Regular Gas (350) vs. Premium (450h)??
03-16-18, 02:51 PM
#1
Intermediate
Thread Starter
Regular Gas (350) vs. Premium (450h)??
I am confused by this chart on the Lexus site. It shows the Hybrid requiring Premium when the RX 350 only calls for Regular.
Most of the Hybrids run on Regular while the normally aspirated gas counterparts run on Premium???
Is the Chart wrong? Do you need to run Premium in the RX 450h ?
https://lexus2.custhelp.com/app/answ...xus-vehicle%3F
Most of the Hybrids run on Regular while the normally aspirated gas counterparts run on Premium???
Is the Chart wrong? Do you need to run Premium in the RX 450h ?
https://lexus2.custhelp.com/app/answ...xus-vehicle%3F
03-16-18, 09:04 PM
#2
Intermediate
The gasoline engine on the RX450h uses a Miller cycle combustion process whilst the RX350 is the traditional Otto cycle. Hence the different engine code RX450h - 2GR-FXE and RX350 - 2GR-FE.
Whilst there are knock sensors on both engines to retard the ignition advance to avoid pinging, allowing for regular unleaded to be used in the 2GR-FXE engine really softens the torque deliver to the point where I prefer to drive in Sport Mode. With premium fuel, after some time, the ignition advance adapts to the higher octane fuel and I can feel better engine response return to the point where I don't desire to drive in Sport Mode but am happy with the default Normal Mode.
I'm also conscious that the 2GR-FXE motor has EGR whereas the 2GR-FE does not. Verified by comparing the intake manifolds on my vehicle vs my BIL's. There is no EGR for the RX350.
Now I don't know what the long term effect is of introducing spent exhaust gases back into the intake manifold, but I do know that the higher octane fuel will probably burn cleaner because the higher energy content of the fuel means less fuel is required for the same amount of output from the engine. Less fuel = less soot = less crap/soot being recycled back through the intake manifold is, Remember the intake manifold is where hot engine oil vapours are being drawn in from the engine via the PCV - hot oily vapours in the intake manifold isn't an issue but when there is EGR soot in there as well, a cruddy messy buildup will begin to form on the inlet manifold. Not good.
As any owner of a modern common rail turbo diesel engine with Euro 4 or higher compliance - horror stories abound of black gunky buildup in the inlet manifold.
Fortunately this is less of an issue with the 2GR-FXE engine because the manifold has to come out entirely for the 100,000 mile spark plug replacement job, so it's possible to clean it up.
Anyways, premium unleaded for my RX450h - mainly for better throttle response (ergo more enjoyable driving experience) and that's what Lexus recommends. I don't see the point of using cheaper gasoline when the cost of fuel savings pales into insignificance compared to the depreciation of the vehicle. Might as well as get the most satisfaction out of the time I spend having to drive the vehicle, that's my thinking.
Whilst there are knock sensors on both engines to retard the ignition advance to avoid pinging, allowing for regular unleaded to be used in the 2GR-FXE engine really softens the torque deliver to the point where I prefer to drive in Sport Mode. With premium fuel, after some time, the ignition advance adapts to the higher octane fuel and I can feel better engine response return to the point where I don't desire to drive in Sport Mode but am happy with the default Normal Mode.
I'm also conscious that the 2GR-FXE motor has EGR whereas the 2GR-FE does not. Verified by comparing the intake manifolds on my vehicle vs my BIL's. There is no EGR for the RX350.
Now I don't know what the long term effect is of introducing spent exhaust gases back into the intake manifold, but I do know that the higher octane fuel will probably burn cleaner because the higher energy content of the fuel means less fuel is required for the same amount of output from the engine. Less fuel = less soot = less crap/soot being recycled back through the intake manifold is, Remember the intake manifold is where hot engine oil vapours are being drawn in from the engine via the PCV - hot oily vapours in the intake manifold isn't an issue but when there is EGR soot in there as well, a cruddy messy buildup will begin to form on the inlet manifold. Not good.
As any owner of a modern common rail turbo diesel engine with Euro 4 or higher compliance - horror stories abound of black gunky buildup in the inlet manifold.
Fortunately this is less of an issue with the 2GR-FXE engine because the manifold has to come out entirely for the 100,000 mile spark plug replacement job, so it's possible to clean it up.
Anyways, premium unleaded for my RX450h - mainly for better throttle response (ergo more enjoyable driving experience) and that's what Lexus recommends. I don't see the point of using cheaper gasoline when the cost of fuel savings pales into insignificance compared to the depreciation of the vehicle. Might as well as get the most satisfaction out of the time I spend having to drive the vehicle, that's my thinking.
03-17-18, 10:07 AM
#3
The 450h motor is an Atkinson cycle, not Miller or Otto. An Otto cycle is what most engines are. The Miller cycle effectively lengthens the compression stroke by leaving the intake valve open longer and generates more power, but requires forced induction. An Atkinson cycle lengthens the power stroke to extract more energy from the combustion for better efficiency at the expense of torque (although I'm not exactly sure on what the Toyota implementation of this is.)
My theory on this, and this is just my theory, is in the hybrid there is more than just the relationship of the engine powering the wheels. The engine output is not always directly related to what is being sent to move the vehicle. My best guess on this is there are situations where the 450h will need more power than a 350, i.e. move/accelerate the thing at the same rate as a 350 and charge the battery, which would require the motor to produce more power and require the higher octane fuel. This would be an engineering decision since in reality they could have just adjusted the power split but you would loose some power for acceleration and divert it to the traction battery.
There may be some tuning in the ECU where premium helps with efficiency but higher octane is generally for more power, although the engineers may have figure out some run profiles that would require premium for less than peak power but higher efficiency.
For the most part modern ECUs have gotten so good at tuning things on they fly that most will not notice the difference between premium and regular since we usually don't demand maximum power in daily driving. Of course this depends on what the maximum rated power for the motor is.
My theory on this, and this is just my theory, is in the hybrid there is more than just the relationship of the engine powering the wheels. The engine output is not always directly related to what is being sent to move the vehicle. My best guess on this is there are situations where the 450h will need more power than a 350, i.e. move/accelerate the thing at the same rate as a 350 and charge the battery, which would require the motor to produce more power and require the higher octane fuel. This would be an engineering decision since in reality they could have just adjusted the power split but you would loose some power for acceleration and divert it to the traction battery.
There may be some tuning in the ECU where premium helps with efficiency but higher octane is generally for more power, although the engineers may have figure out some run profiles that would require premium for less than peak power but higher efficiency.
For the most part modern ECUs have gotten so good at tuning things on they fly that most will not notice the difference between premium and regular since we usually don't demand maximum power in daily driving. Of course this depends on what the maximum rated power for the motor is.
03-17-18, 11:30 AM
#4
My take is that a Miller engine is the same thing as an Atkinson engine, only with a supercharger.
In a conventional Otto-cycle engine, about 1/3 of the energy of combustion goes out the tailpipe as waste heat, 1/3 of the energy goes into the cooling system and out the radiator as waste heat, and 1/3 goes into moving the car. The Otto engine gets energy by taking in a fuel charge, compressing it (perhaps 10:1), igniting the vapor, and using the greatly-increased pressure to force down the piston and opening up the exhaust valve. The compression ratio is the same as the expansion ratio.
One major way of increasing the efficiency of an engine is to significantly increase the expansion ratio, so that by the time the exhaust valve opens there is not much pressure left in the chamber. But in the Otto engine that would also increase the compression ratio, and there comes a point where the fuel mixture won't be stable at such high pressures. So the Atkinson engine keeps the intake valve open longer than usual during the compression phase so some of the mixture squirts back out into the intake manifold. Then combustion and a high expansion ratio. From what I gather they get about 5% more efficiency this way.
You get more efficiency but less power, since less fuel has been used. But the hybrid doesn't care, since it has a big electric motor to help shoulder the load under those circumstances. So the best of both worlds.
As for premium versus regular, look at these boards. A common topic and probably thousands of comments pro and con. I suspect most of us use regular, since it appears to make very little difference. But use what you wish.
In a conventional Otto-cycle engine, about 1/3 of the energy of combustion goes out the tailpipe as waste heat, 1/3 of the energy goes into the cooling system and out the radiator as waste heat, and 1/3 goes into moving the car. The Otto engine gets energy by taking in a fuel charge, compressing it (perhaps 10:1), igniting the vapor, and using the greatly-increased pressure to force down the piston and opening up the exhaust valve. The compression ratio is the same as the expansion ratio.
One major way of increasing the efficiency of an engine is to significantly increase the expansion ratio, so that by the time the exhaust valve opens there is not much pressure left in the chamber. But in the Otto engine that would also increase the compression ratio, and there comes a point where the fuel mixture won't be stable at such high pressures. So the Atkinson engine keeps the intake valve open longer than usual during the compression phase so some of the mixture squirts back out into the intake manifold. Then combustion and a high expansion ratio. From what I gather they get about 5% more efficiency this way.
You get more efficiency but less power, since less fuel has been used. But the hybrid doesn't care, since it has a big electric motor to help shoulder the load under those circumstances. So the best of both worlds.
As for premium versus regular, look at these boards. A common topic and probably thousands of comments pro and con. I suspect most of us use regular, since it appears to make very little difference. But use what you wish.
03-17-18, 02:58 PM
#5
Intermediate
Yep RX450h is Atkinson cycle, not Miller cycle. My bad. I was thinking of a Mazda engine which has Miller cycle. Atkinson cycle, as mentioned above, similar to Miller cycle, sans forced induction.
Anyway the point being is that it's not a traditional Otto cycle and therefore not surprising that Lexus recommends a different fuel, possibly to take advantage of the more complete combustion of the fuel.
There are heaps of existing threads on this forum, so if you search for it, you'll see numerous responses on this forum.
Anyway the point being is that it's not a traditional Otto cycle and therefore not surprising that Lexus recommends a different fuel, possibly to take advantage of the more complete combustion of the fuel.
There are heaps of existing threads on this forum, so if you search for it, you'll see numerous responses on this forum.
Last edited by tempestv8; 03-17-18 at 03:29 PM.
03-17-18, 04:06 PM
#6
Instructor
can you explain this a little more? I thought you just pull the spark plugs and replace with new ones. But what's up with the manifold???
03-18-18, 02:35 AM
#7
Intermediate
Trending Topics
03-18-18, 07:42 AM
#8
Hybrids are claimed to be Atkinson but mechanically they are not. Atkinson engine has additional components that those engines do not have. You can look up Atkinson engine schematics online and see for yourself.
What they did for hybrids, they faked Atkinson cycle through VVT-I operation.
Hence, it is Atkinson-like engine.
Another thing they did - thank you, Toyota(sarcasm) - they reduced engine power output. I am guessing, to compensate for additional power and torque from motor generator. Otherwise, it'd have been heck of powerful engine, but a bit lesser mpg.
That in mind, I am simply guessing that as the result, they allowed those to run on lower grade fuel.
Regular Lexus rx350 engine has minuscule power advantage over Highlander engine yet, is told to be run on 91 or higher octane or Armageddon will come. Word out is that, as specs are technically same, extra 5hp is accomplished by software, not mechanical trickery. Higher octane then is good for the big oil and keeps wolves happy.
Below are opinions that vary on the subject:You've provided some very good information here (i.e., that the Highlander engine is a doppelganger for the RX engine). You'll hear from some that you are doing horrible things to your engine running 87 octane; why would you risk expensive damage just to save 20 cents a gallon?; etc. etc. yada yada yada.Your logic is correct; virtually the same powerplant tuned to make slightly more power output if you run higher octane fuel. Who wants to spend thousands more for a Lexus and have it reported that it is only as powerful as it's Toyota brethren?I've run 87 octane in three RXs now for well more than 100k miles (some miles at wide open throttle right up to redline) and never heard a ping, a knock, a bang, etc.; every owners manual recommended 91 octane or better (but how much better? - I can get my hands on 112 - should I run this instead?) And I've always been pretty impressed at the power output - never a sign of compromise from my vantage point. The 2010 engine is very impressive.My opinion: high octane and 5 horsepower is just marketing BS. The owner's manual does not "prohibit" you from running 87 octane; only recommends high octane to obtain best performance.
I just checked at Motor Trend specs. for the 2009 Highlander and the 2009 RX350
Same motor designation 2GR-FE
Same compression ratio: 10.8
3,456 cc
Toyota: Power: 201 kW , 270 HP SAE @ 6,200 rpm; 248 ft lb , 336 Nm @ 4,700 rpm
Lexus: Power: 201 kW , 270 HP SAE @ 6,200 rpm; 251 ft lb , 340 Nm @ 4,700 rpm
It may be that the Lexus has a slightly more aggressive timing or camshaft (or not) but the specs are so similar (max. power and torque at same RPMs) that I don't see that there really is a need for premium fuel for the one and not for the other.As a first step, I will try using 89 octane fuel (mid-grade here in Miami) instead of premium 93.
This above brings to a question. How is it that engine with same compression ratio requires higher octane fuel? Should it have been higher ration, then yes, higher octane is less prone to ping. But same?
What they did for hybrids, they faked Atkinson cycle through VVT-I operation.
Hence, it is Atkinson-like engine.
Another thing they did - thank you, Toyota(sarcasm) - they reduced engine power output. I am guessing, to compensate for additional power and torque from motor generator. Otherwise, it'd have been heck of powerful engine, but a bit lesser mpg.
That in mind, I am simply guessing that as the result, they allowed those to run on lower grade fuel.
Regular Lexus rx350 engine has minuscule power advantage over Highlander engine yet, is told to be run on 91 or higher octane or Armageddon will come. Word out is that, as specs are technically same, extra 5hp is accomplished by software, not mechanical trickery. Higher octane then is good for the big oil and keeps wolves happy.
Below are opinions that vary on the subject:You've provided some very good information here (i.e., that the Highlander engine is a doppelganger for the RX engine). You'll hear from some that you are doing horrible things to your engine running 87 octane; why would you risk expensive damage just to save 20 cents a gallon?; etc. etc. yada yada yada.Your logic is correct; virtually the same powerplant tuned to make slightly more power output if you run higher octane fuel. Who wants to spend thousands more for a Lexus and have it reported that it is only as powerful as it's Toyota brethren?I've run 87 octane in three RXs now for well more than 100k miles (some miles at wide open throttle right up to redline) and never heard a ping, a knock, a bang, etc.; every owners manual recommended 91 octane or better (but how much better? - I can get my hands on 112 - should I run this instead?) And I've always been pretty impressed at the power output - never a sign of compromise from my vantage point. The 2010 engine is very impressive.My opinion: high octane and 5 horsepower is just marketing BS. The owner's manual does not "prohibit" you from running 87 octane; only recommends high octane to obtain best performance.
I just checked at Motor Trend specs. for the 2009 Highlander and the 2009 RX350
Same motor designation 2GR-FE
Same compression ratio: 10.8
3,456 cc
Toyota: Power: 201 kW , 270 HP SAE @ 6,200 rpm; 248 ft lb , 336 Nm @ 4,700 rpm
Lexus: Power: 201 kW , 270 HP SAE @ 6,200 rpm; 251 ft lb , 340 Nm @ 4,700 rpm
It may be that the Lexus has a slightly more aggressive timing or camshaft (or not) but the specs are so similar (max. power and torque at same RPMs) that I don't see that there really is a need for premium fuel for the one and not for the other.As a first step, I will try using 89 octane fuel (mid-grade here in Miami) instead of premium 93.
This above brings to a question. How is it that engine with same compression ratio requires higher octane fuel? Should it have been higher ration, then yes, higher octane is less prone to ping. But same?
2018 Toyota Highlander and 2017 Lexus RX Specifications
Model Year20182017ModelToyota HighlanderLexus RXEngine3.5L V6 Hybrid
DOHC-4v
257 hp@257
245 lb-ft@48003.5L V6 Hybrid
DOHC-4v
259 hp@6000
247 lb-ft@4800
TWO hp difference? TWO torques?
DOHC-4v
257 hp@257
245 lb-ft@48003.5L V6 Hybrid
DOHC-4v
259 hp@6000
247 lb-ft@4800
03-18-18, 07:29 PM
#9
Intermediate
Found this chart from Lexus:
https://lexus2.custhelp.com/app/answ...xus-vehicle%3F
What's interesting is that for the RX350, for MY2011, 91 is recommended but from MY2012 onwards, 87 is recommended.
For the RX450h, it is 91 octane all the way.
https://lexus2.custhelp.com/app/answ...xus-vehicle%3F
What's interesting is that for the RX350, for MY2011, 91 is recommended but from MY2012 onwards, 87 is recommended.
For the RX450h, it is 91 octane all the way.
03-19-18, 03:37 AM
#10
Pole Position
This is probably the most heated debate on these forums. Do whatever makes you comfortable. I use 87 octane in our 2015 RX450h. Experimenting with the other two levels, I have noticed zero difference in gas mileage or performance. I have used 87 in cars that have required premium for over a million miles and have not had one problem.
I always revert back to two MIT graduates that are car mechanics who had a syndicated radio show called Car Talk for 35 years.
http://www.cartalk.com/content/premi...egular-0#myth4
From the USA Today:
The only modern engines that should really need premium are those with superchargers, which force-feed fuel into the cylinders. "You're driving along and just tramp the gas and the knock sensor cannot sense the knock fast enough in some cases," because the supercharger boosts pressure so fast, says Bob Furey, chemist and fuels specialist at General Motors.
Burning regular when the owner's manual specifies premium won't void the warranty, nor damage the engine, even the most finicky automakers say. "You're giving up perhaps just a little bit of performance that a customer wouldn't really even notice, it's so slight," says Furey.
All this being said to each his own.
I always revert back to two MIT graduates that are car mechanics who had a syndicated radio show called Car Talk for 35 years.
http://www.cartalk.com/content/premi...egular-0#myth4
From the USA Today:
The only modern engines that should really need premium are those with superchargers, which force-feed fuel into the cylinders. "You're driving along and just tramp the gas and the knock sensor cannot sense the knock fast enough in some cases," because the supercharger boosts pressure so fast, says Bob Furey, chemist and fuels specialist at General Motors.
Burning regular when the owner's manual specifies premium won't void the warranty, nor damage the engine, even the most finicky automakers say. "You're giving up perhaps just a little bit of performance that a customer wouldn't really even notice, it's so slight," says Furey.
All this being said to each his own.
03-19-18, 08:13 PM
#11
Driver
Found this chart from Lexus:
https://lexus2.custhelp.com/app/answ...xus-vehicle%3F
What's interesting is that for the RX350, for MY2011, 91 is recommended but from MY2012 onwards, 87 is recommended.
For the RX450h, it is 91 octane all the way.
https://lexus2.custhelp.com/app/answ...xus-vehicle%3F
What's interesting is that for the RX350, for MY2011, 91 is recommended but from MY2012 onwards, 87 is recommended.
For the RX450h, it is 91 octane all the way.
Not sure why the hybrid takes premium. Probably something something 0.2% better thermal efficiency.
03-25-18, 07:11 AM
#12
Lexus Test Driver
Join Date: Aug 2007
Location: Western Australia (Australia)
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Down here in Australia "regular gas" is 91 octane and premium is 95. The fuel cap (and car manual) advise 95 octane. It seems that the US gas is 4 Ron (Octane) lower than our petrol. Did note however that the RX is compliant with 10% ethanol
03-25-18, 04:01 PM
#13
Intermediate
I think it takes a while for the RX450h to re acclimatize to the higher octane fuel. In my 3rd tank of 98 octane RON (Australian), which is even higher than the 95 or the 91 octane that we get Down Under, my Fuelly app says that I've got my best fuel consumption ever. I do realise that I've spent unnecessarily more money by putting in in fuel that's even higher than the recommended 95 octane, but it was just an experiment to see what the effect is. Another interesting observation is that the low rev droning at around the 1200 RPM mark is far more refined with the higher octane fuel. Not sure whether this coincided with the engine readjusting to the higher octane fuel but it's clear to me something has changed, for the better. For the small additional cost of the higher octane fuel, it's what I'm prepared to fill my vehicle with as the additional refinement is quite tangible to me once the engine had adjusted to the premium fuel.
06-15-18, 05:47 AM
#14
Rxh premium gas vs Rx regular gas?
i just confirmed for myself something i had no idea existed. While reading a post i noticed someone brushed over the fact that hybrids( '14s at least) still require,suggest, premium gas while the regular 350's are on regular gas.Seems odd to me, since i thought they both had the same block/base engine. Can anyone clarify for me? Thanks.
06-15-18, 07:10 AM
#15
Moderator
Been covered a few times. In the end it really makes no difference which gas you use.