Premium Fuel Recommended

[lexus114]

Originally Posted By: delta901
I have a 01 ES300 with the same engine with OP's RX300 -> 1MZ-FE and can tell the diff. b/w regular v.s. prem.

If I switch instantly from a tank of 87 to 91, I won't feel much of a diff unless I reset your ECU (by pulling EFI fuse.) ECU must re-learn this new gas. However, if I switch instantly from 91 to 87, I will feel power loss.

Gas mileage up about ~5-7% if I up premium instead of regular and reset ECU. This was over 5 tanks of premium fuel. I also notice that prem give more benefit in hotter days that colder days so I use regular in winter (CA here) and use premium in summer.


finally,some one else that notices a difference!! i thought i stood alone.

 

[lexus114]

Originally Posted By: Char Baby
Originally Posted By: delta901
I have a 01 ES300 with the same engine with OP's RX300 -> 1MZ-FE and can tell the diff. b/w regular v.s. prem.

If I switch instantly from a tank of 87 to 91, I won't feel much of a diff unless I reset your ECU (by pulling EFI fuse.) ECU must re-learn this new gas. However, if I switch instantly from 91 to 87, I will feel power loss.

Gas mileage up about ~5-7% if I up premium instead of regular and reset ECU. This was over 5 tanks of premium fuel. I also notice that prem give more benefit in hotter days that colder days so I use regular in winter (CA here) and use premium in summer.


delta,
Does the ECU need to be reset or will it just take longer for it to learn and adjust for the difference in the higher octane?



if you want a more rapid response,reset ecm.

 

[kschachn]

Your RX 300 uses the same engine as my 1st-gen Sienna, the 3.0L 1MZ-FE, right? If so, that is a 10.5:1 compression ratio engine. Then there you have it as to why the higher octane is recommended. 10.5:1 is a pretty high compression ratio these days. All your engine is going to do with the lower octane is to retard the timing, along with all the negative benefits that brings.

 

[lexus114]

Originally Posted By: kschachn
Your RX 300 uses the same engine as my 1st-gen Sienna, the 3.0L 1MZ-FE, right? If so, that is a 10.5:1 compression ratio engine. Then there you have it as to why the higher octane is recommended. 10.5:1 is a pretty high compression ratio these days. All your engine is going to do with the lower octane is to retard the timing, along with all the negative benefits that brings.


yeah i thought about that compression ratio.it is pretty high for a street motor.factory motor anyway.

 

[Falcon_LS]

Interesting about the compression ratio. What would be considered "high" these days that would require higher octane fuel?

 

[lexus114]

well,i had a 2003 chevy cavalier with the 2.2 ecotec motor in the family.i was surprised to find out that it had a 10:1 compression,and still only required 87 octane.on the other hand,i believe anything over a 10.5:1 will require at least an 89 octane to perform to its full potential.(btw)the cavalier ran better on the 89 octane.

 

[mpvue]

back in the day, people thought anything over 8.5:1 would require high octane. these days, technology and combustion chanber design have allowed the use of higher compression and lower octanes. the computer can adjust mixture and ignition in an instant to account for load.
I remember reading that cadillac had to redesign the northstar for regular, because the 'typical' cadillac custome rwouldn't put up w/ having to use premium.
the CEO of my company has an acura TL that he runs on regular. he's just cheap.
I had a '94 mazda 626 V6 that required 91 or higher. what a PITA; it only had 162hp! to make it worse, it only managed 25mpg hwy! a much better car was my '02 saturn L200; 2.2 ecotec, 140hp, regular gas, 34mpg.

 

[BuickGN]

Originally Posted By: mpvue
back in the day, people thought anything over 8.5:1 would require high octane. these days, technology and combustion chanber design have allowed the use of higher compression and lower octanes. the computer can adjust mixture and ignition in an instant to account for load.
I remember reading that cadillac had to redesign the northstar for regular, because the 'typical' cadillac custome rwouldn't put up w/ having to use premium.
the CEO of my company has an acura TL that he runs on regular. he's just cheap.
I had a '94 mazda 626 V6 that required 91 or higher. what a PITA; it only had 162hp! to make it worse, it only managed 25mpg hwy! a much better car was my '02 saturn L200; 2.2 ecotec, 140hp, regular gas, 34mpg.


That's crazy considering the 04-08 TL runs an 11.0:1 compression ratio. We still have people putting 87 octane in them, saving money at the pump only to get a drop of 5+mpg due to timing retard. In this car, it costs more money to run regular, not to mention power and the negatives associated with retarded timing.

 

[Falcon_LS]

Some very interesting info here! Just happen to find out the compression ratio on my Montero is 9.0:1, but I run 87 AKI (91 RON). Would there be any benefit to running 91 AKI (or 95 RON)?

 

[rg200amp]

Originally Posted By: Falcon_LS
Some very interesting info here! Just happen to find out the compression ratio on my Montero is 9.0:1, but I run 87 AKI (91 RON). Would there be any benefit to running 91 AKI (or 95 RON)?


Use whats spec'd. That will work best.

 

[BuickGN]

Originally Posted By: Falcon_LS
Some very interesting info here! Just happen to find out the compression ratio on my Montero is 9.0:1, but I run 87 AKI (91 RON). Would there be any benefit to running 91 AKI (or 95 RON)?


If it pings on the current gas you will see a benefit from higher octane. If it doesn't ping, there will be no gains from higher octane.

 

[labman]

Originally Posted By: Falcon_LS
Some very interesting info here! Just happen to find out the compression ratio on my Montero is 9.0:1, but I run 87 AKI (91 RON). Would there be any benefit to running 91 AKI (or 95 RON)?


One way higher compression engines cope with lower octane gas is to retard the spark. Modern engines have a knock sensor and dial the timing back if it knocks before you ever hear the first ping. So using a higher octane gas may give better performance. When our 92 Grand Am with the HO Quad 4 was new, I played around with premium and regular. I never though I saw much difference. My teenage son claimed he could. After trading it in an 02 Cavalier with an Ecotec, I have stuck to regular. Both were 5 speeds. Catching a lower gear also allows faster timing without pinging. You might see more difference with the conservative shift points automatics use now.

 

[Falcon_LS]

I experimented with higher octane fuel (91 AKI) this time round, and there's been quite some improvement over 87. When I first started her up in the morning, the engine would bog down upon shifting into drive with the 87. That doesn't happen anymore with 91. Performance wise, the engine feels a tad more responsive. To top it up, there also seems to be an improvement in fuel economy, but I will need to wait until my next fill up to confirm.

 

[crinkles]

would an engine with VVT-i adjust for higher octane?? owner's manual says 91 RON (regular) or higher. (doesn't say any more)

 

[Falcon_LS]

Back when I had my Outlander (Mitsubishi 4B12 2.4L engine with VVT), the only improvement I noticed with 95 RON was slightly better fuel economy. But was less than 0.5 km/L, so I continued using 91 for cost reasons. Owner's manual also recommended 91 RON or higher. Not sure about the Toyota 2.4 though.

 

[lexus114]

Originally Posted By: Falcon_LS
Back when I had my Outlander (Mitsubishi 4B12 2.4L engine with VVT), the only improvement I noticed with 95 RON was slightly better fuel economy. But was less than 0.5 km/L, so I continued using 91 for cost reasons. Owner's manual also recommended 91 RON or higher. Not sure about the Toyota 2.4 though.


i notice a big difference in performance,and almost a 1 mpg more in millage.

 

[Peter_Pan]

Originally Posted By: crinkles
would an engine with VVT-i adjust for higher octane?? owner's manual says 91 RON (regular) or higher. (doesn't say any more)


VVTI has nothing to do with detecting fuel grades. All modern fuel injected cars will instantly detect the octane and adjust timing to avoid pings. If your manual recommends a certain octane and you put higher octane in it you're just wasting your $ as your engine lacks the compression it needs to get the most out of higher octane gasoline.

 

[lexus114]

+++++ "1" ^^^^

 

[BuickGN]

Originally Posted By: Peter_Pan
Originally Posted By: crinkles
would an engine with VVT-i adjust for higher octane?? owner's manual says 91 RON (regular) or higher. (doesn't say any more)


VVTI has nothing to do with detecting fuel grades. All modern fuel injected cars will instantly detect the octane and adjust timing to avoid pings. If your manual recommends a certain octane and you put higher octane in it you're just wasting your $ as your engine lacks the compression it needs to get the most out of higher octane gasoline.


Modern cars don't detect octane, they detect pinging. The sensor is reactive meaning it has to ping before the computer can adjust timing and even then it puts full timing back in usually within a second of pulling it out. It's much safer than the old days without a knock sensor but you don't want to rely on the sensor, you need enough octane. Besides, once detonation starts, you have to pull more timing to stop it than if it didn't start in the first place.

 

[Peter_Pan]

Originally Posted By: BuickGN

Modern cars don't detect octane, they detect pinging. The sensor is reactive meaning it has to ping before the computer can adjust timing and even then it puts full timing back in usually within a second of pulling it out. It's much safer than the old days without a knock sensor but you don't want to rely on the sensor, you need enough octane. Besides, once detonation starts, you have to pull more timing to stop it than if it didn't start in the first place.


Correct, my response was poorly worded perhaps. As you say the pinging, knocking and timing retardation all occurs near instantly. So the process is repeated constantly till the knock goes away presumably by user putting the minimum recommended octane. I exclusively run Shell V-Power in my Merc and consistantly get higher MPGs (both manually calculated and through the on board computer) compared to EPA numbers so at least I know it's recovering part of the extra cost by going further.