I have a lean burn EK Civic (EK3), and the ECONO (i.e. lean burn) light comes on from barely above idle to 2500 rpm in 3rd and 4th and 3000 rpm in 5th. In 1st and 2nd, lean burn is not available.

I am interested to learn about the differences between my car and this HX you got in the US.

Chrysler kid 12-01-2014 08:33 AM

Lean burn is only available in 5th gear for the hx.

Our hx is a 1.6 motor
coupe only
wheels are light weight enkei designed wheels
5 pin wideband oxygen sensor
no moonroof
power windows and power locks standard
no cruise control
California models primarily did not have lean burn as it produces higher emissions
only civic from 92-00 to have an egr valve
cylinder head is designed to spin inward air into the combustion chamber
exhaust valve springs have a harder spring ratrate
Cam is slightly more agressive than ex model

The most telling sign a car is a hx is power windowindows with no sunroof. All ex trim models came with a moon roof, and all base models came without power windows

As far as lean burn it is the computer relying the car to restrict fuel above a cetrain speed and throttle point

RPM 12-01-2014 08:42 AM

Thanks Chrysler kid. Very interesting that lean burn is only available in 5th gear. Do you know what the rev range is?

These differences between the Japanese/European and the American models may have to do with differences in the emissions regulations as well.

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