How can I get better mileage?
05-10-05, 08:53 PM
#52
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Originally Posted by Icemark
Infact I bet, if you disconnect the 5th gear (over the top ) switch, it will have more of an effect on mileage than the O2 sensor
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05-10-05, 08:55 PM
#53
Former Moderator. RIP Icemark.
Originally Posted by wotnartd
Okay, so I know I'm stupid, what the hell's a FC? I've been reading it a few times, and well, I'm stumped.
But the simple answer is FC= 2nd gen RX-7
05-10-05, 08:56 PM
#54
Former Moderator. RIP Icemark.
Originally Posted by Madrx7racer
another issue I should fix then....lol
05-10-05, 08:57 PM
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Originally Posted by wotnartd
Okay, so I know I'm stupid, what the hell's a FC? I've been reading it a few times, and well, I'm stumped.
READ THIS AND DON'T POST UNTIL UR DONE......WITH ALL OF IT!!!
05-10-05, 09:05 PM
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Originally Posted by Icemark
nah, it was said more to prove a point. The 5th gear (over the Top) switch effects little besides emmissions.
05-10-05, 10:57 PM
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Originally Posted by dDuB
I get 17 - 17.5 mpg FULL city driving, haven't even tested highway because I never use it with any of my commutes.
It's easy to get good gas mileage, even with a modded engine. My engine is recently rebuilt and ported by me, full exhaust, CAI, alum flywheel/good clutch, underdrive main pulley, advanced timing, bla bla bla. I am also untuned still, running all this off the stock original (read uncleaned) injectors, TII fuel pump, and no tuning.
I found that weight reduction as well as a full tuneup can really help mpg. I have around 230 to 250 lbs taken off my car with full interior minus storage bins, and have done a full tuneup. The thing that helped me the most was tweaking the idle and resetting the TPS. I've also been running with my O2 sensor not working (wire melted on the header, still haven't fixed that) and my mpg didn't change noticeably.
It's easy to get good gas mileage, even with a modded engine. My engine is recently rebuilt and ported by me, full exhaust, CAI, alum flywheel/good clutch, underdrive main pulley, advanced timing, bla bla bla. I am also untuned still, running all this off the stock original (read uncleaned) injectors, TII fuel pump, and no tuning.
I found that weight reduction as well as a full tuneup can really help mpg. I have around 230 to 250 lbs taken off my car with full interior minus storage bins, and have done a full tuneup. The thing that helped me the most was tweaking the idle and resetting the TPS. I've also been running with my O2 sensor not working (wire melted on the header, still haven't fixed that) and my mpg didn't change noticeably.
I can't say for shure, but I have noticed that S4 seem to get better gas milage than S5s, so I think weight has something to do with that. THe S5 are heavier than the S4, but then again the EPA mpg seem the same, can't remember the numbers....
Then again I am most likely wrong....
gil
05-10-05, 11:03 PM
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Of course weight has something to do with mpg. The lighter the car the less throttle/power needed to move it faster or get it going. I really think the weight reduction I've done helped a bit.
05-10-05, 11:13 PM
#61
Other than the emissions stuff, the only effect of the 5th gear switch is to prevent the shift-up light.
It's hard to get into closed loop mode in 4th, but it is possible.
As for fuel economy related things, I'm actually working on making my NA as efficient as possible. I don't expect 30mpg (well, maybe once or twice with a tailwind), but I'd like to be 25+mpg highway pretty constantly. Right now I get 19-21, depending on how I drive it (like the winding road run tonight will lead to worse economy... I don't think I was under 4k RPM for more than 20% of the run).
On my list of things I've done/am planning to do:
* Replace the spark plugs regularly (every 5k or so). In addition to reducing power, worn plugs reduce fuel economy. The engine still runs fine, but you can feel the difference.
* CD Ignition box. Crane HI-6 or a MSD 6A, either one works fine. This gives you a more powerful spark up high, and multiple sparks down low. More complete combustion, more power up high (you can be misfiring and not feel it), smoother idle, better fuel economy... there's really no downside.
* Cleaned fuel injectors. Haven't done this yet, but it's a pretty good bet that 15+ year old fuel injectors aren't going to be putting out a perfect spray pattern. I'm not talking about running a tank of fuel injector cleaner through, I'm talking about sending them in to Cruzin Performance or RC Engineering or your local diesel shop for reverse flow ultrasonic cleaning, pintle cap replacement, flow testing, etc.
* SAFC-II. Standalone is better, many of us don't have modded enough cars to get any huge benefits out of a standalone, but a SAFC-II is quite nice. Especially for the NA guys, you can subtract a good deal of fuel without affecting performance. If you leave the O2 sensor in, you'll still help highway mileage due to the amount of time spent in open loop mode on the highway (hills, passing, etc), or you can remove the O2 input from the ECU and more or less tune it for a slightly lean A/F ratio. You'll also help mileage when running hard - it's amazing how much fuel you have to pull out up high to get the mixture somewhere close to stoich.
* Change the tranny/differential fluid to something synthetic and slippery. I hear Redline is good. Reduced drivetrain losses translate directly into better fuel economy & more power to the wheels.
* Repack your wheel bearings. It's a good idea anyway if you haven't done it, and the new grease might help a tiny bit. Mostly it's just a good idea.
* Check that your brakes aren't dragging. A slider that's not well lubricated, a sticking piston, missing retractor springs, hanging ebrake cable... in addition to heating the brakes and running through brake pads at an annoying rate, you lose fuel economy & power.
* Exhaust/intake: The easier the engine can breathe, the more power you get out of it, and the better fuel economy. The one "gotcha" here is that everyone wants to make a cold air intake. The colder the intake charge, the worse the fuel economy. If you really want great fuel economy, build a *hot* air intake. Or, fabricate something goofy with vacuum actuated flappers & some other jazz...
* Engine temperature. Not suggested, but I still have a point. The hotter the engine (within reason), the better your fuel economy. A 160F thermostat will get you better power, but a 195F thermostat will get you better fuel economy. I don't suggest this, given a rotary's issues with overheating, but if you rigged the thermostat to be always open and your engine is running fairly cold, your fuel economy will suffer.
Now, some easier things that don't require any sort of major mechanical or electrical work.
* Keep the darn tires inflated. Underinflated tires take more power to turn, wear out sooner, handle worse, etc.
* Close the windows & sunroof on the highway. I've noticed a 2-3mpg loss when running with the windows & sunroof open. The A/C compressor takes less power on the highway than the additional drag of the windows, especially since once the car is cooled down the A/C compressor will cycle on and off - it's not constantly on.
* Keep it below 3500 RPM on the highway. As has been noted, many people have observed that fuel economy is actually better at higher speeds, but going into open loop mode above 3500 RPM will negate any benefits due to the rather absurdly rich A/F ratios.
* Add more premix. The number I've seen around here is 85:1 or so for noticeable gains in fuel economy. The downside of this is that you'll contaminate the engine oil significantly more, and have to change it more often. I'm not sure the fuel savings outweigh the additional cost of more oil changes, but it does work.
* Stay out of the go-fast pedal. It's great fun to lay into it at highway speeds, especially when occurring after a downshift, but any time your foot is digging in, the ECU is in open loop mode and dumping a lot of fuel. Also, drive without the cruise control. The cruise control has to wait until the car slows down to add gas for hills, and it *will* drop you out of closed loop mode. If you're very light on the gas (and lead the hills slightly so you can slow down a bit on the way up), you can stay in closed loop mode and gain some mileage.
Ehm... anything I'm missing?
-=Russ=-
It's hard to get into closed loop mode in 4th, but it is possible.
As for fuel economy related things, I'm actually working on making my NA as efficient as possible. I don't expect 30mpg (well, maybe once or twice with a tailwind), but I'd like to be 25+mpg highway pretty constantly. Right now I get 19-21, depending on how I drive it (like the winding road run tonight will lead to worse economy... I don't think I was under 4k RPM for more than 20% of the run).
On my list of things I've done/am planning to do:
* Replace the spark plugs regularly (every 5k or so). In addition to reducing power, worn plugs reduce fuel economy. The engine still runs fine, but you can feel the difference.
* CD Ignition box. Crane HI-6 or a MSD 6A, either one works fine. This gives you a more powerful spark up high, and multiple sparks down low. More complete combustion, more power up high (you can be misfiring and not feel it), smoother idle, better fuel economy... there's really no downside.
* Cleaned fuel injectors. Haven't done this yet, but it's a pretty good bet that 15+ year old fuel injectors aren't going to be putting out a perfect spray pattern. I'm not talking about running a tank of fuel injector cleaner through, I'm talking about sending them in to Cruzin Performance or RC Engineering or your local diesel shop for reverse flow ultrasonic cleaning, pintle cap replacement, flow testing, etc.
* SAFC-II. Standalone is better, many of us don't have modded enough cars to get any huge benefits out of a standalone, but a SAFC-II is quite nice. Especially for the NA guys, you can subtract a good deal of fuel without affecting performance. If you leave the O2 sensor in, you'll still help highway mileage due to the amount of time spent in open loop mode on the highway (hills, passing, etc), or you can remove the O2 input from the ECU and more or less tune it for a slightly lean A/F ratio. You'll also help mileage when running hard - it's amazing how much fuel you have to pull out up high to get the mixture somewhere close to stoich.
* Change the tranny/differential fluid to something synthetic and slippery. I hear Redline is good. Reduced drivetrain losses translate directly into better fuel economy & more power to the wheels.
* Repack your wheel bearings. It's a good idea anyway if you haven't done it, and the new grease might help a tiny bit. Mostly it's just a good idea.
* Check that your brakes aren't dragging. A slider that's not well lubricated, a sticking piston, missing retractor springs, hanging ebrake cable... in addition to heating the brakes and running through brake pads at an annoying rate, you lose fuel economy & power.
* Exhaust/intake: The easier the engine can breathe, the more power you get out of it, and the better fuel economy. The one "gotcha" here is that everyone wants to make a cold air intake. The colder the intake charge, the worse the fuel economy. If you really want great fuel economy, build a *hot* air intake. Or, fabricate something goofy with vacuum actuated flappers & some other jazz...
* Engine temperature. Not suggested, but I still have a point. The hotter the engine (within reason), the better your fuel economy. A 160F thermostat will get you better power, but a 195F thermostat will get you better fuel economy. I don't suggest this, given a rotary's issues with overheating, but if you rigged the thermostat to be always open and your engine is running fairly cold, your fuel economy will suffer.
Now, some easier things that don't require any sort of major mechanical or electrical work.
* Keep the darn tires inflated. Underinflated tires take more power to turn, wear out sooner, handle worse, etc.
* Close the windows & sunroof on the highway. I've noticed a 2-3mpg loss when running with the windows & sunroof open. The A/C compressor takes less power on the highway than the additional drag of the windows, especially since once the car is cooled down the A/C compressor will cycle on and off - it's not constantly on.
* Keep it below 3500 RPM on the highway. As has been noted, many people have observed that fuel economy is actually better at higher speeds, but going into open loop mode above 3500 RPM will negate any benefits due to the rather absurdly rich A/F ratios.
* Add more premix. The number I've seen around here is 85:1 or so for noticeable gains in fuel economy. The downside of this is that you'll contaminate the engine oil significantly more, and have to change it more often. I'm not sure the fuel savings outweigh the additional cost of more oil changes, but it does work.
* Stay out of the go-fast pedal. It's great fun to lay into it at highway speeds, especially when occurring after a downshift, but any time your foot is digging in, the ECU is in open loop mode and dumping a lot of fuel. Also, drive without the cruise control. The cruise control has to wait until the car slows down to add gas for hills, and it *will* drop you out of closed loop mode. If you're very light on the gas (and lead the hills slightly so you can slow down a bit on the way up), you can stay in closed loop mode and gain some mileage.
Ehm... anything I'm missing?
-=Russ=-
Last edited by Syonyk; 05-10-05 at 11:18 PM. Reason: Formatting for easier reading
05-11-05, 01:09 AM
#62
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Originally Posted by dDuB
Of course weight has something to do with mpg. The lighter the car the less throttle/power needed to move it faster or get it going. I really think the weight reduction I've done helped a bit.
5 pages over a gas mileage question.....cracks me up
05-11-05, 01:15 AM
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Originally Posted by jhammons01
You mean I shouldn't carry 200lbs worth of catalogues in the trunk while racing??
5 pages over a gas mileage question.....cracks me up
5 pages over a gas mileage question.....cracks me up
yet you read throw all of them.......
Gil
05-11-05, 09:26 AM
#65
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Very good list of things to do, Russ. Here are my thoughts on some of them:
1) Spark plug changes at 5K seems a little radical to me. I change mine every 15K, and notice no mileage degradation when they have over 10K on them...
2) CDI unit is on my wish list, way up there...
3) cleaned fuel injectors don't cut it, unless they were horrible to begin with. Noticed absolutely no mileage improvement after my injectors were cleaned. Brand spanking new injectors are on my wish list also (209K currently on mine, lol)...
4) Ain't worried about an SAFC- I drive in stoich 90% of the time anyway, and an SAFC isn't going to do that any better for me...
5) The slippery synthetic tranny/ diff fluids don't hurt, but didn't seem to help much, either. Maybe .1 mpg average, if that...
6) Cone filter didn't make a bit of difference with mileage. Open exhaust did a little, I think. Should have recorded numbers after I installed it, I dropped the ball on that one. My obsessive-compulsive behavior is failing me
7) Yes, warmer engines will give better economy, but a bigger factor is the outside air temps you're running in. In fact that is the biggest factor overall on my car...
8) Add all the premix you want, and let me know how it turns out. I saw marked improvements down around 80:1, but the freakin' blowby into the oil system was just too much. I'm talking oil changes every 1000 miles just to keep it under control. I'm still wondering if it's a normal thing with that much premix, or if it's the fault of the worn side housings (they're all still original, with about .002 wear at the 186K rebuild). New side housings will be installed at the 250K rebuild, and I'll have a better idea if my theory holds true...
As it is, I get 27 mpg with a 100:1 ratio (1.25 oz/ gal), so that level is perfectly fine in my book
And yeah, jhammons, these threads pop up every week, but some of us have some ood info to share with the rookies, and in my case, I had to correct some dubious information that was posted
1) Spark plug changes at 5K seems a little radical to me. I change mine every 15K, and notice no mileage degradation when they have over 10K on them...
2) CDI unit is on my wish list, way up there...
3) cleaned fuel injectors don't cut it, unless they were horrible to begin with. Noticed absolutely no mileage improvement after my injectors were cleaned. Brand spanking new injectors are on my wish list also (209K currently on mine, lol)...
4) Ain't worried about an SAFC- I drive in stoich 90% of the time anyway, and an SAFC isn't going to do that any better for me...
5) The slippery synthetic tranny/ diff fluids don't hurt, but didn't seem to help much, either. Maybe .1 mpg average, if that...
6) Cone filter didn't make a bit of difference with mileage. Open exhaust did a little, I think. Should have recorded numbers after I installed it, I dropped the ball on that one. My obsessive-compulsive behavior is failing me
7) Yes, warmer engines will give better economy, but a bigger factor is the outside air temps you're running in. In fact that is the biggest factor overall on my car...
8) Add all the premix you want, and let me know how it turns out. I saw marked improvements down around 80:1, but the freakin' blowby into the oil system was just too much. I'm talking oil changes every 1000 miles just to keep it under control. I'm still wondering if it's a normal thing with that much premix, or if it's the fault of the worn side housings (they're all still original, with about .002 wear at the 186K rebuild). New side housings will be installed at the 250K rebuild, and I'll have a better idea if my theory holds true...
As it is, I get 27 mpg with a 100:1 ratio (1.25 oz/ gal), so that level is perfectly fine in my book
And yeah, jhammons, these threads pop up every week, but some of us have some ood info to share with the rookies, and in my case, I had to correct some dubious information that was posted
05-11-05, 10:10 AM
#66
I get a lot of blowby into the oil with higher premix ratios as well... again, worn side housings & such are probably responsible. I figure the fuel economy gains aren't worth the additional cost of oil for the more frequent changes. I change the oil every 2000 or so, or when I get a "quart up" - that one time I ran 50:1 for a tank by mistake... yea. Oil change time.
It would be interesting to see what sort of effect cleaned injectors have on a car running 12-15mpg. How bad were your injectors when you sent them in?
I really think a big factor is how people drive. I know that without my SAFC, when I would take some of the local winding roads, I'd burn through a LOT of gas in short order. Never did do the math... I never wanted to know.
Also, with regards to the spark plug change interval, it sounds like you're a lot easier on your engine than many people. Sustained highway cruising is going to wear the plugs a lot less than WOT high RPM operation. It would be interesting to get dyno plots (preferably on an engine dyno) with varying spark plug conditions & ignition systems. More interesting would be fuel consumption plots - track how much fuel is needed to sustain a given power output for a given time.
-=Russ=-
It would be interesting to see what sort of effect cleaned injectors have on a car running 12-15mpg. How bad were your injectors when you sent them in?
I really think a big factor is how people drive. I know that without my SAFC, when I would take some of the local winding roads, I'd burn through a LOT of gas in short order. Never did do the math... I never wanted to know.
Also, with regards to the spark plug change interval, it sounds like you're a lot easier on your engine than many people. Sustained highway cruising is going to wear the plugs a lot less than WOT high RPM operation. It would be interesting to get dyno plots (preferably on an engine dyno) with varying spark plug conditions & ignition systems. More interesting would be fuel consumption plots - track how much fuel is needed to sustain a given power output for a given time.
-=Russ=-
05-11-05, 10:26 AM
#67
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10MPG here (on a good day), usually about 7.5MPG.... How bad is that huh....
I know I lose fuel from the filler cap when I do hard cornering, there is a pin sized hole in the cap, but a lot of fuel is going somewhere and I don't know where lol!
Funny original post :P
I know I lose fuel from the filler cap when I do hard cornering, there is a pin sized hole in the cap, but a lot of fuel is going somewhere and I don't know where lol!
Funny original post :P
05-11-05, 03:01 PM
#68
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Originally Posted by Syonyk
I get a lot of blowby into the oil with higher premix ratios as well... again, worn side housings & such are probably responsible. I figure the fuel economy gains aren't worth the additional cost of oil for the more frequent changes. I change the oil every 2000 or so, or when I get a "quart up" - that one time I ran 50:1 for a tank by mistake... yea. Oil change time.
It would be interesting to see what sort of effect cleaned injectors have on a car running 12-15mpg. How bad were your injectors when you sent them in?
I really think a big factor is how people drive. I know that without my SAFC, when I would take some of the local winding roads, I'd burn through a LOT of gas in short order. Never did do the math... I never wanted to know.
Also, with regards to the spark plug change interval, it sounds like you're a lot easier on your engine than many people. Sustained highway cruising is going to wear the plugs a lot less than WOT high RPM operation. It would be interesting to get dyno plots (preferably on an engine dyno) with varying spark plug conditions & ignition systems. More interesting would be fuel consumption plots - track how much fuel is needed to sustain a given power output for a given time.
-=Russ=-
It would be interesting to see what sort of effect cleaned injectors have on a car running 12-15mpg. How bad were your injectors when you sent them in?
I really think a big factor is how people drive. I know that without my SAFC, when I would take some of the local winding roads, I'd burn through a LOT of gas in short order. Never did do the math... I never wanted to know.
Also, with regards to the spark plug change interval, it sounds like you're a lot easier on your engine than many people. Sustained highway cruising is going to wear the plugs a lot less than WOT high RPM operation. It would be interesting to get dyno plots (preferably on an engine dyno) with varying spark plug conditions & ignition systems. More interesting would be fuel consumption plots - track how much fuel is needed to sustain a given power output for a given time.
-=Russ=-
My injectors weren't that bad, I guess. Slight improvement in flow #s after cleaned according to Cruzin's results...I'll let everyone know if the new injectors result in any significant gains, because they should be installed in the next couple of months...
And yeah, I'm not playing "Speed Racer" all the time. Gettin' too old for that, lol. She gets kicked in about 3 or 4 times a day, though, just for scenarios such as passing trucks, getting pissed off at slowpokes in the left lane, getting on the freeway, racing the occasional Civic or Mustang, that kind of thing...
05-11-05, 03:17 PM
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Originally Posted by WAYNE88N/A
And yeah, I'm not playing "Speed Racer" all the time. Gettin' too old for that, lol. She gets kicked in about 3 or 4 times a day, though, just for scenarios such as passing trucks, getting pissed off at slowpokes in the left lane, getting on the freeway, racing the occasional Civic or Mustang, that kind of thing...
NOt a "speed Racer" at all
Gil
05-11-05, 04:08 PM
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Originally Posted by TOOSHORT_88
i think my big 18's are sucking down my gas, how do i figure out what my gas milage is?
Assuming your tires are plus sized correctly with those 18's, you can fill up the tank, then drive the car, then fill it up again. Divide the miles you've driven since your last fill up into the number of gallons to fill up the second time. That's your fuel economy. That's how I do it. The fuel gauge is horrible.
05-11-05, 04:16 PM
#72
Lives on the Forum
If you want very accurate mileage results, top off the tank up to the filler neck before starting the test. After a couple of days of driving as you normally do, refill the tank up to the neck again. Miles traveled on the trip odometer divided by the number of gallons it took to fill her up the second time...
You can get accuracy down to the hundreths of a gallon, such as 26.702 mpg...
You can get accuracy down to the hundreths of a gallon, such as 26.702 mpg...
05-11-05, 06:01 PM
#74
Former Moderator. RIP Icemark.
Originally Posted by WAYNE88N/A
If you want very accurate mileage results, top off the tank up to the filler neck before starting the test. After a couple of days of driving as you normally do, refill the tank up to the neck again. Miles traveled on the trip odometer divided by the number of gallons it took to fill her up the second time...
You can get accuracy down to the hundreths of a gallon, such as 26.702 mpg...
You can get accuracy down to the hundreths of a gallon, such as 26.702 mpg...
05-11-05, 06:47 PM
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To help get better milage, the biggest thing you can do is watch your speed. If you are constintaly speeding you will use up more gas then if you take your time and go slower.