whats your mpg on RX450h?
03-13-17, 06:25 AM
#961
Lead Lap
In the city, the car benefits from recovered energy normally wasted during braking.
Whereas on the highway, there's (relatively/nearly) no regeneration going on - and the efficiency of the ICE is hampered by the process of converting somewhere between 3/4 and 2/3 of the ICE's energy into electricity (somewhere around 95% efficiency), then converted into 3-phase (somewhere again around 95% efficiency during that process), and then storing energy into the battery and/or converting that energy back into torque (again around 95% efficiency).
(Think of it like: 31 MPG x .95 x .95 x .95 = 26.6 and you can see where some of your MPG goes.)
One would expect higher efficiency of the ICE on steady highway speeds - and, it is - only there is loss in all of the conversion processes -- and that's where your mileage "suffers".
For those of us whose daily operation favors stop and slow traffic - the hybrid's the (seemingly) logical choice.
From what I've been able to discern, the mode for the "combined" MPG of the 350 series is around 21 MPG; whereas the mode for the MPG of the 450's is more like 26.5 MPG -- and while the 5.5 MPG as a number isn't remarkable - that it represents an extra 26% is noteworthy.
Unfortunately, that 26% mileage increase comes at a 30% price penalty for the Premium Fuel (at least here in Florida).
(Here's where the "I always run Regular in my Premium-Fuel-Required car" guys always chime in.)
Whereas on the highway, there's (relatively/nearly) no regeneration going on - and the efficiency of the ICE is hampered by the process of converting somewhere between 3/4 and 2/3 of the ICE's energy into electricity (somewhere around 95% efficiency), then converted into 3-phase (somewhere again around 95% efficiency during that process), and then storing energy into the battery and/or converting that energy back into torque (again around 95% efficiency).
(Think of it like: 31 MPG x .95 x .95 x .95 = 26.6 and you can see where some of your MPG goes.)
One would expect higher efficiency of the ICE on steady highway speeds - and, it is - only there is loss in all of the conversion processes -- and that's where your mileage "suffers".
For those of us whose daily operation favors stop and slow traffic - the hybrid's the (seemingly) logical choice.
From what I've been able to discern, the mode for the "combined" MPG of the 350 series is around 21 MPG; whereas the mode for the MPG of the 450's is more like 26.5 MPG -- and while the 5.5 MPG as a number isn't remarkable - that it represents an extra 26% is noteworthy.
Unfortunately, that 26% mileage increase comes at a 30% price penalty for the Premium Fuel (at least here in Florida).
(Here's where the "I always run Regular in my Premium-Fuel-Required car" guys always chime in.)
Last edited by NateJG; 03-13-17 at 09:30 AM. Reason: Tossed a Slow pitch for the Regular Fuel guys.
03-20-17, 04:37 AM
#962
Rookie
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One of the dealer just moved up to D- rating. https://www.bbb.org/losangelessilico...s/?review=true They must be jumping up and down with joy and patting each other's backs.
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On a different note, my friend drove my car down to San Diego (with me in it) from Los Angeles and recorded 27.5 mpg using his heavy foot. He kept the cruise at 75 mph and had many bursts above 90 mph around Camp Pendleton area. All done in S mode.
Still scratching my head about Lexus claim of higher MPG in city driving......
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On a different note, my friend drove my car down to San Diego (with me in it) from Los Angeles and recorded 27.5 mpg using his heavy foot. He kept the cruise at 75 mph and had many bursts above 90 mph around Camp Pendleton area. All done in S mode.
Still scratching my head about Lexus claim of higher MPG in city driving......
.
04-03-17, 12:28 PM
#963
Instructor
Your city/highway numbers definitely seem bass ackwards as they say. 21mpg is the very, very worse I've ever gotten in the city, and that was from short trip, brutal cold, blizzard like conditions. This winter has been fairly mild, floating above and below freezing day to day and I've been getting about 25-26mpg (summer is about 28-29 for me). Getting 27-28 on the highway is very tough for me, unless it's very level or a lot of gradual down hills, I'd have to keep it steady under 65.
To get home (on my normal commute), there is a final stretch of 9 miles starting from 520 ft to 2000 ft all straight up without dipping down. I was under the assumption I'd "get it back" on my way down the opposite way the next morning but that is not the case. The battery only charges to a certain point, then, the rest of the regen energy is not captured.
this explains the reason why I got such good mileage driving at 75 mph on the highway - Los Angeles to San Diego highway miles are all flat - pretty much close to the beaches - read: sea level. So, even though the published reports don't say as much as about mpg in hilly driving, I can say confidently that elevation change has more to do with MPG than simply categorizing your mpg by highway or local driving.
04-03-17, 01:39 PM
#964
Lexus Champion
I finally figured out what makes my HW and Local dirving MPG numbers look all funky. As it turns out it's the elevation change that is causing the most of my problem. Recently, I stayed at a location that is about the same as my work address elevation. Sure, there were some rolling hills and such but it wasn't as drastic as my daily commute. I recorded 28 mpg. that's like 15 to 20% difference from what I usually get.
To get home (on my normal commute), there is a final stretch of 9 miles starting from 520 ft to 2000 ft all straight up without dipping down. I was under the assumption I'd "get it back" on my way down the opposite way the next morning but that is not the case. The battery only charges to a certain point, then, the rest of the regen energy is not captured.
this explains the reason why I got such good mileage driving at 75 mph on the highway - Los Angeles to San Diego highway miles are all flat - pretty much close to the beaches - read: sea level. So, even though the published reports don't say as much as about mpg in hilly driving, I can say confidently that elevation change has more to do with MPG than simply categorizing your mpg by highway or local driving.
To get home (on my normal commute), there is a final stretch of 9 miles starting from 520 ft to 2000 ft all straight up without dipping down. I was under the assumption I'd "get it back" on my way down the opposite way the next morning but that is not the case. The battery only charges to a certain point, then, the rest of the regen energy is not captured.
this explains the reason why I got such good mileage driving at 75 mph on the highway - Los Angeles to San Diego highway miles are all flat - pretty much close to the beaches - read: sea level. So, even though the published reports don't say as much as about mpg in hilly driving, I can say confidently that elevation change has more to do with MPG than simply categorizing your mpg by highway or local driving.
saving there. Now it is spring weather which improves MPG making a difference.
04-03-17, 08:59 PM
#965
Driver School Candidate
I believe winter mileage is also reduced due to the winter gasoline blend. In Oregon, my 2016 RX450h and 2010 Prius MPG drops 3-6 mpg. I believe the refiners change to summer blend in early April, so I'm expecting mpg will go back up on my next fill up. The Prius has already increased 3-4 mpg over the course of 200 miles since its last fill last week.
04-06-17, 10:12 AM
#966
Instructor
something else I learned today regarding MPG and altitude.
for every 1000ft in elevation change (higher), the compression rate drops by about 3.5%. For places like Denver this means about 19% loss in compression; thus, the current 450H compression would go from 12.5 to 10.1, which is about the same as the regular RX350 engine (10.5) that requires only 87 octane gas. (higher compression engines require higher octane gas, generally speaking, you want the combustion to happen just a bit slower as the pistons squeeze harder and extract the last bit of torque)
even for my elevation (2000 ft) this would mean about 7% loss of compression and corresponding loss of torque - which also means that I'm pressing the gas pedal harder to make up for the loss...... this almost makes me want to use mid-grade gas since I may not be taking advantage of the full compression ratio anyway.......
should have bought a house by the beach.....
for every 1000ft in elevation change (higher), the compression rate drops by about 3.5%. For places like Denver this means about 19% loss in compression; thus, the current 450H compression would go from 12.5 to 10.1, which is about the same as the regular RX350 engine (10.5) that requires only 87 octane gas. (higher compression engines require higher octane gas, generally speaking, you want the combustion to happen just a bit slower as the pistons squeeze harder and extract the last bit of torque)
even for my elevation (2000 ft) this would mean about 7% loss of compression and corresponding loss of torque - which also means that I'm pressing the gas pedal harder to make up for the loss...... this almost makes me want to use mid-grade gas since I may not be taking advantage of the full compression ratio anyway.......
should have bought a house by the beach.....
04-07-17, 03:49 AM
#967
Lead Lap
Before electronically managed Fuel-Injected engines the air:fuel delivered by carbureted engines compounded the altitudinal pressure challenges.
Super/Turbo-charging successfully addresses both - while flattening the torque curve and increasing efficiency.
Super/Turbo-charging successfully addresses both - while flattening the torque curve and increasing efficiency.
05-24-17, 12:54 PM
#968
Instructor
something else I learned today regarding MPG and altitude.
for every 1000ft in elevation change (higher), the compression rate drops by about 3.5%. For places like Denver this means about 19% loss in compression; thus, the current 450H compression would go from 12.5 to 10.1, which is about the same as the regular RX350 engine (10.5) that requires only 87 octane gas. (higher compression engines require higher octane gas, generally speaking, you want the combustion to happen just a bit slower as the pistons squeeze harder and extract the last bit of torque)
even for my elevation (2000 ft) this would mean about 7% loss of compression and corresponding loss of torque - which also means that I'm pressing the gas pedal harder to make up for the loss...... this almost makes me want to use mid-grade gas since I may not be taking advantage of the full compression ratio anyway.......
should have bought a house by the beach.....
for every 1000ft in elevation change (higher), the compression rate drops by about 3.5%. For places like Denver this means about 19% loss in compression; thus, the current 450H compression would go from 12.5 to 10.1, which is about the same as the regular RX350 engine (10.5) that requires only 87 octane gas. (higher compression engines require higher octane gas, generally speaking, you want the combustion to happen just a bit slower as the pistons squeeze harder and extract the last bit of torque)
even for my elevation (2000 ft) this would mean about 7% loss of compression and corresponding loss of torque - which also means that I'm pressing the gas pedal harder to make up for the loss...... this almost makes me want to use mid-grade gas since I may not be taking advantage of the full compression ratio anyway.......
should have bought a house by the beach.....
05-24-17, 09:44 PM
#969
I followed up on my own question and used 89 gas for three tanks. The result was, well, not impressive. The mpg pretty much remained the same. However, my butt dynometer tells me I was short on top-end power. it was probably a bad idea using an 89 gas on a 12.5 compression engine anyway. Going back to using 91 octane.....
05-26-17, 12:19 PM
#970
Instructor
Easy way to tell. Do a couple of 0 to 60 runs. Because we have a hybrid (no brake torquing is needed), it's just a matter of jamming the accelerator and using an iPhone timer. You have to run it in opposite direction and average the two.
05-31-17, 04:30 PM
#971
Atkinson Cycle Engine
The engine of the Lexus 450h works on the Atkinson Cycle and not the Auto Cycle. The 13 to 1 compression is the max compression achievable. The compression is variable and controlled by the computer based on fuel grade, air density and air temperature. That is why the engine works equally well at 5000 feet as it does at sea level and works with fuel grades from 87 to 130 non leaded avgas. Unless you are drag racing your RX 450h, you will not notice the difference in performance only in your wallet. At 700 ft, I get an average of 33.3 mpg of Summer blend 87 octane around town and 30+ on the interstate. Winter drops to 28 and 29 due to engine heat up running the engine when the power is not needed.. What is important is using Top Tear brands since they do not foul the valves.
05-31-17, 05:26 PM
#972
Lexus Champion
Auto cycle = Otto cycle? Atkinson engine is good match for the hybrid to make up the low end torque. Actually hybrid will win the race against RX350.
Hybrid gets instant torque boost when pedal is punched. Goodness of electric motor. In my case I just drive like any other vehicle. Winter time 10liter/100Km,
summer time 7 liter/100Km. I always fill with Shell gas.
Hybrid gets instant torque boost when pedal is punched. Goodness of electric motor. In my case I just drive like any other vehicle. Winter time 10liter/100Km,
summer time 7 liter/100Km. I always fill with Shell gas.
Last edited by Htony; 06-01-17 at 06:17 AM.
05-31-17, 08:52 PM
#973
The engine of the Lexus 450h works on the Atkinson Cycle and not the Auto Cycle. The 13 to 1 compression is the max compression achievable. The compression is variable and controlled by the computer based on fuel grade, air density and air temperature. That is why the engine works equally well at 5000 feet as it does at sea level and works with fuel grades from 87 to 130 non leaded avgas. Unless you are drag racing your RX 450h, you will not notice the difference in performance only in your wallet. At 700 ft, I get an average of 33.3 mpg of Summer blend 87 octane around town and 30+ on the interstate. Winter drops to 28 and 29 due to engine heat up running the engine when the power is not needed.. What is important is using Top Tear brands since they do not foul the valves.
06-01-17, 03:20 AM
#974
Pole Position
http://www.toptiergas.com/licensedbrands/
06-01-17, 04:05 PM
#975
Driver School Candidate
29.8 mpg with 95% city driving, speeds between 25-45, trips between 3-7 miles each way. I also live at 5600 ft in an area with many hills and not too much traffic. I also work hard at getting good mileage by using pulse and glide where I accelerate up to 40 mph and coast back down to 33 mph then rinse and repeat. This works well in light to no traffic, but could get you shot in heavy big city traffic.
I also use 87 octane exclusively due to the elevation and have never experienced any knocking or performance issues. If I were to take the vehicle to a lower elevation I would likely increase the octane.
This technique has proven successful with many previous hybrids that I have owned (2003 Honda Insight, 2010 Honda CRZ) and my current 2011 RX 450H. If I drive on the highway the mileage really suffers back to around 25 mpg.
I also use 87 octane exclusively due to the elevation and have never experienced any knocking or performance issues. If I were to take the vehicle to a lower elevation I would likely increase the octane.
This technique has proven successful with many previous hybrids that I have owned (2003 Honda Insight, 2010 Honda CRZ) and my current 2011 RX 450H. If I drive on the highway the mileage really suffers back to around 25 mpg.