89 Vs 91 Octane

[pchrist]

Can anyone tell me if i will see an increase in MPG's if i would switch? Going to run an experiment with my next tank and see. Anyone have any insight on what i could expect? Also will i need to be just about empty or would a quarter tank mixed in be bad? Do the positives, if any, make up for the price difference??

 

Can't wait to hear the responses

 

Pete

[gvbhunt]

Unless your timing tables have been modified for the higher octane, you will not really notice anything. If your engine is prone to spark knock that will go away though...

[HawkeyeOC]

I would guess that it will take a few tankfulls for the computer to adjust to the 91 octane. If there was a noticeable mileage difference, manufacturers would be recommending it big time.

 

Probably a waste of money unless yout truck hates the cheaper stuff and I have had a few of those throughout the years...mostly Fords!

[z85violator]

im doing the same thing right now. im on my first tank of 89 from switching up from 87. so far it seems to be able to hold a certain speed going up a certain hill without the tranny having to downshift.im going to run it for 5 tanks and see, minimul cost difference to me and if the truck runs better and see slightly more kms per tank ill stay with it.

[marko]

I have a 91 octane superchips tune. 91 octane costs about 7% more than 87 up here.

 

I drove 100km, or 60 miles of highway driving home today, at about 60-65 mph. Not much wind, a bit here and there.

 

I reset the fuel economy at the start of the trip. At the end of the trip I checked the DIC. Average fuel economy 11.7L/100km. Or, in American, 20.0 mpg! And that's US gallons. Note that my truck is a 2005, and does not have DOD/AFM.

 

I used to own a 71 ford with a 390. It ran better on premium, and got 15% better mileage on premium.

 

Just my $0.02,

[silversport]

only if your vehicle can benefit from the octane change...higher octane gives your truck the ability to resist spark knock better...if you don't get spark knock at 87...why would you change?...furthermore...some vehicles actually run worse on higher octane...again,...why do it???...your computer will adjust almost immediately...no need to wait a couple of tankfuls...good luck.

[a_guerrajr]

how can you tell if you have spark knocK??? NEWB

[C & A s Dad]

I will share my experience. I have read several threads on this on multiple forums and there are opinions all over the board. I have come to accept what I have read from some respected ASE Certified techs and what I have experienced.

 

Your computer will adjust but it does take at least 2 to 3 tanks for it to become fully adjusted. Besides, you cannot judge MPG by comparing 1 or 2 tanks. Most modern engines like the 5.3 are fairly high compression engines by today's standards (9:1 to 9.5:1) and they would never run without severe detonation (ping)on 87 if it were not for the assistance of the knock sensors and the computer.

 

Just in case you are unfamiliar with what the system does: As soon as a knock sensor detects detonation it sends a message to the comp to reduce timing to stop the ping and this also reduces power. This happens in a nano second. The comp then slowly begins adding timing back until the sensor detects detonaiton again and guess what, it pull timing back again to compensate. This cycle happens over and over.

 

With 91 or as I run 93, the detonation either will not happen at all or it at least will allow for more timing to be run which allows more power.

 

I run 93 in my Yuk XL 5.3 because I tow a 6500 lb camper on occasion and there is no doubt my truck pulls hills better on 93. I also run an Interceptor scan gauge to monitor trans temps and it will also show ignition advance and timing retard. I have tried to make the PCM retard the timing and only one time at wide open throttle I saw it remove 4 degrees for less than 2 seconds. Plain and simple, the 93 octane will allow much more timing to be run without ping which will give you a slight power gain.

 

Did it help my MPG? A little. Using a 6 tank avg on 87 I got 18.19 MPG. I then ran 7 tanks on 93 and my avg was 18.42. Not a big change.

 

I tried running 93 in my Caravan I use for work and saw absolutely no difference in perf or MPG. Of course the compression ratio on the little 3.3 is approx 8:1. No need for any more octane.

 

Sorry for the long post but this is as close to the facts about 87 vs 91 or 93 that I have been able to gather.

[silversport]

spark knock will be the pinging/knocking noise you hear and it is most often bad...good luck with what you choose...having higher octane will only advance the timing as far as the designer of the computer allows...sometimes the computer cannot take advantage of the higher octane...that was my point...if it works for you...more power to you...

Bill

[C & A s Dad]

Bill, you are correct in saying that the higher octane will only allow the timing to advance to the point the engineers designed the system. However, this point is still higher than if the system was running on 87 octane. You are also correct about detonation being a bad thing. You never want to run an engine with detonation, this is why the knock sensors are there so the computer can pull timing back and stop the ping.

[fbachman]

spark knock will be the pinging/knocking noise you hear and it is most often bad...Bill

 

 

Problem is, you won't hear it much anymore. The ECM will detect the knock so readily, as the sensors are so sensitive anymore, and add knock retard in the timing that you won't hear it unless it's aggregious.

 

Best way to tell is to have a way to monitor knock retard, and adjust timing such that you get NONE (KR) at WOT.

[RVJ]

Where I live, the 89 octane is 10% Ethanol and the 87 octane is not. Although the octane rating is higher with ethanol the mpg's for me was less so there was no payoff. The ethanol seemed to run hotter in my Motorcycle also so I don't buy it anymore for either vehicle.

[mi.bowtie]

Don't waste your time or money

[57loboy]

I've been playing with my Superchips Flashpaq for a while with a couple of other mods already installed: Corsa cat-back, K&N FIPK. I saw a 1.5-2 mpg increase in average fuel economy on over 10k miles of driving on the 91 octane performance tune (I do about 2500-3000 miles a month). When I did the mathemagic to calculate the ROI on the fuel economy versus the higher cost of premium, I still made out ok, not by much, but it worked out ok.

I've since ditched the K&N FIPK as the drone on the highway was driving me nuts and when I put the stock boomerang mess back on, I noticed a drop in power and economy. I've just put an Airaid Jr setup on that uses the stock airbox but replaces the messy factory intake tube. After 40 miles on that, there's a big improvement in off the line responsiveness. Too soon to tell where the economy will end up.

[need-for-speed]

The most important factor is what does the owner's manual recommend? Any higher octane that what is reccomended by the engineers that designed it - is a waste of money. The only exceptions would be if you had a tune which inclued a more agressive spark curve, or as another member suggested - pulling a heavy load. Otherwise, save your money and only buy what is in the owners manual.

 

Contrary to popular belief, higher octane fuels do not have a higher energy/lb content. Higher octane fuels do a better job of resisting knock and that is all they do.

 

For my Corvette, I burn premium, because that is what it says to burn in the owners manual. For our 2005 Tahoe, we burn regular unleaded, because that is what the owner's manual recommends, and it does not knock. One exception, is that at higher altitudes, an engine's octane requirements go down. But basically, if 87 octane regular unleaded works ar seal level, then 85 octane regular unleaded will work in the mountains. Same thing for 93 octane super uleaded at sea level vs. 91 octane super at 5000 ft MSL.

 

The problem with trying to gauge it with MPG is that - if you want to get better MPG, you probably will, because subconsciously, you will go easier on the throttle, and therefore - get better mpg.

 

Save your money, and only buy what it says to buy in the owners manual.