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Old 02-08-2011, 10:43 PM   #1 (permalink)
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FlatBlackHatch - '91 Honda Civic Hatchback Standard
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91 Civic Hatchback Std. 4spd Manual "aka" Newbie

Hello all,
I have been looking at your site for a few weeks now and love some of the great ideas for hypermiling. I've always been a gas miser, usually because I accelerate slow and go the speed limit. I got my 1991 Civic Hatchback Standard 4 speed manual 1.5 liter about 1-1/2 years ago and have seen as high as 42mpg for a tank, but average around 40mpg or recently lower. According to the 2008 ratings of 30 combined, I guess I'm doing pretty good. I would just like to see how far I can push it.

It looks like there are lots of civics on here, but I don't know if my particular one is on here. Luckily it's the same year as SVOboy, just a different model. I have a few questions I have been pondering lately and would like any feedback ya'll (note the southern accent) have.

1. I am wondering how close the CRX is to mine. Since we can't use a scanguage, I'm driving blind. I also wonder since I have a 4 speed, what is the most fuel efficient constant speed? My speedometer has a small 55 making me think this indicates the best speed, but with only 4 gears I wondered if the best speed was slower (45? or even something like 30 in 4th gear?). I am asking this to anyone with an mpguino or supermid that can figure this out. This would at least let me know they best speed to go. I have a feeling that going 60 or 55 on the highway isn't great for my FE as the RPM's would be high. By the way, my car doesn't come with a tach either, so I just used the gear ratios and online calculators to figure out rpm's.

2. Are you typically accelerating slowly (like 1/3 throttle) and shifting before 2,000 (I don't have a tachometer, but I think that would correlate to shifting at 10, 20, and 30 mph for me). For pulse and gliding, do you use a faster or higher rpm? I saw a post of SVOboy's that says its not good to p&g over 35 mph, so is it best for me to just pick a speed and hold the throttle? Then maybe just try to coast whenever it makes sense? I don't feel comfortable shutting off the engine yet (have had problems starting), but neutral coasting seems ok to me.

3. By doing this 2,000 rpm "short-shifting" is there anything bad it could do to my car? I started to hear some knocking the other day (I am about to check if the manual transmission fluid is low, just changed my oil filter and filled up oil). At the moment it seems if I go back to the owner's manual recommended shift points of 15, 25, & 40, the sound tends to go away. I also noticed for all the other 91 civic's it showed in the manual, they gave a "cruise" acceleration around 10, 20, 30 (this equates to 2,000rpm's)....but for mine they only gave the "normal" shift points, so it just makes me wonder if my car is lugging or just not good at lower than 2500rpm shifts?

3. Last question I promise, I was wondering if calculating my mileage by filling up could vary depending on different gas stations and how their pumps stop when full. Do you top off the gas until it runs out?

I appreciate any comments.

Brian

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Old 02-09-2011, 09:22 AM   #2 (permalink)
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Filling up till the pump clicks off should be close enough, filling it till it over flows is a bad idea because at that point there is no space for the fuel to expand as it warms up.
Your 4 speed's 4 gear is pretty close to the same gear ratio as the 5th gear ratio that the 5 speeds have, it's just more space between each ratio, you could go with a CRX HF transmission and get a slightly better top gear ratio but I would only bother with that if you need to replace your transmission anyway.
Any of the lighter weight honda civic rims or crx rims will fit your car, the crx hf has narrower thiner steel rims that are lighter weight but look like plane steel rims, the civic vx, civic hx, early civic hybrid, first generation honda insight all have light weight rims that will bolt right on without issue.
I've always gotten my best mileage with stock exhaust from the dealership, the stock exhaust also has a warranty for as long as you own it so if you find your self replacing exhaust systems due to rust it's well worth it, they are also not that much more then auto part store brand exhausts but they are much better quality.
As for other crx hf parts that would fit on the civic hatch back, there is not alot, you could swap in the engine and ecu, but just like swapping in a transmission you might as well wait till it needs to be done anyway.
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Old 02-10-2011, 04:14 AM   #3 (permalink)
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#1 - My Baby - '91 Honda Civic Hatchback DX
90 day: 35.4 mpg (US)

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Hello Brian, Welcome to the site.

My you're coming out of the gates a'runnin. Lets see if I can answer some of your inquires off the top of my head this late into a sleepless night,...

>1. I am wondering how close the CRX is to mine.
CRX's are smaller, lighter, more streamlinded versions of the Civics. They will beat a hatchback in MPG on any road even though many of them have the exact same drivetrain.

>My speedometer has a small 55 making me think this indicates the best speed
Naw, That's just some 70's fuel scare thing.

>what is the most fuel efficient constant speed
My best constant speed tanks have been at interstate speeds of 75+mph where I'd fill up and drive for some 400 miles straight only stopping again for more gas. (The not stopping part could have had something to do with it.) Otherwise I've been having some positive results with the whole 45mph max thing I've been doing for the last few months.

>my car doesn't come with a tach either
Yeah, my DXs didn't come with one either. Aftermarket tachs are easy enough to install but there is an easier way,... Just get a SI gauge cluster, all the wires for the tach are in the car, you just need a cluster with a tach.

>have had problems starting
I don't p&g but if you are having problems starting after being parked for awhile then I've some advice that helps with my Civics. Turn the key until the gauge warning lights come on. Wait until the amber engine light goes out before starting the engine. The fuelline can and will lose pressure. The fuel pump pressurizes the line while the engine light is on. The engine can't start without fuel and the battery might not have enough juice to turn the fuel pump and the engine at the same time.
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Old 02-10-2011, 09:29 PM   #4 (permalink)
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Quote:
Originally Posted by Ryland View Post
Filling up till the pump clicks off should be close enough, filling it till it over flows is a bad idea because at that point there is no space for the fuel to expand as it warms up.
Your 4 speed's 4 gear is pretty close to the same gear ratio as the 5th gear ratio that the 5 speeds have, it's just more space between each ratio, you could go with a CRX HF transmission and get a slightly better top gear ratio but I would only bother with that if you need to replace your transmission anyway.
Any of the lighter weight honda civic rims or crx rims will fit your car, the crx hf has narrower thiner steel rims that are lighter weight but look like plane steel rims, the civic vx, civic hx, early civic hybrid, first generation honda insight all have light weight rims that will bolt right on without issue.
I've always gotten my best mileage with stock exhaust from the dealership, the stock exhaust also has a warranty for as long as you own it so if you find your self replacing exhaust systems due to rust it's well worth it, they are also not that much more then auto part store brand exhausts but they are much better quality.
As for other crx hf parts that would fit on the civic hatch back, there is not alot, you could swap in the engine and ecu, but just like swapping in a transmission you might as well wait till it needs to be done anyway.
Thanks for the info....Now I understand about how the 4 speed can still get the same FE as the 5 speed I guess at least I don't have as many shift changes to deal with
Also, I had always wondered when I fill up if different pumps/gas stations would stop differently and therefore my FE would be off, but maybe they are actually closer than I think. I did a 40 mile fill up tonight and it only came to be about 34mpg (I was trying to neutral glide a lot, especially up to stoplights), but I was hoping to do better. I have a bad left front cv axle that is now starting to make a lot of noise so that is bothersome and I need to fix it sometime (although I think the boot has been torn for a year and a half.
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Old 02-10-2011, 09:46 PM   #5 (permalink)
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FlatBlackHatch - '91 Honda Civic Hatchback Standard
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Quote:
Originally Posted by Tri91 View Post
Hello Brian, Welcome to the site.

My you're coming out of the gates a'runnin. Lets see if I can answer some of your inquires off the top of my head this late into a sleepless night,...

>1. I am wondering how close the CRX is to mine.
CRX's are smaller, lighter, more streamlinded versions of the Civics. They will beat a hatchback in MPG on any road even though many of them have the exact same drivetrain.

>My speedometer has a small 55 making me think this indicates the best speed
Naw, That's just some 70's fuel scare thing.

>what is the most fuel efficient constant speed
My best constant speed tanks have been at interstate speeds of 75+mph where I'd fill up and drive for some 400 miles straight only stopping again for more gas. (The not stopping part could have had something to do with it.) Otherwise I've been having some positive results with the whole 45mph max thing I've been doing for the last few months.

>my car doesn't come with a tach either
Yeah, my DXs didn't come with one either. Aftermarket tachs are easy enough to install but there is an easier way,... Just get a SI gauge cluster, all the wires for the tach are in the car, you just need a cluster with a tach.

>have had problems starting
I don't p&g but if you are having problems starting after being parked for awhile then I've some advice that helps with my Civics. Turn the key until the gauge warning lights come on. Wait until the amber engine light goes out before starting the engine. The fuelline can and will lose pressure. The fuel pump pressurizes the line while the engine light is on. The engine can't start without fuel and the battery might not have enough juice to turn the fuel pump and the engine at the same time.
Thanks for the compliment.
That makes sense about the 55 mph. I guess it's just a good reminder.
The 75 mph constant speed sounds pretty high, since the RPM's at that speed would be high, plus the air drag on the car. I'm trying to figure out if anyone with a fuel feedback guage (like supermid or mpguino) for our cars can tell us exactly which speed gives the best instant FE.
I never looked into adding a tach, although now that I have figured out my gear ratio's / rpm's using an online calculator, I now know my rpm's so I'm not sure what a tach would do to help me then.
Thanks for all your help.
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Old 02-10-2011, 11:08 PM   #6 (permalink)
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Quote:
Originally Posted by 91CivicHatch View Post
Also, I had always wondered when I fill up if different pumps/gas stations would stop differently and therefore my FE would be off, but maybe they are actually closer than I think. I did a 40 mile fill up tonight and it only came to be about 34mpg (I was trying to neutral glide a lot, especially up to stoplights), but I was hoping to do better. I have a bad left front cv axle that is now starting to make a lot of noise so that is bothersome and I need to fix it sometime (although I think the boot has been torn for a year and a half.
If you are only putting a gallon of gas in the car then tempature is going to play as much of a roll as anything else, the fuel in the return line is warmed up and heads back to the tank, a 40 mile trip the fuel in the tank has warmed up a reasonable amount and at that point is taking up a bit more space, this is why it can appear that your fuel level has dropped while parked over night.

As for your driving style, keep it in gear and take your foot off the gas pedal, if your engine is warmed up, oil pressure high enough, engine speed above I think 1,100 RPM or so and then Honda's will cut the fuel injector so instead of burning a quarter of a gallon per hour or whatever your engine uses at idle it's using nothing.
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Old 02-11-2011, 09:17 AM   #7 (permalink)
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Quote:
Originally Posted by Ryland View Post
If you are only putting a gallon of gas in the car then tempature is going to play as much of a roll as anything else, the fuel in the return line is warmed up and heads back to the tank, a 40 mile trip the fuel in the tank has warmed up a reasonable amount and at that point is taking up a bit more space, this is why it can appear that your fuel level has dropped while parked over night.

As for your driving style, keep it in gear and take your foot off the gas pedal, if your engine is warmed up, oil pressure high enough, engine speed above I think 1,100 RPM or so and then Honda's will cut the fuel injector so instead of burning a quarter of a gallon per hour or whatever your engine uses at idle it's using nothing.
Ryland, thanks for that explanation about gas. That makes sense because this morning I tried another test. I filled up at the same station as light night and numbers were 27mi/.78g = 34.68mpg. Then I filled up when I got closer to work and got 12.8mi/.836g = 15.4mpg. There is no way in my car I could get that low on a tank, and since the temperature here was near freezing, that could have played a roll (or the gas pumps could be different). I guess I was trying to find a way to test out techniques quicker, but maybe I need to wait until half a tank or else wait for the full tank to check.
I had read about DFCO, so I do use that sometimes. I was trying neutral from a far distance to get me to the light, but I may try more DFCO this time. I think you are right about the rpm's because for me in 4th gear, you can feel the car start to sputter when down to 25 which I think is around 1200 rpm. Hopefully my oil pressure is good then.
Also, just FYI, my daily commute is 25 miles one way. I don't take any interstates, so it's pretty much suburban traffic with a good number of lights and roads with PSL of 55 or 45 mostly.
Thanks for your help so far!
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Old 02-11-2011, 02:07 PM   #8 (permalink)
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Quote:
Originally Posted by 91CivicHatch View Post
Ryland, thanks for that explanation about gas. That makes sense because this morning I tried another test. I filled up at the same station as light night and numbers were 27mi/.78g = 34.68mpg. Then I filled up when I got closer to work and got 12.8mi/.836g = 15.4mpg. There is no way in my car I could get that low on a tank, and since the temperature here was near freezing, that could have played a roll (or the gas pumps could be different).
The errors and inconsistencies (tilt angle, nozzle insertion, flow cut-off) when filling up the tank is going to be huge with such small fills.

Quote:
I had read about DFCO, so I do use that sometimes. I was trying neutral from a far distance to get me to the light, but I may try more DFCO this time.
Coasting in neutral is more fuel efficient than DFCO from my experience.
I was using DFCO a lot, and driving a lot slower, but it's coasting that finally improved my fuel economy beyond what the car is officially rated for.

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