Premium - 40 cents per gallon more than regular
11-09-14, 06:31 AM
#31
Alrighty. There's a lot of wondering in this thread and that shouldn't be the case. An answer exists and it's that:
87 octane is safe for our cars. But not optimal for power or fuel economy.
My rule of thumb is that I use 89 octane unless premium is within 15 cents a gallon, and as long as 89 octane is within 20 cents a gallon of 87 octane.
Basically, an engine's octane requirement is a function of its compression ratio and its ignition timing.
Ignition timing was the starting point of electronic engine control, and Japan has forgotten more about electronic engine controls than the rest of the world has learned. Our ECUs estimate fuel quality a few hundred times a second and use the information to adjust the ignition timing and camshaft phasing on the fly to achieve optimal combustion. They can absolutely handle 87 octane.
Around the world, fuel economy varies radically. And Toyota makes sure that the engine won't grenade if you run a few gallons of 83 octane "gas" through it. Obviously that fuel isn't ideal though.
Secondly, our engines do have a modestly high compression ratio at 10.5:1. Mazda runs 13.1:1 compression ratios on 86/87 octane. The ratio of 10.5:1 won't perform optimally on 87 octane (89 octane is basically the minimum for excellent combustion performance at the 10.5:1 ratio) but they can hack it. And it becomes even easier on the engines when the ignition is adjusted for the fuel quality.
In my experience, I've found that 91 octane gets about 15% better mileage than 87 octane, and 89 octane gets ~10% better milage. So the question you should be asking is "which is the most cost effective?"
If you really wanted, you could go find 94 octane or 101 octane, and pay $10/gallon to test it out. You'll find our engines don't do much with the extra octane.
The compression ratios and electronic controls that make our engines work with 87 octane don't lend themselves to high performance on abnormally high octane gases. You'll notice more of a difference going from 87 to 89 octane than 89 to 91 octane. And you probably won't notice a difference between 91 and 93, and there will be no difference, or even a decline in performance from 93 octane to 100+ octane.
At some point, our engines can't squish the fuel and air mixture more, and can't advance the ignition any more, and can't make more power. And that's probably at 93 octane.
I have a 125cc Honda Grom with an 8.7:1 compression ratio. Its top speed is about 60 mph when I run 87 octane. If I run 93 octane, it only goes about 57 mph.
How could that be?
Well, it can squish the 87 octane fuel air mixture really well and ignite it just after the piston moves to top dead center. Higher octanes resist detonation and the spark plug has to fire well before the piston reaches the top to make sure the flame spreads throughout the cylinder. This reduces the capacity for power and drops the efficiency of the engine.
87 octane is safe for our cars. But not optimal for power or fuel economy.
My rule of thumb is that I use 89 octane unless premium is within 15 cents a gallon, and as long as 89 octane is within 20 cents a gallon of 87 octane.
Basically, an engine's octane requirement is a function of its compression ratio and its ignition timing.
Ignition timing was the starting point of electronic engine control, and Japan has forgotten more about electronic engine controls than the rest of the world has learned. Our ECUs estimate fuel quality a few hundred times a second and use the information to adjust the ignition timing and camshaft phasing on the fly to achieve optimal combustion. They can absolutely handle 87 octane.
Around the world, fuel economy varies radically. And Toyota makes sure that the engine won't grenade if you run a few gallons of 83 octane "gas" through it. Obviously that fuel isn't ideal though.
Secondly, our engines do have a modestly high compression ratio at 10.5:1. Mazda runs 13.1:1 compression ratios on 86/87 octane. The ratio of 10.5:1 won't perform optimally on 87 octane (89 octane is basically the minimum for excellent combustion performance at the 10.5:1 ratio) but they can hack it. And it becomes even easier on the engines when the ignition is adjusted for the fuel quality.
In my experience, I've found that 91 octane gets about 15% better mileage than 87 octane, and 89 octane gets ~10% better milage. So the question you should be asking is "which is the most cost effective?"
If you really wanted, you could go find 94 octane or 101 octane, and pay $10/gallon to test it out. You'll find our engines don't do much with the extra octane.
The compression ratios and electronic controls that make our engines work with 87 octane don't lend themselves to high performance on abnormally high octane gases. You'll notice more of a difference going from 87 to 89 octane than 89 to 91 octane. And you probably won't notice a difference between 91 and 93, and there will be no difference, or even a decline in performance from 93 octane to 100+ octane.
At some point, our engines can't squish the fuel and air mixture more, and can't advance the ignition any more, and can't make more power. And that's probably at 93 octane.
I have a 125cc Honda Grom with an 8.7:1 compression ratio. Its top speed is about 60 mph when I run 87 octane. If I run 93 octane, it only goes about 57 mph.
How could that be?
Well, it can squish the 87 octane fuel air mixture really well and ignite it just after the piston moves to top dead center. Higher octanes resist detonation and the spark plug has to fire well before the piston reaches the top to make sure the flame spreads throughout the cylinder. This reduces the capacity for power and drops the efficiency of the engine.
11-09-14, 06:53 AM
#32
I consistently get better mileage running 93 over running 87. More efficiency inherently means better mileage under the same load. If you have a heavy right foot that is another case. I get about 2 or 3 more mpg on 93.
Last edited by Lavrishevo; 11-09-14 at 04:03 PM.
11-10-14, 08:41 AM
#34
I the last 4 years and 10 months I have always used regular 87 octane in my LS430. I have burned 5,083 gallons. Gas was 20 cents more for premium but somewhere along the way the vendors figured they could increase the upcharge to 40 cents. Even if I average the two, at 30 cents multiplied by 5,083 I have saved $1,525 in 5 years. For my family buget this is not chump change! As an experiment I used premium 91 octane for 4 fill-ups and saw no change in MPG. However I knew when I bought the car it would be nice to drive and more expensive to own and operate than other options, I just choose to not use premium fuel and I drive like there is an egg unger my gas pedal.
11-10-14, 10:08 AM
#35
Racer
I'd guess no one who posts in this CL forum drives their LS hard in a city. I don't and couldn't even if I wanted to ! I drive easy because I enjoy driving easy. Its saves in many ways, gas + brakes + speeding tickets + reduces accidents.
I still use 91 because once in a while I do wide open accelerate my LS. I hit the gas at between 40 and 50 mp.h. entering a quiet country highway, or down some straight empty 4 lane highway. I get to XXX mph and coast back down to the speed limit. I'll drive speed limit for a while and maybe, if I feel like it, I do it again LOL. After 4 years it still impresses me ! Ya, it uses more gas and the event doesn't last a long time - but it makes me smile. It's worth $300 a year to me.
At least once a year I turn the traction control off and do a "donut" or 2 in a snow covered parking lot .
Before I get flamed be aware I have been driving over 40 years, have a clean driving record with no moving violations and have never hit anyone or anything with any car.
11-10-14, 05:07 PM
#36
My LS unequivocally does NOT get better mileage on 91 octane over 87 octane (we only have 87, 89 and 91 available in CA). I am a stickler for recording every drop of gas that went in my car and how many miles I got out of those drops. 91 does NOT equal better MPG. Maybe 93 does.
11-10-14, 05:16 PM
#37
The best mileage I have ever seen was running a tank of 93 plus a bottle of Lucas upper engine treatment. I don't know what kind of driving you do but it's mostly highway for me. This is where I see the difference. In the city there is no difference. Try it sometime. 91 plus a bottle of octane boost.
Also. What kind of mileage are you getting? This was freeway average mileage for 16 miles home.
Also. What kind of mileage are you getting? This was freeway average mileage for 16 miles home.
Last edited by Lavrishevo; 11-14-14 at 08:06 AM.
11-12-14, 09:36 AM
#38
Pole Position
The best mileage I have ever seen was running a tank of 93 plus a bottle of Lucas upper engine treatment. I don't know what kind of driving you do but it's mostly highway for me. This is where I see the difference. In the city there is no difdernce. Try it sometime. 91 plus a bottle of octane boost.
Also. What kind of mileage are you getting? This was freeway average mileage for 16 miles home.
Also. What kind of mileage are you getting? This was freeway average mileage for 16 miles home.
Seriously, what were the driving conditions? What was your average speed for the 16 miles of "freeway"? (Of course, 16 miles is an extremely small sample size.) I have average 26 - 27+ MPG over several hundred miles with A/C compressor off, cool/cold outside air conditions, little headwinds, average speed about 75 mph and 87 Octane gas, which is what I've run for 230K+ miles on my '01 (5-speed).
11-12-14, 09:45 AM
#39
Racer
exactly ...... downhill with a tail wind. The roof antenna is too small for a sail !
11-12-14, 03:59 PM
#40
I can easily return 25 MPG on the highway over hundreds of miles if I'm driving at or under the speed limit, using 87 octane gasoline. 31.4 MPG (as shown in that photo) is possible but you'd have to be hypermiling the car or going downhill. I occasionally put in high octane gas if I anticipate going up mountain passes in very hot weather (and even then it's most likely not even close to 'necessary') otherwise 87 all the way.
Since every piece of data I have on my car says that 91 octane makes no difference in MPG and I don't care that my car is 0.2 seconds slower in the quarter mile I'll continue with 87. Now where's that emoticon of a smilie-face beating a dead horse?!
11-14-14, 08:11 AM
#41
So, no hyper milling, and not driving 17 mph.
This was my trip home from Union City to Atlanta on I85. Anyway, the roads are not downhill nor are they particularly flat. Anyone who knows the Atlanta area can testify to this. Of course, weather conditions play a roll as always but I can consistently get great mileage if I keep the speeds down. This was averaging between 60 and 70 mph. Once you hit 75 - 80 and up the mileage drops by at much as 4 mpg. Of course a strong headwind will kill mileage as well. I also attribute getting great MPG to a clean MAF and throttle body, new plugs, running synthetic oil, and riding great Michelin tires inflated properly. All this stuff helps in the long run.
https://www.clublexus.com/forums/ls4...great-mpg.html
This was my trip home from Union City to Atlanta on I85. Anyway, the roads are not downhill nor are they particularly flat. Anyone who knows the Atlanta area can testify to this. Of course, weather conditions play a roll as always but I can consistently get great mileage if I keep the speeds down. This was averaging between 60 and 70 mph. Once you hit 75 - 80 and up the mileage drops by at much as 4 mpg. Of course a strong headwind will kill mileage as well. I also attribute getting great MPG to a clean MAF and throttle body, new plugs, running synthetic oil, and riding great Michelin tires inflated properly. All this stuff helps in the long run.
https://www.clublexus.com/forums/ls4...great-mpg.html
Last edited by Lavrishevo; 11-14-14 at 08:16 AM.
03-27-21, 09:34 AM
#42
premium car, so premium gas
The LS series cars are Japan's top of the line cars, so why would you not use premium gas for what it was designed for? I have two, 1991 Lexus Ls400's with close to 600,000 kilometers on one and 460,000 on the other, and I never had to change any O2 sensors, knock sensors, or any other sensors (no check engine lights). I am still on the original exhaust system. Seems to me LS cars love premium fuel. For those that aren't going to keep their cars very long, I guess it does not matter. I now have a 2002 LS430 Custom Luxury (88,000 miles) that I am working on (new shocks, door lock motors, timing belt etc., little things that need attention) , I will be using premium fuel in it. I want as few problems down the road as possible. Love these cars!!
03-29-21, 03:45 AM
#43
Instructor
Lexus recommend using 91PON (US) and above so use that.
Here in the UK I use 95RON = 91PON but that is our lowest octane gas anyways.
We also have "Super" that is 97RON to 99RON but you'll gain nothing from using it other than a lighter wallet.
Just because the marketing people call it Premium doesn't make it superior at anything other than allowing higher compression ratios. :-)
As for comparing the 400 and the 430, you are comparing a fully stainless steel exhaust (400) vs a stainless & mild steel exhaust (430), comparing different O2 sensors, and the 430 has VVT which the 400s didn't get until 1997.
Here in the UK I use 95RON = 91PON but that is our lowest octane gas anyways.
We also have "Super" that is 97RON to 99RON but you'll gain nothing from using it other than a lighter wallet.
Just because the marketing people call it Premium doesn't make it superior at anything other than allowing higher compression ratios. :-)
As for comparing the 400 and the 430, you are comparing a fully stainless steel exhaust (400) vs a stainless & mild steel exhaust (430), comparing different O2 sensors, and the 430 has VVT which the 400s didn't get until 1997.
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