2015 Sierra 4.3 L and high octane fuel

[Txjose]

I understand that my engine may not have exactly 285 hp and a few hp up or down isn't going to change the functionality of my truck. My 4.3 V6 seems to be a little more lively using premium fuel. I suspect there is more to this than just a feeling. Adding a couple of horsepower with all other conditions being equal should translate to some changes in performance.

Changes in temperature often have more impact on an engines behavior then people give it credit for.

 

A good tune will wake up that 6er!!!

[Willshire]

Perhaps it is a case of less knock retard during wot with higher octane fuel as the knock sensors will detect less knock on premium gas

[Donstar]

Thanks for the comments. I must say I am not overly knowledgeable about engines. I love driving and having others do the fixing. My pickups of the 60's and 70's had carburetors fed by a fuel pump. I can understand how such a setup would not behave differently for changes in fuel content. I know carburetors could be adjusted or changed and different fuels could be accommodated. I am wondering if changes in technology is changing old understandings that suggest using higher octane fuel is wasted on an engine that burns regular. If a mass production engine can adjust for two extreme differences in fuel, (87 octane and E85) then what is stopping it from adjusting for everything in between?

[Willshire]

I was looking at PID's in my Autocal yesterday and GM actually has a sensor for checking alcohol percentage. Maybe that's how the truck knows its running E85

[Badass69]

Willshire, on 04 Jan 2016 - 09:49 AM, said:

I was looking at PID's in my Autocal yesterday and GM actually has a sensor for checking alcohol percentage. Maybe that's how the truck knows its running E85

 

That's exactly how it does it. You have two totally different tables for fuel and spark with E85 or regular gas. GM didn't "tune" the regular gasoline tables with premium fuel in mind so you will get the maximum spark advance the PCM can give for whatever situation and that's it... even though it's not detonating it will not go beyond that. E85 has a higher octane rating but also requires a lot more fuel for any given situation so they can safely advance the timing further without risk of knock..... Running premium may help a truck tuned for regular not knock under certain loads and so forth but you won't get the full benefit of the fuel without making changes to the settings.

[Donstar]

I was looking at PID's in my Autocal yesterday and GM actually has a sensor for checking alcohol percentage. Maybe that's how the truck knows its running E85

I am not aware of the use of Autocal however what you are saying makes sense. Most of the regular gas available has 5% ethanol and most of the e85 ethenol has 15% gasoline. When you switch between the two fuels you can end up with an almost endless variety of alcohol/gas combinations in your tank. Certainly it would not be a huge leap in logic to assume that performance will change based on the current mixture. It would not be a case of you getting either 285 hp (regular 87 octane) or 297hp (e85 105 octane). I believe that using increasingly higher octane rated gasolines will show proportionately improved performance.

[Willshire]

 

That's exactly how it does it. You have two totally different tables for fuel and spark with E85 or regular gas. GM didn't "tune" the regular gasoline tables with premium fuel in mind so you will get the maximum spark advance the PCM can give for whatever situation and that's it... even though it's not detonating it will not go beyond that. E85 has a higher octane rating but also requires a lot more fuel for any given situation so they can safely advance the timing further without risk of knock..... Running premium may help a truck tuned for regular not knock under certain loads and so forth but you won't get the full benefit of the fuel without making changes to the settings.

Agreed. If you see any kind of performance gain at all it will only be from WOT as the knock sensors will pick up less knock than on regular fuel and since knock retard isn't used that often, the benefits of premium over regular will be hardly noticed. Unless your WOT all the time lol

[Badass69]

I am not aware of the use of Autocal however what you are saying makes sense. Most of the regular gas available has 5% ethanol and most of the e85 ethenol has 15% gasoline. When you switch between the two fuels you can end up with an almost endless variety of alcohol/gas combinations in your tank. Certainly it would not be a huge leap in logic to assume that performance will change based on the current mixture. It would not be a case of you getting either 285 hp (regular 87 octane) or 297hp (e85 105 octane). I believe that using increasingly higher octane rated gasolines will show proportionately improved performance.

They don't though...... Premium gas with no alcohol content as many of them are will not show any changes over running E5, or E10 87 octane fuel. It can't discern premium fuel from regular and thus doesn't care what you run. If you get high enough percentage of alcohol in the tank it flips to the E85 tables.....

[Donstar]

They don't though...... Premium gas with no alcohol content as many of them are will not show any changes over running E5, or E10 87 octane fuel. It can't discern premium fuel from regular and thus doesn't care what you run. If you get high enough percentage of alcohol in the tank it flips to the E85 tables.....

Thank you. My understanding of octane is lacking. The significance of the high octane rating of e85 does not seem to be the contributing factor in improved horsepower.

[Badass69]

Donstar, on 04 Jan 2016 - 11:34 AM, said:

Thank you. My understanding of octane is lacking. The significance of the high octane rating of e85 does not seem to be the contributing factor in improved horsepower.

 

Well yes actually it is....... it's the only reason that the engine gets a higher rating than gasoline. If GM tuned your truck for premium fuel from the factory it likely could achieve somewhat similar numbers to E85..... E85 should make more power based on it's resistance to burn but premium fuel is more resistant than regular. But they don't..... they tune it for 87 and what should be safe parameters for 87 octane gas and then what should be safe parameters on E85. It's not an multivariable chart in between... it's set tables based on how whether there is enough alcohol to run on the E85 parameters and if not run on the regular fueling/spark tables. That's all there is to it.

 

If your truck feels better on premium gas which is really of no surprise it's only because it was knocking and retarding timing on 87. You could try midgrade and see what it does..... it may be enough to achieve the same "feeling" as premium. The only vehicle I ever owned that truly liked anything above what was recommended stock was an 97 Monte Carlo I had.... I never datalogged the car but I consistently ran midgrade and achieved about 2 mpg better highway than on 87. Premium fuel in that car did nothing more for it than 89 did.

[Donstar]

Thanks again. I really appreciate you taking the time to add some clarity. GM says to use "'a posted octane rating of 87 or higher". A misconception here is that 87 is a minimum and in turn suggesting (to me) that higher may be better. The comments posted on this forum suggest that only use higher octane if the minimum octane is causing engine knocking. A significant increase in power will only be gained by burning mostly alcohol based gasolines which is no different than the days of carbureted engines!

[Donstar]

I found this YouTube video on octane. It explains very clearly the advantages and, in most cases, disadvantages of switching to higher octane rated fuel. I found it humorous and very informative.

[HondaHawkGT]

Perhaps it is a case of less knock retard during wot with higher octane fuel as the knock sensors will detect less knock on premium gas

 

I can't speak for the 4.3L but the Gen V 5.3 on 87 octane has a noticeable amount of knock. In the summer with the AC on, I had noticed the engine bouncing off the knock sensors without WOT. The power loss was definitely noticeable. Tuners like Justin at Blackbear Performance and the Lingenfelter guys have said there's quite a bit of knock retard on 87 octane and even completely stock trucks should run 89 octane.

 

Seems like most manufacturers in the attempt to make engines with higher specific output (HP/Liter) have been using factory tunes that really push what can be done with 87 octane (aka piss), relying on the knock sensors to pull timing to avoid detonation at the expense of power and to a degree, efficiency.

 

Good example:

http://www.torquenews.com/106/ford-mustang-ecoboost-loses-big-power-87-octane

 

 

Someone in the Mustang6g.com community got ahold of a Ford training manual that explains that when the 2015 Mustang EcoBoost is run on 87 octane, the computer adjusts for that reduced fuel quality. When the computer makes those adjustments, it reportedly reduces horsepower from 310 down to 275 while torque drops from 320lb-ft to 300lb-ft. This is a pretty significant decline for something as seemingly minor as lower octane fuel, but it goes to show how important it is to run premium fuel in a performance vehicle. The extra cost is worth the money, especially in the case of the 2015 Mustang.

 

Those lowered power figures account for an 11% reduction in horsepower and a 6% decline in torque, although it was originally believed that running 87 octane in the 2015 Mustang EcoBoost would reduce power by some 13%. For those who don’t want to do the math, a 13% reduction in power would give the 4-cylinder Mustang around 270 horsepower.

 

 

[HondaHawkGT]

Thanks again. I really appreciate you taking the time to add some clarity. GM says to use "'a posted octane rating of 87 or higher". A misconception here is that 87 is a minimum and in turn suggesting (to me) that higher may be better. The comments posted on this forum suggest that only use higher octane if the minimum octane is causing engine knocking. A significant increase in power will only be gained by burning mostly alcohol based gasolines which is no different than the days of carbureted engines!

 

Most of the performance gain of using E85 is because GM uses the cooling effect of ethanol to its advantage. The injector sprays the ethanol onto the piston and creates a cooling effect, allowing the engine to run more timing and therefore, make more power.

 

And so everyone understands, E85's octane isn't really 105...

 

"If a retailer chooses to post octane, they should be aware that the often cited 105 octane is incorrect. This number was derived by using ethanol’s blending octane value in gasoline. This is not the proper way to calculate the octane of E85. Ethanol’s true octane value should be used to calculate E85’s octane value. This results in an octane range of 94-96 (R+M)/2. These calculations have been confirmed by actual-octane engine tests."

https://en.wikipedia.org/wiki/E85#Octane_rating

 

Also keep in mind E85 isn't 85% ethanol in the winter... it's usually diluted with more gasoline in the wintertime and hovers around 70-75% ethanol.

[Willshire]

 

I can't speak for the 4.3L but the Gen V 5.3 on 87 octane has a noticeable amount of knock. In the summer with the AC on, I had noticed the engine bouncing off the knock sensors without WOT. The power loss was definitely noticeable. Tuners like Justin at Blackbear Performance and the Lingenfelter guys have said there's quite a bit of knock retard on 87 octane and even completely stock trucks should run 89 octane.

 

Seems like most manufacturers in the attempt to make engines with higher specific output (HP/Liter) have been using factory tunes that really push what can be done with 87 octane (aka piss), relying on the knock sensors to pull timing to avoid detonation at the expense of power and to a degree, efficiency.

 

Good example:

http://www.torquenews.com/106/ford-mustang-ecoboost-loses-big-power-87-octane

 

 

 

Anyone with an autocal or like device could load the PID's into it, select KR from the PID menu and drive the truck. And report back how much knock retard they are experiencing in degrees. My BBP tuned 08 had up to 8* of KR at shift points and 4* at WOT on 87 octane, on the 87 octane tune. I consider myself one of the lucky ones as i have gas cards from my work. I am unlucky in the fact that they only allow me to use 87. if you want the truck to last, and you don't beat on it like it's your unruly dog, 87 octane will be fine. if you like to show off to ford and dodge guys, all the time, that your truck has balls maybe go to mid or hi grade gas. If the manufacturer recommended is 87, they have engineered the vehicle to withstand it. if you change the vehicle to make it perform better, you are likely running 89 or better anyways