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Old 02-02-2009, 01:48 PM   #1 (permalink)
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1986 Honda Civic Hatchback Si - What can I do?

I'm fairly new to ecomodding/hypermiling, so bear with me on this. I used to live right next to my job, and drove a big SUV daily (about 4 miles total) and didn't really care about MPG much. Not long ago, I got a new job about 25 miles away from my home so I bought a small fuel efficient car in my price range (cheap) to drive to work and back every day. What I got is a 1986 Honda Civic Si (hatchback). So far, it gets about 30 MPG and will probably get better once the winter weather here clears a bit (less idling, less churning through snow/ice). What I'm wondering is what can I do to improve the FE of this little buzzbox mechanically? I'm a mechanical engineer and a shadetree mechanic so I'm open to doing just about anything, so long as it isn't very expensive or would require the vehicle to be down for weeks.

So far, the only things I can think of are pretty lame and probably won't do much. I was going to:
1. Switch to the lightest synthetic oil in the engine + transmission recommended
2. Pump up the tires to the maximum allowable pressure on the sidewall (44psi)
3. Remove the passenger side mirror
4. Remove the spare tire , jack, and tools from trunk (it's dry rotted anyway and I wouldn't feel safe driving on it, so if I get a flat it's getting towed or I'll have my wife take me and the tire somewhere to get it patched)
5. Remove some of the emissions equipment and tune up the engine (the idle is a bit rough and the throttle response is choppy - I blame the 800 feet of vacuum lines running between all of the emissions stuff).

Here are some dumb/rediculous things I was thinking about:
1. Replacing the transmission with an HF model from a civic or a CRX. The thing runs about 3600 rpms going down the highway at 75, and honestly has more than enough power at this speed, so why not cut that gear ratio and up the fuel mileage?
2. Replacing the wheels with lighter ones + adding LRR tires. This will probably happen when the current tires wear out.
3. Remove rear seat, "extra" trim, insulation, etc.

Are any of these ideas stupid? I'd rather not waste my time/money doing something that won't make much of a difference in the long run. Where could I get my best bang for the buck/effort? I don't want/need 80 MPG, but a noticable improvement would be nice. I understand that my driving habits are the biggest things to change, but what can I do mechanically to get my mileage up? Thanks for the help all, I'll log my mileage before and after any changes to try and validate the effects and possibly help others looking for good info on how to improve their mileage as well.

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Old 02-02-2009, 01:50 PM   #2 (permalink)
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Hello and welcome to the site. You'll really want to look at our two lists here:

For modifications:
60+ Vehicle modifications for better fuel economy - EcoModder.com

For large gains and a little extra effort on your part:
100+ hypermiling / ecodriving tips to increase gas mileage - EcoModder.com
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Old 02-02-2009, 02:32 PM   #3 (permalink)
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Redbox - '86 Honda Civic Si
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Quote:
Originally Posted by Daox View Post
Hello and welcome to the site. You'll really want to look at our two lists here:

For modifications:
60+ Vehicle modifications for better fuel economy - EcoModder.com

For large gains and a little extra effort on your part:
100+ hypermiling / ecodriving tips to increase gas mileage - EcoModder.com
I've read all of those and can see the value in most of those points, but is there anything that would be particularly helpful in relation to this particular car?

For example: The transmission ratios give it some "pep" but also some pretty short legs on the highway. Does anyone know of an easy swap, or even a gearing change that can be done with junkyard parts? Could I oversize the tires to reduce rpms, or would that bring it's own problems to the table?

The aerodynamics seem pretty bad, but there's not much I can do about that without making it hideous or spending a lot of money.
Would lowering it help (it's pretty low, it would scrape on things if lowered)?
Would blocking the airflow to the engine help (it seems like it's pretty well blocked as-is)? If so, do I block the "grill" vents or the "facia" vents? What about making movable louvers that I could open in hot weather and close in cold weather? Had that been done?
Would a K&N or cold-air type intake help (I have my doubts, the stock intake isn't particularly restrictive)?

I guess I'm just looking for tips tailored to this type of car, and I figure that there is a lot of specific advice for a small 4 cylinder hatchback from the 80's on this site.
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Old 02-03-2009, 02:33 AM   #4 (permalink)
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the 1985-1987 hf tranny will fit, the 1984-1987 dx and base model tranny will fit to and only give you slightly better gearing then you have, but not nearly as high as the HF but you should find out if your engine feels ok running at 1,500-2,000 rpm, just try it, shift in to 5th gear in town.
I would not mess with the vacuum lines other then replace them with new lines, removing them or the emissions equipment on these cars tends to kill mileage, performance and over heat the engine till it dies.
I have a passenger side mirror delete from my '84 civic hatch that I am willing to part with for $5 plus shipping if you can wait till the weather is above freezing.
No one ever changes the pcv valve (under the intake manifold on the other models), or tranny fluid (every other year!), wide tires are commen but a set of 13" rims with 155/80 R13 tires would be best for mileage.
If you need any parts, I have a '84 dx that was rear ended on the drivers side, still has alot of good part, time + shipping, I also have the PDF of the dealer shop manual at my web siteRight Here check it out.
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Old 02-03-2009, 07:40 AM   #5 (permalink)
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Quote:
Originally Posted by Ryland View Post
the 1985-1987 hf tranny will fit, the 1984-1987 dx and base model tranny will fit to and only give you slightly better gearing then you have, but not nearly as high as the HF but you should find out if your engine feels ok running at 1,500-2,000 rpm, just try it, shift in to 5th gear in town.
I would not mess with the vacuum lines other then replace them with new lines, removing them or the emissions equipment on these cars tends to kill mileage, performance and over heat the engine till it dies.
I have a passenger side mirror delete from my '84 civic hatch that I am willing to part with for $5 plus shipping if you can wait till the weather is above freezing.
No one ever changes the pcv valve (under the intake manifold on the other models), or tranny fluid (every other year!), wide tires are commen but a set of 13" rims with 155/80 R13 tires would be best for mileage.
If you need any parts, I have a '84 dx that was rear ended on the drivers side, still has alot of good part, time + shipping, I also have the PDF of the dealer shop manual at my web siteRight Here check it out.
It's still got the stock rims in suprisingly good condition, with some newer Hancook cheap-o tires installed. Once they wear out, I'll probably try to get some lighter alloys in the same size and run the tire size you recommend.

Excellent information, thanks. I'll take the mirror delete, just PM me the payment details whenever you get a chance to remove it.

Do you know much about jumpy idle problems in these cars? When I bought it, the idle was all kinds of erratic. I cleaned out the throttle body and intake manifold with carb cleaner (without removing the throttle body) which helped a LOT, but I've heard that to truly cure a jumpy idle you need to remove and seriously clean the idle air control valve. Do you have any experience with this?

One part I can think of from the 84 DX that I definately need is the shift linkage, if it would fit correctly (4 speed vs. 5 speed?). The front bushings on mine are shot, but they're rivetted into the clevis joint and seem to be non-replacable. I'm going to try and replace the rivet with a long bolt to "tighten" up the bushings and reduce play, but that will only last so long until the linkage becomes 100% unusable. What kind of shape is yours in? Also, you wouldn't happen to have any leads on rear speaker panels for a 84-87 hatchback model would you?

Also, if you can remove the dome light cover without breaking the tabs off (easier said than done apparently), I'll take it too. The previous owner must have preferred to remove trim pieces with a jackhammer.
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Old 08-15-2009, 02:09 AM   #6 (permalink)
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Hi, I realize this thread is a little old but actually just acquired an 87 Civic Si myself. You can get the rubber bushing for your transmission shift linkage from hondaautomotiveparts.com- Yep thats right, original factory parts! and they don't even cost that much! The "clevis joint" you so called described is held in by a thing called a spring clip, basically a pin you have to drive out of the shaft and the linkage pops right off you have to slide back the rubber boot back to see it which I belive has a clamp on it to hold it in place. By the way you would find this out if you picked up a repair manual, which you need for torque specs anyway ........... you are a mechanical engineer right??? I would not put any kind of tranny fluid into the transmission except Honda Manual Transmission Fluid. Also in the realm of your world ......mechanical engineer..... those gears and and that fluid is design for each other. That tranny fluid is designed to meet the force generated by that fluid, and that transmission is designed to operate within the limits of the oil. Maybe you have had better luck than I have but I have tried all different types of fluids (synthetics included) and have not found a single one that makes the transmission shift like the factory fluid does. The repair manual states that if you are not able to get the factory fluid that you can use 10w-40? temporarily until you are able to use the factory fluid. If you are having jump throttle problems you might want to check the computer which is under the passenger side seat, again in the repair book. No check engine light? Maybe someone removed the bulb or you have other issues going on, the computer should still tell you whats going on. If you need a new throttle body you can get one from hondaautomotiveparts.com or one from your local salvage U-Pull-It, some of the sensors or built into the throttle body and cannot be replaced, just might be an O2 sensor causing the problem as well. The HF tranny swap was a great idea! I loved it! But what might really boost your mileage is a swap to a 1.3L, it could be substantial! Check out this website 3g Fuel Injection Swap - Red Pepper Racing . Might have to figure out or find some smaller fuel injectors though. That sounds like it is about as far as you can go from the factory. I plan on stepping it up a notch with mine......Propane power kits, propane conversion, small engine propane conversion kits, auto propane conversions - 3-4 Cylinder LPG Conversion Kit when I get the $850 of course. Once I convert it over it will be a gasoline/propane hybrid and I will be able to switch it to run on either one or the other at the flip of a switch, but here's the nifty trick I keep reading about, you can use that set up to run the car off of a fuel cell, or in other words a hydrogen car! Virtually no pollution! unless your car burns oil. This dude is working on it or has basically the same set up I want to put together for his dodge truck Water for Fuel . However, with propane, I have heard that since the fuel is a dry fuel (just like hydrogen is) and is not wet like gas or diesel, I heard that it can eat up piston rings. It makes sense, but often times things that make sense are not always true. So I really don't know. The only thing with propane kits is I read somewhere if you convert it over to propane it is supposed to be certified by the EPA. If you don't want to go crazy like I am (but virtually use no gas!) you could try a hydroxybooster like the one on this site http://smacksboosters.110mb.com/GenI_links.html . The guy used to have free plans on his site but I can't seem to find them, maybe the video is still up. Well have fun and be safe!

Last edited by SiGuy; 08-15-2009 at 02:42 AM..
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Old 08-15-2009, 02:39 AM   #7 (permalink)
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Found injectors that might work for the 1.3L swap: 2003 HONDA CIVIC HYBRID 1.3L 1339cc L4 ELECTRIC/GAS FI [LDA1] : Fuel/Air : Fuel Injector. If you go to RockAuto.com you can see a pic. You might have to get a wire harness from a wrecking yard so that you can clip the plug-ins off to solder them to your existing wire harness. Remanufactured injectors are $36.89 on the web site.
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Old 08-15-2009, 12:52 PM   #8 (permalink)
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Found the website for the smack booster http://www.smacksboosters.110mb.com/Smack.pdf. Hope all the info I have helps!
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Old 08-15-2009, 02:31 PM   #9 (permalink)
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Old 08-18-2009, 12:09 PM   #10 (permalink)
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SiGuy - Don't waste your time and money with a "smack booster". There is nothing free in life. Thanks for the honda automotive parts website, there is some useful stuff on there, however the shift components I needed are not there.

Honda Automotive Parts

The portion I've been looking for is number 14 here, and I only need the bushings for the front clevis on that part. That site (and most others) don't even list 14 as being available, and the junkyards I consulted either had nothing or overpriced worn out units, so I just pulled the thing apart and put plastic spacers from Lowes in there to fill the gap (I "machined" them with my bench grinder and a handheld drill). It's been going strong for about 8 months now but I know I'll have to redo it sooner or later. However the fix cost about $6 and took about 2 hours to complete total, so I can do it every 6 months until the car is shot and not be too put out, especially since the car will probably be shot in about 6 months.

Does anyone have a good way to "repair" rusted out floorpans? The original owner opted for or was forced to buy rustproofing, and wherever the rustproofing goo was applied is now fully rusted out. Hilariously, the parts with just the factory paint are almost like new. It looks like the rustproofer did a fine job of holding moisture against the metal it was adhered to. Anyway, the floor pans are pretty much shot but the actual "frame" of the unibody is pretty good. I was just going to rivet some old stop signs or something in there for now, does anyone have a good tip or trick on how to keep from accidentally going fred flintstone some day?

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