Yes, I'm noticing it also. I ran 87 first 2 tanks, 89 next 2 tanks, and now on 93 for first tank . I'm seeing the mpg difference here in FL.

 

Have you two felt any power increase?
The camaro forums have been all over the place when it comes to octane. Same lfx engine.

 

Has the weather remained constant there? Here in Michigan it was in the 20's on Saturday and 40's on Sunday which would make a significant improvement despite the gas.

 

Soul i can feel a little bit of difference with having increased power but where i can really feel the biggest difference is with how much more responsive the truck is when you just lightly hit the gas. Before I had to really push the pedal to get the truck to go, but now it barely takes any effort at all and feels like a normal truck.

 

Thanks for the reply. I find this interesting but not unheard of. 11.5:1 compression should like higher octane. Direct injection lets us get away with 87. I will try on my next fill up and see what happens. I am curious more than anything.

 

Kingdom

Yesterday was in the mid 20's while I was driving. I let my last tank run almost completly empty before filling with 93 and i noticed the difference immediately after filling up.

 

This engine is not optimized for 93 Octane fuel. The 40 cents more per gallon you are paying will not be offset by any mpg gain if any. I work in the medical field. Sometimes a medication is given to a patient even though the doctor knows that it will not make a bit of difference but the patient thinks they are getting a miracle cure. They would have gotten well just as fast without the medicine. This is called the placebo effect. Putting 93 octane in this engine without a tune for 93 octane is a waste of good money. Spend your hard earned cash on other toys for your truck or get a tune that is designed to burn 93 octane.

 

I'll agree. The data supports 87 in a modern DI engine in terms of power/mileage. A subjective report of 100 miles in unknown variable conditions is not enough data points to make a decision at this time. There are A LOT of scientific studies on this subject in modern engines, check out the Federal Trade Commission for example.

 

Jeffdawg i understand what you are saying but how do you then expalin the gain in 1.5mpg between city and highway? I am not trying to start a pissing match here by any means but based off of the trucks computer that is the increase i am seeing. I put another 50 miles on the truck today which where all city and I am still sitting at 18.6 mpg compared to the 17 I was getting with 89 octane. I am also driving the same roads for my commute everyday as well.

 

I noticed today on a decent highway trip I was averaging about 21 mpg at 78mph, compared to about 19 or 20mpg last week. The difference was today it wasn't a blizzard, and we actually hit 42 degrees for the first time this year. I wish I could pump some more sunshine at the pumps. Still can't believe we are still having discussions about how premium gas somehow creates a bunch of great effects on our vehicles. Even if it were true, it isn't worth it unless the vehicle is designed for it. I wonder how much of this really is the "miracle cure".

 

I wonder how much of this really is the "miracle cure".

It's like those stories you read on the internet where a person has cancer, then drinks some herbal drink one night and 6 months later the cancer is gone. It MUST be the herb, there's no other explanation! lol.

 

Has it gotten warmer in your area? I see a jump of 2mpg or more when it gets above freezing, FWIW. Went from upper 17's to around 20 mpg for my "last 50 miles," average when the temps went from 20's to around 40 'round here.

Or maybe the improved throttle response you mentioned means you aren't having to get into the accelerator as much and that's improved your average?

Just thinking out loud. I may try a tank of premium sometime out of curiosity as well. I'm too cheap to use it long term if I don't have to, tho! B-)

 

Has it gotten warmer in your area? I see a jump of 2mpg or more when it gets above freezing, FWIW. Went from upper 17's to around 20 mpg for my "last 50 miles," average when the temps went from 20's to around 40 'round here.

For years I've been thinking the colder the air is going in, the greater the power and efficiency of the burn. Help me out here - what did I miss?

 

If an ECM on a direct injection engine see's changes in the burn quality by using 93 vs 87 it will change the injection timing accordingly. Not sure if the ECM on the colorados/canyons are doing this but I dont see why it wouldnt. In the manual it suggests using 87 or greater octane. If you have a more complete burn with a higher octane fuel the injectors will have to supply less fuel, thus an increase in mileage/power.

 

Your premise is based in fallacy. The ECM does not detect "burn quality" other than through the spark knock sensor, misfiring, and O2 content. 93 octane (in an engine not tuned for it) has a poorer "burn quality" as it is not as volatile, and burns more slowly, than 87 octane. It does not produce any more BTUs (power) than 87. It only inhibits pre-detonation due to being less volatile. It is a myth higher octane, by itself, produces more power. Do the research and you will find this is fact, not fiction.

 

Anyone who says a modern high compression engine doesn't/can't benefit from higher octane gas without an aftermarket tune doesn't understand how things work these days.

Stock engines have many calibrations it can use, if the knock sensor isn't being tripped it will advance the timing until it senses knock. Using higher octane gas will allow the engine to advance timing to the max possible on the stock tune, so you may get a bit more power than is ever possible with regular 87 octane.

Just because a modern engine can run 87 octane doesn't mean it runs its best on it.

 

Ah-------------some one that understands knock sensors, and how the engine computers tries to optimize power and mileage.

 

The gains from running Super on a modern engine can be quite pronounced for the average driver. But I have essentially given up trying to convince people of this.

Sometimes mileage gains can be hard to document but it isn't for me as I'm always within a few tenths every single tank. Many drivers try to measure mpg gains on a very steady flat easy highway cruise because it's so repeatable. The problem with this technique is that this is a very low load situation and therefore the engine might not have to retard the ignition timing to prevent detonation so you might see no difference under these particular circumstances. I will often buy a grade of fuel lower if I'm on a long road trip on a cool day because the Octane isn't as important.

Even my '09 Canyon sees notable improvements in mpg with changing Octane. But it's not quite enough gain in mpg (about 1.5mpg or 8%) to offset the increased cost (about 16% currently) so if ALL you care about is the lowest fuel cost per mile driven, you are likely better off buying the lowest grade.

For me, I prefer the additional performance and range more than I prefer the extra few cents in my pocket.

 

You might see some little gain. My point was that it is not worth the extra cost for 93 octane. The extra $$$ you are paying will not be matched by mpg gains. Maybe if you get a good tune, but then if you look at the cost of the tune and the cost of gas it probably still is not worth it. I have been through all the trials and testing and using ethanol free vs 10% blend and using tier one gas vs supermarket gas etc. In the end, you come out ahead just using the 87 octane the truck is tuned for. I have other toys to spend my money on.

 

Just to clarify the engine is not "tuned for 87 Octane". It has a very conservative tune from the factory that can certainly utilize high octane fuel but as we see, they can still operate quite well on the lower octane fuel but it does so by retarding the ignition timing where the entire engine is less optimized. If the engine was truly 'tuned for 87 octane' it would run lower compression and run more advanced timing to get the best mpg on the low octane stuff. But they don't due it that way because the epa doesn't use 87 octane fuel to test with.

EPA mpg ratings are simply too important to forego a solid 1 mpg gain just by utilizing the EPA test fuel's high octane rating.

Otherwise, I agree with your post. Modifications are always fun but the common selling point of higher mpg can never make up for the additional cost of the mods themselves. But then, if your V6 now runs like a V8, would you have expected a V8 option to have payback in fuel costs? Probably not.

 

Correct and agreed. They aren't 'tuned' for 87. You have high and low octane tables. The biasing on low octane biases everything downward. Rather than keeping it there forever, using higher octane allows the ECM to bias everything upward.

In the end, it's all going to depend on the driving habits of the owner. MPG, fuel octane, and power discussions always puzzle me because not everyone drives the same, as you pointed out in one of your earlier posts.

Like you and others have said, newer electronics, fuel delivery systems, and manufacturer calibration strategies all support the fact that using higher octane is, essentially, better. It ultimately comes down to personal preference.

 

WOT-Tuning, you're what my Navy would call an SME (Subject Matter Expert). Always nice to have a couple of you folks on speed-dial.

I was getting a little lost in the vague reference to the "placebo effect" that higher octane might have on trucks and how that would increase MPG when there was no physical/chemical reason it should - like it's all in the truck's head. (?) Next thing you know, someone's gonna tell me - with a straight face - to take the truck to a therapist. Honestly, there are some things I am just not smart enough to understand. (Calm down y'all, just havin' fun - laughter's the best medicine. The laugh's actually on me. I talk to my truck. (Yes I do. Picture Robert Duvall in Days of Thunder.) Used to talk to my helicopters, too. And yes, it did work. (Trust me, I was there.) :neutral:

On a serious note W-T, do any of the octane booster products I can buy off the shelf do anything they claim on the label? (This is only the first of many questions I may pose to you.)

Cheers,
Scotty

 

Hey Scotty! We like to try and be as helpful as possible.

As was stated earlier, the reason you use higher octane rated fuel is to ward off knock. Think of it basically as a cooler burn/ignition keeping cylinder temps/pressure down. Because the higher octane is detected by the ECM, it starts using the high octane tables and changes the power delivery/knock strategy, which includes raising timing advance. a few more added degrees of timing at WOT is what helps make the extra HP/TQ. But, it also helps cruising at steady speeds allowing the engine to lean out the air/fuel mixture a tad, since there is less danger of knock. This increases fuel economy just a bit.

So, warding off knock with a higher octane rated fuel allows the engine to continue making power, safely.
Its all really going to depend on the driving habits of any given individual.

As far as the octane booster you can buy off the shelf, I consider it to be snake oil. The advertising of all the octane boosters on the market is that they raise the octane rating by X amount of points. Most consumers think that this means 1 whole point. So if you used 93 and buy octane booster that says it raises the level by 5 point, you think your ending up with 98 octane. The reality is that a point is actually measured as .05. So five of those .05 points adds up to .50. Effectively, you are only raising the rating in your tank by what we would consider half a point, to 93.5. Waste of money

 

Colder air is more dense which is good for hp. But it also causes more air resistance, lower tire pressures, and higher oil viscosity throughout the vehicle that take longer to come up to temperature. All of this ultimately reduces mpg.

 

You left out the most important factor. The denser air needs more fuel to maintain the proper air/fuel ratio, thereby decreasing fuel mileage.

 

Okay. Makes sense about the tires. And I know that temperature and humidity will affect ballistics tables, so that makes sense, too.

Is there enough difference in the viscosity of 5W-30 oil that you could see a measurable difference in HP, TQ, & MPG (without obscenely precise - and expensive - instrumentation; i.e. an electron microscope or a flux capacitor or something)? And wouldn't that difference last only as long as it takes the oil to reach normal operating temperature? I don't know about the oil - seems like a stretch. But I don't know.

Never really thought about these elements. At 20 degrees, I'm too worried about keeping my feet warm. Living in Florida has turned me into a wuss when it comes to cold weather.


Thanks.

 

Cold air is more dense. Denser air contains more oxygen. More oxygen per unit of air requires more gas to maintain same air fuel ratio by O2 sensor. Therefore, in the winter gas consumption will possibly go up. Conversely though, that extra gas/air is giving you better combustion therefore giving you more horsepower, so you should need less throttle to accelerate. It's all a big variable. Many other factors add or subtract from the equation. YRMV

 

I'm going to fill up with 93 next time and try a few tanks. I will gladly pay more for gas if it helps my Canyons performance. The way GM has this truck constantly searching for the right gear is quite annoying. As I have posted in other threads, I love everything about this truck. The ride, all of the electronics, the looks, the size, the autotrac, and it's very quiet. But quite honestly, my 2009 Tacoma and 2012 Colorado were more fun to drive. When I stepped on the gas, the response was immediate. I didn't have to wait for the transmission to catch up with the engine. I sure hope GM is listening and offers us owners a software upgrade. I'm not holding my breath.

 

Chrysler put a seminar on about 10 years ago about fuel burn, regular gas burns hotter then premium, that's from a room full of engineers.

​

 

You guys are confusing a lot of things and the some of the postings are filled with misinformation. The octane of a given fuel has NOTHING to do with the energy released when it is burned. Octane in non-scientific terms is the measurement of a given fuel's resistance to auto ignition. Higher octane fuel self ignites at a higher temperature. That temperature is reached by compressing the air on the compression stroke of the cylinder. One detrimental issue with the higher octane fuel is it's slower burn rate. For this reason we try to ignite it earlier in order to get it near maximum burn at just past top dead center of the power stroke.

Cold air helps get more oxygen into the cylinder with means more fuel can be introduced at WOT and more power can be developed. It also means there is more air to be compressed and a higher pre-ignition temperature inside the cylinder.

A detriment effect of cold air is it is more dense and it produces more drag on the body of the vehicle going down the road. One of the things most any pilot can tell you is it takes much less runway to get an airplane off the ground at 0 degrees than it takes at say 100 degrees. We have table for every aircraft and are suppose to calculate the effect of outside temperature prior to every take off.

Why is this? Because the engine can develop more power and the more dense air traveling across the wings develops more lift. Hense a shorter take off roll. Once off the ground the trick is to go high where that air is much thinner. Thinner air means less drag with more speed and better fuel economy. Have you ever wondered why commercial jet aircraft cruise up to the 40,000 feet range. The answer is much less drag and better fuel economy. The temperature is much colder but that is not a factor. They use an engine compressor stage to get enought air in to burn fuel at that altitude

Back to the gasoline powered engine. Since 87 octane burns quicker than 91 or 93 or 100LL, it will develop slightly more power because the piston is closer to Top Dead Center when most of the fuel is burned.

So it is a delicate balance of how soon to ignite the fuel to get the most power from without firing too soon to cause it to burn before TDC causing detonation or ignition ping. In a ground vehicle the air (and fuel) charge is seldom a full charge since we do not drive at WOT (Wide Open Throttle) continuously. With less than a full charge the mixture burns more slowly and more ignition advance can be tolerated.

Octane rating has little to do with power or mpg. As an example ethanol has a higher octane rating than gasoline but is has a lower btu per gallon rating than gasoline. So while it is higher octane it gets poorer mileage than straight gasoline.

If you want to dig into it further take a look here at the GGE (Gasoline Gallon Equivalent) tables for various fuels.

Gasoline gallon equivalent - Wikipedia, the free encyclopedia

I'll stay out of the fray, because these types of threads always bring out the urban legends, marketing hype, and the people that "know it all" about this stuff. I watched one thread go on for months on an "econo-box" forum that I watch. It got stretched into attributes of ethanol and "top tier" marketing of various brands of fuel.

Good luck on this discussion. Just do not read believe everything you read. Everyone is a expert on this subject.

Remember that they can not put anything on the Internet that isn't true.

 

91 octane


Thanks for the info. Don't know if I understand it all. I did get 30 miles per gallon on a trip a few days ago. I was using 91 octane. I'll try 87 for a couple tanks then see what i get.
Dennis

 

Hey n9cv. That was a good write up. If more people would just read it they maybe they could learn something.

 

I came from the turbo import world, I refuse to run 93 in a 4cyl truck!!

 

The problem with "I put in 93 octane and got X" is that even if you think you're not being affected by the placebo effect, you might be.

It's why when doctors do medical research, not even the doctor that is giving you a trial medicine knows whether or not you get the placebo or the test medication. It's called double blind and the only way to be 100% sure would be to have a group of people filling up every day on gas that they have no idea what it actually is, and to drive normally.

When you know you're trying to test your mileage you're going to drive different in subtle ways, the weather might be different, etc.

 

Or just observe the OEM fueling tables that increase timing when less detonation is detected and then apply basic knowledge about all engines...

It isn't rocket science.

I liked the Navy guy's comment some pages back about his truck needing therapy because it was all in the truck's head...lol. Well it is all in the truck's head if you consider the truck's head is it's computer that does in fact adjust the fuel mixture and timing based on detonation.