Rotary Fuel Efficient at Performance?
07-13-2011 | 04:47 PM
#1
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Rotary Fuel Efficient at Performance?
I read that the '91 Mazda 787 Le-Mans car dominated because its racing four rotor wankel engine was very good on fuel and pitted less than the competition using standard piston engines.
On my RX-8 I have noticed poor fuel economy in normal driving conditions but when I push it hard, I don't notice the fuel gauge going down much faster. Is it true that the rotary engine is more efficient than a comparable piston based engine at performance?
On my RX-8 I have noticed poor fuel economy in normal driving conditions but when I push it hard, I don't notice the fuel gauge going down much faster. Is it true that the rotary engine is more efficient than a comparable piston based engine at performance?
07-13-2011 | 05:05 PM
#2
I'm having a hard time telling if you're trolling or not but I'll give this a shot.
Fuel economy is NOT our cars strong point. A comparable in power 4-cylinder is going to be much better on fuel.
Fuel economy is NOT our cars strong point. A comparable in power 4-cylinder is going to be much better on fuel.
07-13-2011 | 06:14 PM
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Rickeo I think you should read his post a bit more. It actually wouldn't surprise me if you beat on an s2k that it would get worse gas mileage than an 8.
When I beat on my car, my gas mileage doesn't suffer alot. I've heard this from many FD owners. Then again, my car is relatively weak for a modified FD. Not sure about N/A cars but I wouldn't be surprised. I've driven with heavily modified, high powered FDs and they don't seem to lose that much more fuel than me either. When those guys push their cars hard I think their fuel economy drop is much higher than mine but they don't have to push their cars as hard to match my performance. IMO, a rotary will not lose that much more on gas comparitively to a piston car.
I read that the '91 Mazda 787 Le-Mans car dominated because its racing four rotor wankel engine was very good on fuel and pitted less than the competition using standard piston engines.
On my RX-8 I have noticed poor fuel economy in normal driving conditions but when I push it hard, I don't notice the fuel gauge going down much faster. Is it true that the rotary engine is more efficient than a comparable piston based engine at performance?
On my RX-8 I have noticed poor fuel economy in normal driving conditions but when I push it hard, I don't notice the fuel gauge going down much faster. Is it true that the rotary engine is more efficient than a comparable piston based engine at performance?
Last edited by Supernaut6; 07-13-2011 at 06:20 PM.
07-13-2011 | 09:39 PM
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So again to be more clear, I am not talking about standard fuel economy. I am talking about during high performance conditions when the engine is utilized at 100% for an extended period of time, like in a race. I've heard that rotaries hold on to the energy they produce longer through heat retention or something. I was hoping someone with more mechanical experience then me could give me their input.
07-13-2011 | 09:41 PM
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07-13-2011 | 09:48 PM
#6
Eric Meyer recently posted in a thread that he gets about 70 miles per tank in the Continental Challenge car during race conditions. I'm not sure how large of a fuel cell he runs though. I wouldn't call that efficient unless it was a 7 gallon tank.
From what i read here 7-10 mpg during an HPDE is the average for an 8. My friend's e36 got about the same as well as my friend with the 993 911. That being said, i would call it about average for a car at the track.
From what i read here 7-10 mpg during an HPDE is the average for an 8. My friend's e36 got about the same as well as my friend with the 993 911. That being said, i would call it about average for a car at the track.
Last edited by fuztupnz; 07-13-2011 at 09:52 PM.
07-13-2011 | 10:10 PM
#7
I would agree with the original poster's premise. In my experience, the rotary's efficiency achilles heel is idle economy and, to a lesser extent, part throttle economy. I strongly suspect that an idle-stop system would massively improve economy in the RX-8; but then Mazda would have to have used better ignition coils (like the ones BHR sells) to stave off flooding.
07-14-2011 | 12:27 AM
#8
I HATE SPEEDBUMPS!
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Pressing the gas hard makes the fuel efficient? To my knowledge, that is impossible, specially for the rx8. I don't know how you got that theory, but this is not true in away your saying it.
07-14-2011 | 09:09 AM
#9
Fuel efficiency at full throttle usage is almost entirely based on how much horsepower you are making.
In the end, the number 1 contributing factor by a long shot is that for X amount of power, you need Y amount of fuel. The more power you call for, the more fuel you use. There is exactly zero ways around this for an internal combustion engine, regardless of type. That 30mpg 300hp Mustang ISN'T getting better gas mileage on the track than we are. Unless it's the pace car. Rotaries get less energy out of a drop of fuel than piston engines they are competing with, (the natural thermal disadvantage we have), so yes, our race-condition fuel mileage is worse than the respective ~230hp cars. (You use crank power for this, since you are still paying fuel for the drivetrain power loss, regardless of car) However, it's not like it's crazy less. 9mpg is typical for a stock RX-8 track day. I don't know the decimal, but I've also seen cars up to around 300hp also getting "9mpg" probably a difference in the decimal, but it's not big enough to shift a whole number.
Another thing to look at is the Grand Am series GT class. The 3-rotor RX-8s are allowed a 20 gallon tank, where the other cars in the class are only allowed an 18.5 gallon tank, and they pit roughly the same amount.
Edit:
Note that I say "power you are making", not "speed". A car with 15% more power but 15% more aerodynamic drag is probably going to be using more fuel, but going no faster (roughly) Same issue with drivetrain loss, etc... If the engine is making the power, it's using the fuel, regardless of where that power is being applied (aero, drivetrain loss, to the wheels, or something else like accessories)
In the end, the number 1 contributing factor by a long shot is that for X amount of power, you need Y amount of fuel. The more power you call for, the more fuel you use. There is exactly zero ways around this for an internal combustion engine, regardless of type. That 30mpg 300hp Mustang ISN'T getting better gas mileage on the track than we are. Unless it's the pace car. Rotaries get less energy out of a drop of fuel than piston engines they are competing with, (the natural thermal disadvantage we have), so yes, our race-condition fuel mileage is worse than the respective ~230hp cars. (You use crank power for this, since you are still paying fuel for the drivetrain power loss, regardless of car) However, it's not like it's crazy less. 9mpg is typical for a stock RX-8 track day. I don't know the decimal, but I've also seen cars up to around 300hp also getting "9mpg" probably a difference in the decimal, but it's not big enough to shift a whole number.
Another thing to look at is the Grand Am series GT class. The 3-rotor RX-8s are allowed a 20 gallon tank, where the other cars in the class are only allowed an 18.5 gallon tank, and they pit roughly the same amount.
Edit:
Note that I say "power you are making", not "speed". A car with 15% more power but 15% more aerodynamic drag is probably going to be using more fuel, but going no faster (roughly) Same issue with drivetrain loss, etc... If the engine is making the power, it's using the fuel, regardless of where that power is being applied (aero, drivetrain loss, to the wheels, or something else like accessories)
Last edited by RIWWP; 07-14-2011 at 09:16 AM.
07-14-2011 | 09:27 AM
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07-14-2011 | 09:43 AM
#12
tjb
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From: Louisiana
It had less to do with fuel and more to do with other factors. Other cars breaking down, Mazda's plan to push their drivers to the limit, and some technology like tire sensors and ceramic seals.
07-14-2011 | 09:44 AM
#13
Fuel efficiency at full throttle usage is almost entirely based on how much horsepower you are making.
In the end, the number 1 contributing factor by a long shot is that for X amount of power, you need Y amount of fuel. The more power you call for, the more fuel you use. There is exactly zero ways around this for an internal combustion engine, regardless of type. That 30mpg 300hp Mustang ISN'T getting better gas mileage on the track than we are. Unless it's the pace car. Rotaries get less energy out of a drop of fuel than piston engines they are competing with, (the natural thermal disadvantage we have), so yes, our race-condition fuel mileage is worse than the respective ~230hp cars. (You use crank power for this, since you are still paying fuel for the drivetrain power loss, regardless of car) However, it's not like it's crazy less. 9mpg is typical for a stock RX-8 track day. I don't know the decimal, but I've also seen cars up to around 300hp also getting "9mpg" probably a difference in the decimal, but it's not big enough to shift a whole number.
Another thing to look at is the Grand Am series GT class. The 3-rotor RX-8s are allowed a 20 gallon tank, where the other cars in the class are only allowed an 18.5 gallon tank, and they pit roughly the same amount.
Edit:
Note that I say "power you are making", not "speed". A car with 15% more power but 15% more aerodynamic drag is probably going to be using more fuel, but going no faster (roughly) Same issue with drivetrain loss, etc... If the engine is making the power, it's using the fuel, regardless of where that power is being applied (aero, drivetrain loss, to the wheels, or something else like accessories)
In the end, the number 1 contributing factor by a long shot is that for X amount of power, you need Y amount of fuel. The more power you call for, the more fuel you use. There is exactly zero ways around this for an internal combustion engine, regardless of type. That 30mpg 300hp Mustang ISN'T getting better gas mileage on the track than we are. Unless it's the pace car. Rotaries get less energy out of a drop of fuel than piston engines they are competing with, (the natural thermal disadvantage we have), so yes, our race-condition fuel mileage is worse than the respective ~230hp cars. (You use crank power for this, since you are still paying fuel for the drivetrain power loss, regardless of car) However, it's not like it's crazy less. 9mpg is typical for a stock RX-8 track day. I don't know the decimal, but I've also seen cars up to around 300hp also getting "9mpg" probably a difference in the decimal, but it's not big enough to shift a whole number.
Another thing to look at is the Grand Am series GT class. The 3-rotor RX-8s are allowed a 20 gallon tank, where the other cars in the class are only allowed an 18.5 gallon tank, and they pit roughly the same amount.
Edit:
Note that I say "power you are making", not "speed". A car with 15% more power but 15% more aerodynamic drag is probably going to be using more fuel, but going no faster (roughly) Same issue with drivetrain loss, etc... If the engine is making the power, it's using the fuel, regardless of where that power is being applied (aero, drivetrain loss, to the wheels, or something else like accessories)
07-14-2011 | 10:03 AM
#14
This discussion reminds me of the E80 ethanol vs. gasoline argument. The E80 is certainly more environmentally friendly at the tailpipe, but since it is has ~30% less energy per volume it's actually less friendly in the long run since you have to burn more for comparable power.
There's no free lunch. It takes energy to do work. More work = more energy required. The best we can do is to burn the fuel more efficiently, and to reduce weight and aerodynamic drag.
There's no free lunch. It takes energy to do work. More work = more energy required. The best we can do is to burn the fuel more efficiently, and to reduce weight and aerodynamic drag.
07-14-2011 | 10:04 AM
#15
It also wasn't losing power the whole period of the race, like was typical of the piston engines of that era. They would end the race with internal damage, bent parts, barely idle, etc... The 787B just purred perfectly fine at the end, ready for another race. So I'd expect that it's speed didn't drop off the way most cars did.
This piston-powered speed drop off and internal engine damage isn't common in today's Lemans races. The last one a few weeks ago, the fastest laps of the race were in the last hour.
A c6 Z06 will get roughly 6-7 mpg when hustled around a track which is far more efficient than our beloved 8 considering the fact that it has double the horsepower and triple the torque. It all come down to what riwwp has stated, but with a twist. It's very aerodynamic which makes it slippery in air creating less drag. The twist is that it weighs the same as an 8. Same weight, more aerodynamic, and more power make it more efficient. You may say that 7mpg is less efficient than 9, but in reality it isn't if you look at the power it's making per drop of gas as pointed out above.
For example:
The difference between 2 MPG and 3 MPG doesn't seem like much, only 1 MPG. But 2 MPG is equal to .5 gallons per mile, or 50 gallons per 100 miles. 3 MPG is 3.33 gallons per mile, or 33.33 gallons per 100 miles. Using 16.6 gallons less per 100 miles by that 1mpg change. That's more than our fuel capacity.
At the high range, look at the difference between 50mpg and 60mpg. 50mpg uses 2 gallons per 100miles, 60mpg uses 1.66 gallons per 100 miles. 10 miles per gallon increase only saves you 0.4 gallons.
In races, they typically use Pounds of fuel per Lap or per Minute. Pounds, because it's faster and easier to weight the fuel than it is to try to get a volume measure. And they don't care how many miles, only how long they can run on the tank of fuel. What lap will they run out on.
07-14-2011 | 10:14 AM
#16
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787B was allowed to weight at 830 kg, whereas Jaguar and Sauber Mercedes were at 1000 kg. Huge difference at such scale
Also, both these piston powered cars were way more powerful than Mazda, and still were able to meet same fuel consumption formula...
Just google what BSFC can achieve Honda engine´s and such....
07-14-2011 | 10:14 AM
#17
tjb
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Someone correct me if I'm wrong but the way I understand it, it's not so much they pitted less but rather their pits were shorter...not switching drivers as much and knowing what tires needed more attention with sensors. Those small fractions start adding up on a race that long. Johnny Hebert collapsed when he got out just to show you how dedicated they were to shaving time.
07-14-2011 | 10:19 AM
#18
They won once the cars ahead of them failed.
Mazda was not the favorite to win, but the three Mazdas started on 19th (#55), 23rd (#18) and 30th (#56), despite being the 12th, 17th and 24th fastest qualifiers respectively. The new 3.5 litre cars were given the first grid positions, moving everyone else back by seven places. On the day before the race, team manager Ohashi decided to drop his usual conservative strategy and instructed the drivers of the #55 car to drive as if it were a short sprint race.
The decision was made based on the reliability of the cars demonstrated in the Paul Ricard tests, as well as the car's exceptional fuel economy, which meant that the carefully learned driving techniques intended to preserve the fuel allowance were no longer a critical part of the team's strategy.
In the early stages of the race, the #55 car made its way to third place with the #18 car behind it 2 laps down. The #18 had a lower gear ratio setup meaning the car used less fuel but was 20 km/h (12 mph) slower. The #55 would by night, move into second place when the Mercedes-Benz C11 of Michael Schumacher, Fritz Kreutzpointner and Karl Wendlinger spun off and later pitted with a gearbox problem. It soon became obvious that the leading car had slowed down to preserve its fuel allowance and an air of disbelief spread around the Mazda pit as it became obvious with six hours to run that there was a chance of victory.
At the 22nd hour, fate took a hand and the #55 car finally took the lead after the C11 of Alain Ferte was forced to pit with mechanical problems. At the last pit-stop, Herbert asked to stay in the car, and went on to take the 787B across the finish line first, completing 362 laps and covering 4932.2 km ( both new records for the recently modified circuit ). The two other cars finished sixth (#18) and eighth (#56). Three Jaguar XJR-12s and a sole Mercedes filled out positions two through five.
Herbert was so dehydrated that he had to be assisted out of the car and taken to the circuit's medical centre. As a result, he was unable to make it to the podium, leaving Weidler and Gatchot to take up the celebrations. He later commented in a magazine interview that some “dodgy” spaghetti he ate before his shift was the cause, but it is more likely that his drink bottle wasn't replenished when he chose to stay in the car for the remaining 40 minutes of the race. The replacement driver would normally carry his own bottle into the car during a changeover as they all had their own preferred drinks.
The winning car ran without a hitch apart from a blown headlamp bulb and a precautionary rear wheel bearing change on the driver's side of the car, when a regular check during a pit-stop showed it to be overheating slightly.[5]
The decision was made based on the reliability of the cars demonstrated in the Paul Ricard tests, as well as the car's exceptional fuel economy, which meant that the carefully learned driving techniques intended to preserve the fuel allowance were no longer a critical part of the team's strategy.
In the early stages of the race, the #55 car made its way to third place with the #18 car behind it 2 laps down. The #18 had a lower gear ratio setup meaning the car used less fuel but was 20 km/h (12 mph) slower. The #55 would by night, move into second place when the Mercedes-Benz C11 of Michael Schumacher, Fritz Kreutzpointner and Karl Wendlinger spun off and later pitted with a gearbox problem. It soon became obvious that the leading car had slowed down to preserve its fuel allowance and an air of disbelief spread around the Mazda pit as it became obvious with six hours to run that there was a chance of victory.
At the 22nd hour, fate took a hand and the #55 car finally took the lead after the C11 of Alain Ferte was forced to pit with mechanical problems. At the last pit-stop, Herbert asked to stay in the car, and went on to take the 787B across the finish line first, completing 362 laps and covering 4932.2 km ( both new records for the recently modified circuit ). The two other cars finished sixth (#18) and eighth (#56). Three Jaguar XJR-12s and a sole Mercedes filled out positions two through five.
Herbert was so dehydrated that he had to be assisted out of the car and taken to the circuit's medical centre. As a result, he was unable to make it to the podium, leaving Weidler and Gatchot to take up the celebrations. He later commented in a magazine interview that some “dodgy” spaghetti he ate before his shift was the cause, but it is more likely that his drink bottle wasn't replenished when he chose to stay in the car for the remaining 40 minutes of the race. The replacement driver would normally carry his own bottle into the car during a changeover as they all had their own preferred drinks.
The winning car ran without a hitch apart from a blown headlamp bulb and a precautionary rear wheel bearing change on the driver's side of the car, when a regular check during a pit-stop showed it to be overheating slightly.[5]
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