V8 Drivers Regular or Premium?

[t4r_se_n_wv]

Last weekend I thought I would give regular gas (87) a try. Well to my disappointment on that tank of gas I got 14.8 mpg (with the majority highway). Usually on a tank of Premium (93) I get on avg. about 16.5-17 mpg. My question is has any other V8 driver used regualr and seen these kind of results? And should I just stick with Premium (long term effect)? What do you other V8 drivers use?

 

[jpalaska]

A friend of mine who is a petroleum engineer and a car nut told me 87 octane should be fine, but maybe fill up with 90 octane every 4th or 5th tank.
I've been getting around 16.5 mpg in mostly city driving with the A/C turned off.

JP

 

[greasefingers]

My v8 has never seen anything other than regular gasoline. I get 16 to 18 mpg calculated(city driving)

 

[TheBlueWave]

A V6 driver here, but in this blistering cold weather I get poor mileage no matter what. I have noticed, however, that my mileage is slighly higher when using the premium fuel. It is not enough to offset the 20 cents extra cost. Here in Iowa where I'm assigned for work, 89 octane fuel is the cheapest (10% subsidized ethanol) so I use that. Just my v6 $0.02.

 

[mole177]

primo for me.. always have and always will

 

[Vino]

Ever since last November my mileage went down, like many of us know over the years winter gas is garbage.
Anyway, 87 worked in my car but 91 has been fantastic, especially the colder it gets.

The Runner is averaging about 16.8 MPG all city driving, 18 mpg in the summer, 06 V8 SE.

I also use FP60 at almost every fill up from lube control.

 

[ProMed]

87 only for me. I have only had my 06 T4R for 6 days, but my 01 Tundra also had the 4.7 V8 that I put 120,000 miles on. If I ever experienced pre-ignition or spark knock then I would have changed to primo but imo it is not needed if that's not the case.

 

[TRZ06]

Call me crazy, and some will dispute this, but I CAN feel a performance difference with 91 compared to 87.

The engine is a little more peppy and responsive. It's not a huge jump by any means, but my SOTP says it is there.

As far as gas mileage, that is hard to say, because you never have the exact same throttle position and other factors such as wind speed, asends, descends, engine fuel management, OAT etc. as a constant. Just a 1/16 difference in throttle position means a difference in MPG, it may not yield a noticable difference in acceleration but it will affect overall MPG.

 

[jwyshrek]

the 4.7V8 will make a little bit more horsepower with the higher octane gas...it can advance the timing a little more than with 87 or lower octane.

 

[ProMed]

the 4.7V8 will make a little bit more horsepower with the higher octane gas...it can advance the timing a little more than with 87 or lower octane.

How does that work? The lower octane gas is able to ignite at a lower flash point than the higher octane, hence the need to run higher octane gas in a vehicle with a high compression engine to prevent pre-ignition. How would the 4.7 V8 know to advance the timing when running premium fuel?

 

[greasefingers]

The two knock sensors will detect pre-ignition if too low of an octane is used. I have no idea what too low is 87or 89? If pinging is detected by the sensors then the ECU will retard the timing by an amount so that no pre-ignition is current. It does this instantly and before one can detect or hear it ping.

Old school method was: use the lowest octane until pinging is heard and then use the next higher octane amount. This is not a valid method for engines with knock/accelerometer sensors. The correction to maintain correct air-to-fuel ratio, is too fast.

How much performance is lost if the engine timing is constantly retarded???

 

[jwyshrek]

Probably need to get someone to do a dyno run...87 vs. 91/93.

I remember a while back...reading or watching something about the Acura TL...said something about getting an extra 5-10 hp with premium gas...???

 

[ProMed]

The two knock sensors will detect pre-ignition if too low of an octane is used. I have no idea what too low is 87or 89? If pinging is detected by the sensors then the ECU will retard the timing by an amount so that no pre-ignition is current. It does this instantly and before one can detect or hear it ping.

Interesting, thanks!

 

[Casper]

most modern cars these days have knock sensors and as such can detect just how well combustion is taking place through your 02 sensors and make ignition advance/retard changes.

I have no doubt that the 2uz can make more power on higher octane fuel the question comes with that, is just how much. I have run unleaded 100octane in mine and seen that its much more responsive and seems to make more power across the entire rev band. The question is really whats availible to you in your area? Here in Vegas and across most of the west, all we get is shitty 91 octane, the 4pts really isnt going to make to large of a difference. Those of you where 93 is avail could see larger performance.

The issue that comes into play is that normally higher octane burns slower and needs a higher compression ratio to take advantage of this point. I would think that 91/93 is the highest that the 4runner would normally take....though after running 100 in it, it seems like it likes that alot too.

 

[HiVel-JR]

If I could find some 100+ octane I would run a couple of tanks just for fun.

I bought my 4runner in Arizona and the highest octane there was 91. I did not see 93 octane until I got near Dallas. I ran the 91 in both my wifes car (VW passout) and the 4runner. Her car suffered from the change (93 to 91) and I could feel it. Once we got east of the Mississippi River we started running 93 octane again and I noticed the difference in both vehicels. It is a slight difference, but I could notice it. The vehicles were a little more responsive.

One interesting fact. After running 93 octane in my wife's car for over 4 years and switching to (forced to 91) the car developed emissions problems with the engine and the computer. There was build up in the engine, but VW fixed the issue by cleaning out the engine. (not sure what VW did, but they had to take the engine apart and clean it out.)

So I try to run the highest octane I can with out switching to lower octanes unless I have to.

 

[khaug]

On 87 octane regular, our '03 V8 will run noticably rough under moderate acceleration, This is the knock sensors intervening and dialing back the ignition timing. 89 octane mid-grade reduces this somewhat, but it's still detectable. 91 (or better) octane premium completely eliminates the roughness, and the engine becomes smooth as butter.

It's pretty clear the engine's ecu is mapped for premium fuel, but will permit the use of 87 or 89 if you're not bothered by the mild rough running under load. I run premium when towing and mid-grade the rest of the time. Does this give me better mpg? Probably, but I'd be hard-pressed to say it's enough of a payback to justify it strictly on a dollar basis.

 

[greasefingers]

I have never experienced rough running on regular gas or I would switch grades. I am very concerned about performance and maintenance.

I highly doubt that one should be able to tell the difference between regular & premium gasoline. I guess I will have to try it. My 2003 v8 is at a 9,6:1 compression ratio. This would not warrant 91 octane in IMO. My Volvo has a 10.5:1 CR and will not run correctly on regular. The newer VVT engine has a higher CR and may very well require something higher.

If the engine was designed for of 91 octane then anything higher would seen to be wasteful and certainly a disadvantage, as now it would appear that engine may advance the timing to compensate for the harder to burn fuel. I do not know enough about this subject as I am not a chemical engineer.

 

[JoJoBetsy]

I've never run anything but 87 regular and I'll average 16-18 mpg as a daily driver and 13 as a tower. I've pulled the 5000lb+ boat around without a single performance issue; sometimes flooring it and never a stutter. Regular in Austin is $1.96 at Costco today and Premium is $2.36.

 

[Northof49]

I ran 3 V8's, two 05's and an 03 on almost nothing but 87 and never had any issues or rough running. Towing, elevation, etc....no problems at all, good mileage, good power.

Gotta remember that switching back and forth will do you no good.....pick an octane and stick with it, as the computer will "learn" and map for the best performance vs fuel used.

As for using 93 or above....you might as well light your money on fire, as all you're doing is accomplishing that + excess heat. The best performance is attained at the minimum octane needed for 0 detonation. Running 100 octane in your 4Runner would be an expensive way to go slower....

 

[blindside]

On 87 octane regular, our '03 V8 will run noticably rough under moderate acceleration, This is the knock sensors intervening and dialing back the ignition timing. 89 octane mid-grade reduces this somewhat, but it's still detectable. 91 (or better) octane premium completely eliminates the roughness, and the engine becomes smooth as butter.

It's pretty clear the engine's ecu is mapped for premium fuel, but will permit the use of 87 or 89 if you're not bothered by the mild rough running under load. I run premium when towing and mid-grade the rest of the time. Does this give me better mpg? Probably, but I'd be hard-pressed to say it's enough of a payback to justify it strictly on a dollar basis.

:rocker: i agree with you, even though i have a V6