at what RPM?
11-01-07, 03:58 AM
#1
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at what RPM?
ok so for the last few weeks i've been testing my car everytime i fill up. where do i get the better gas milage? in my subaru i get better gas milage at low RPMs, but in the FC i cant figure it out. ive tried shifting at 2.5- 3.5 and ive also tried shifting and running around 6.5, so i thought id throw the question out and see what answers i get
11-01-07, 09:48 AM
#6
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In any car, you will get best mileage going the lowest RPM in the highest gear. So, you should get the best mileage in 5th gear at the lowest RPM your car can easily drive in.
11-01-07, 10:18 AM
#7
^^^^^^^
not true. you get the best fuel economy at the rpm the intake and exhaust are "tuned" for. For example I have a neon (don't laugh), that I have had two different tranny's in. One I did 60 at 3000 rpm the other I do 80 at 3000 rpm. In the first I got better fuel economy at 55-65 now I get better economy at 70-80. In the 7 I get better economy at 75 than at 65. I also get better economy hauling *** through the mountains at high rpm than toting around town.
not true. you get the best fuel economy at the rpm the intake and exhaust are "tuned" for. For example I have a neon (don't laugh), that I have had two different tranny's in. One I did 60 at 3000 rpm the other I do 80 at 3000 rpm. In the first I got better fuel economy at 55-65 now I get better economy at 70-80. In the 7 I get better economy at 75 than at 65. I also get better economy hauling *** through the mountains at high rpm than toting around town.
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11-01-07, 10:52 AM
#9
i forget if it was 60 or 65, but either or, the faster you go, the more wind resistance, so....the more horsepower its going to take to keep you going at that speed, which means its going to require more fuel...
it also depends on if you start and stop, start and stop or get one nice long cruise back and forth to work, etc. starting and stopping takes more gas. (duh)
it also depends on if you start and stop, start and stop or get one nice long cruise back and forth to work, etc. starting and stopping takes more gas. (duh)
11-01-07, 11:01 AM
#10
You have to realize that the rotary is not efficient in low rpm's. Typically, this means anything under 2500 rpm. Efficiency also drops above 3000 rpm. That 500 rpm range is the sweet spot in a rotary engine car.
For 40 mph, You should be in higher rpm in 4th gear, rather than bogging the car in 5th gear. In 5th, you'd be putting the engine under more load, which wastes more fuel.
For 40 mph, You should be in higher rpm in 4th gear, rather than bogging the car in 5th gear. In 5th, you'd be putting the engine under more load, which wastes more fuel.
11-01-07, 05:33 PM
#11
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If you advance the timing (NA only) you can gett better mileage when runnig slower. I still think that mine gets optimum mileage at 80ish.
Arround town, shifting at 3k, never exceeding 25% throttle, coasting to stop = 25 mpg
Highway, gently driving at 70 mph = 28 mpg
Highway driving averaging 75 mph (mostly doing 80, slowing for traffic) = 30mpg
Abuse (full throttle accelerations at any chance) = 17 mpg
The point where an RX7 makes maximum fuel economy is higher than most piston engine cars due to the efficiency peak at 2500-3000 rpm and the low drag coefficient.
I am running 15° advanced timing (about +4 mpg across the board and better low rev response).
Arround town, shifting at 3k, never exceeding 25% throttle, coasting to stop = 25 mpg
Highway, gently driving at 70 mph = 28 mpg
Highway driving averaging 75 mph (mostly doing 80, slowing for traffic) = 30mpg
Abuse (full throttle accelerations at any chance) = 17 mpg
The point where an RX7 makes maximum fuel economy is higher than most piston engine cars due to the efficiency peak at 2500-3000 rpm and the low drag coefficient.
I am running 15° advanced timing (about +4 mpg across the board and better low rev response).
11-01-07, 07:14 PM
#12
The stock shift light is designed for optimum fuel economy. Under super low throttle it tells you to shift at about 2500 rpm, under medium to high throttle it tells you to shift at about 4000rpm. Between super low and medium throttle it says to shift between 2500 and 4000rpm.
High throttle is better for gas mileage, although other behavior that tends to come with it - high mph and excessive braking - is bad for gas mileage. But practically speaking I'd strike a balance between mph and mpg on the freeway, unless your time is worthless. Likewise for practicality I don't drive at WOT all the time. Low city (not freeway) mph and a safe distance between you and the guy in front of you on the freeway is usually a good idea with nothing to lose. I mean, speeding to a stoplight or tailgating gives you nothing but gas lost to braking.
Advancing the timing increases the risk of detonation. You may be fine for now, but it will only take an instant for a strong detonation to pop your engine later. The NA has a large safety factor against detonation so there's a chance that you may never detonate. But why gamble your engine just for a little mpg? The engine costs $1500-$3000+ to rebuild. Going from 26 to 30mpg you save about $200 per 12,000 miles.
High throttle is better for gas mileage, although other behavior that tends to come with it - high mph and excessive braking - is bad for gas mileage. But practically speaking I'd strike a balance between mph and mpg on the freeway, unless your time is worthless. Likewise for practicality I don't drive at WOT all the time. Low city (not freeway) mph and a safe distance between you and the guy in front of you on the freeway is usually a good idea with nothing to lose. I mean, speeding to a stoplight or tailgating gives you nothing but gas lost to braking.
Advancing the timing increases the risk of detonation. You may be fine for now, but it will only take an instant for a strong detonation to pop your engine later. The NA has a large safety factor against detonation so there's a chance that you may never detonate. But why gamble your engine just for a little mpg? The engine costs $1500-$3000+ to rebuild. Going from 26 to 30mpg you save about $200 per 12,000 miles.
Last edited by ericgrau; 11-01-07 at 07:44 PM.
11-02-07, 01:26 AM
#14
lycanthrope
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^^^^^^^
not true. you get the best fuel economy at the rpm the intake and exhaust are "tuned" for. For example I have a neon (don't laugh), that I have had two different tranny's in. One I did 60 at 3000 rpm the other I do 80 at 3000 rpm. In the first I got better fuel economy at 55-65 now I get better economy at 70-80. In the 7 I get better economy at 75 than at 65. I also get better economy hauling *** through the mountains at high rpm than toting around town.
not true. you get the best fuel economy at the rpm the intake and exhaust are "tuned" for. For example I have a neon (don't laugh), that I have had two different tranny's in. One I did 60 at 3000 rpm the other I do 80 at 3000 rpm. In the first I got better fuel economy at 55-65 now I get better economy at 70-80. In the 7 I get better economy at 75 than at 65. I also get better economy hauling *** through the mountains at high rpm than toting around town.
same here, and now i have an reason to haul *** all the time
11-02-07, 10:41 AM
#17
Shell and Shell Canada actually had two different gasoline formulations. Until recently, Shell Canada wasn't part of the Top Tier Gas companies.
So what I gather from this discussion should be:
At a stoplight, as it turns green:
1. Put the car in first gear
2. Engage first gear with clutch, go WOT until 3k rpm
3. shift to second gear, go WOT until 3k rpm
4. shift to third gear, go WOT until 3k rpm
5. shift to fourth gear, go WOT until 3k rpm
6. shift to fifth gear, go WOT until cruising RPM
If I already went over cruising speed before step 6, just shift to fifth and attain cruising RPM?
So what I gather from this discussion should be:
At a stoplight, as it turns green:
1. Put the car in first gear
2. Engage first gear with clutch, go WOT until 3k rpm
3. shift to second gear, go WOT until 3k rpm
4. shift to third gear, go WOT until 3k rpm
5. shift to fourth gear, go WOT until 3k rpm
6. shift to fifth gear, go WOT until cruising RPM
If I already went over cruising speed before step 6, just shift to fifth and attain cruising RPM?
11-02-07, 10:44 AM
#18
Felix my wankel
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what about skipping gears
running 1st gear hard/faster then skipping to 3rd
or running 2nd hard skippin to 4th
running 1st gear hard/faster then skipping to 3rd
or running 2nd hard skippin to 4th
Last edited by brianw90; 11-02-07 at 11:00 AM.
11-02-07, 11:11 AM
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You guys gotta realize that the only way to save gas is not using a car. I know we love our cars so we just need to drive them. Don't baby them but don't push them either.
Here's another question: What's the best way to save time?
Just drive the car but coast THE HELL outta stops and lay off the throttle.
Also THINK about and look around for the best routes and stray away from heavy traffic.
The only SECRET is to DRIVE!
Here's another question: What's the best way to save time?
Just drive the car but coast THE HELL outta stops and lay off the throttle.
Also THINK about and look around for the best routes and stray away from heavy traffic.
The only SECRET is to DRIVE!
11-02-07, 12:26 PM
#22
Your Mileage May Vary
Ok, in a theoretical discussion there are two variables -Drag (wind resistance) and engine efficiency.
The drag (wind resistance) varies with the square of the velocity (speed). So-on a given car, you will always, always, ALWAYS need more horsepower to overcome wind resistance at 80mph vs. 60 mph.
But it is not quite that simple.
We are also powering this object (car) with a Rotary Engine-a Wankel. The Wankel efficiency (energy output/energy input) apparently varies greatly over the rpm range of the engine also it varies with load. Exactly how much, no one on this board really knows, but most will agree that the variation is substantial.
To really know if the FC3S is more efficient at one speed vs. another we would need to plot the drag of the FC at various speeds vs. the Wankle efficiency at the engine speed and Hp output required to overcome that Drag.
I suspect that we would find some surprises with this theoretical exercise.
In practice, the outcome is going to greatly affected by operating condition of the engine. Another strong influence is engine modification, particularly fuel and port timing mods.
BTW, I get 24 +/- on the highway and between 10 and 18 mpg in mixed city driving with my stock 1990 N/A Vert. 2 mpg less on the highway with the top down. Going fast on the highway doesn't seem to really hurt the mileage.
The drag (wind resistance) varies with the square of the velocity (speed). So-on a given car, you will always, always, ALWAYS need more horsepower to overcome wind resistance at 80mph vs. 60 mph.
But it is not quite that simple.
We are also powering this object (car) with a Rotary Engine-a Wankel. The Wankel efficiency (energy output/energy input) apparently varies greatly over the rpm range of the engine also it varies with load. Exactly how much, no one on this board really knows, but most will agree that the variation is substantial.
To really know if the FC3S is more efficient at one speed vs. another we would need to plot the drag of the FC at various speeds vs. the Wankle efficiency at the engine speed and Hp output required to overcome that Drag.
I suspect that we would find some surprises with this theoretical exercise.
In practice, the outcome is going to greatly affected by operating condition of the engine. Another strong influence is engine modification, particularly fuel and port timing mods.
BTW, I get 24 +/- on the highway and between 10 and 18 mpg in mixed city driving with my stock 1990 N/A Vert. 2 mpg less on the highway with the top down. Going fast on the highway doesn't seem to really hurt the mileage.
11-02-07, 06:15 PM
#24
Shell and Shell Canada actually had two different gasoline formulations. Until recently, Shell Canada wasn't part of the Top Tier Gas companies.
So what I gather from this discussion should be:
At a stoplight, as it turns green:
1. Put the car in first gear
2. Engage first gear with clutch, go WOT until 3k rpm
3. shift to second gear, go WOT until 3k rpm
4. shift to third gear, go WOT until 3k rpm
5. shift to fourth gear, go WOT until 3k rpm
6. shift to fifth gear, go WOT until cruising RPM
If I already went over cruising speed before step 6, just shift to fifth and attain cruising RPM?
So what I gather from this discussion should be:
At a stoplight, as it turns green:
1. Put the car in first gear
2. Engage first gear with clutch, go WOT until 3k rpm
3. shift to second gear, go WOT until 3k rpm
4. shift to third gear, go WOT until 3k rpm
5. shift to fourth gear, go WOT until 3k rpm
6. shift to fifth gear, go WOT until cruising RPM
If I already went over cruising speed before step 6, just shift to fifth and attain cruising RPM?
At a stoplight, as it turns green:
1. Put the car in first gear
2. Engage first gear with clutch, go WOT until 4k rpm
3. shift to second gear, go WOT until 4k rpm
4. shift to third gear, go WOT until 4k rpm
Except you stop as soon as you hit your desired speed (the lower the better). Ideally you'd also coast in neutral, then go back to WOT when you need to get back up to speed. This technique is called "burn and coast" and it's common in mpg competitions.
But the above might not be practical, especially if there are other cars on the road.
Drag is proportional to speed CUBED. Drag >> all. Optimal gas mileage probably comes at 55-60mph freeway, assuming your car is in tune, etc. This is the typical number for sports cars, for other cars it's even lower. I've seen people claim better mileage at higher speeds, but they also don't tend to get much mpg regardless. My car is in fine shape and I get better mpg at lower speeds. In the city you'd want to go below 55mph to avoid excessive braking. Probably 40mph, I dunno.
So in summary for best mpg: high throttle, low mph, shift when shift light says so, avoid unnecessary braking.
Last edited by ericgrau; 11-02-07 at 06:21 PM.
11-02-07, 06:36 PM
#25
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holy crap, i didnt think my post would be so popular and controversal! sweet! yea i get best gas milage when im at home playin Wii....gas is up to $3.00 here..sucks ***.
BUT! when i do drive i better better millage going ***** out.
BUT! when i do drive i better better millage going ***** out.