2015 Sierra 4.3 L and high octane fuel

Donstar · November 28, 2015

I have read several threads on the 4.3 six cylinder engine. I really enjoy some of the debates. I have owned many pickups equipped with a variety of power configurations over my past 45 years of driving. I believe this particular motor to be a wonderful balance between power and economy. (I also believe it would lend itself well to being offered with a truck type manual transmission) My question is if this motor would get a boost in power if you used high octane gasoline. I have read that the E85 fuel gives more power but is not available where I live. I am not suggesting this motor is underpowered, but like most, I like to play with my truck! There are many knowledgeable people on this forum and will know if upgrading my fuel will translate to more power or wasted money!

1500fp · December 30, 2015

If i recall there is a page in the owners manual that goes over this. E85 actually has less "power" when you compare a gallon of E85 to regular gas (stored potential energy). So burning a gallon of E85 will produce less energy than burning a gallon of regular gas.

Sooperdave · December 30, 2015

I have read several threads on the 4.3 six cylinder engine. I really enjoy some of the debates. I have owned many pickups equipped with a variety of power configurations over my past 45 years of driving. I believe this particular motor to be a wonderful balance between power and economy. (I also believe it would lend itself well to being offered with a truck type manual transmission) My question is if this motor would get a boost in power if you used high octane gasoline. I have read that the E85 fuel gives more power but is not available where I live. I am not suggesting this motor is underpowered, but like most, I like to play with my truck! There are many knowledgeable people on this forum and will know if upgrading my fuel will translate to more power or wasted money!

Wasted money. Upping the octane will not produce more power in engines that don't require it. The higher octane of the E85 does so by way of it's programming when it recognizes this type of fuel. You can achieve more power by some simple bolt-ons such as an air intake, exhaust, and computer tuning.

Txjose · December 30, 2015

Honestly if you are not tunned for the higher octane fuel you will not see a big difference.

Donstar · December 30, 2015

If i recall there is a page in the owners manual that goes over this. E85 actually has less "power" when you compare a gallon of E85 to regular gas (stored potential energy). So burning a gallon of E85 will produce less energy than burning a gallon of regular gas.

Thanks for your comment. When I read statements such as this found in "Car and Driver" it makes me curious. GM’s latest FlexFuel truck engines get an output bump from ethanol, which helps the new V-6 make 297 horses and 330 pound-feet of torque. Ethanol’s downside is that, owing to a lower energy density than gasoline, it hurts fuel economy; the EPA combined estimate for a V-6, four-wheel-drive Silverado drops from 19 miles per gallon to just 13. This indicates to me a considerable "power" difference from 285hp and 305 torque with regular octane gas. How can the vehicle respond to these two different fuel types without some effect from the "in-between" grades?

CAtaylor · December 30, 2015

Thanks for your comment. When I read statements such as this found in "Car and Driver" it makes me curious. GM’s latest FlexFuel truck engines get an output bump from ethanol, which helps the new V-6 make 297 horses and 330 pound-feet of torque. Ethanol’s downside is that, owing to a lower energy density than gasoline, it hurts fuel economy; the EPA combined estimate for a V-6, four-wheel-drive Silverado drops from 19 miles per gallon to just 13. This indicates to me a considerable "power" difference from 285hp and 305 torque with regular octane gas. How can the vehicle respond to these two different fuel types without some effect from the "in-between" grades?

Because the truck has sensors to measure alcohol content. The only thing to measure octane is the knock sensors. If there is no knock detected on 87 it is not pulling any timing. If it isn't pulling timing there is nothing to gain by increasing octane.

robvas · December 30, 2015

E85 actually has less "power" when you compare a gallon of E85 to regular gas (stored potential energy). So burning a gallon of E85 will produce less energy than burning a gallon of regular gas.

True - that's why the gas mileage on E85 is much worse - because the truck uses more fuel to make the same amount of power. And it can even use a little bit more to make additional horsepower on E85 (from advancing the timing) than it can on regular gasoline.

Donstar · December 30, 2015

I find this interesting. I probably do not understand "octane". If sensors can accommodate changes in alcohol content then I would think they would respond when a premium fuel is added. I am thinking that a higher grade of gasoline would burn more efficiently. This would result in either less fuel required or more power generated. I am ok with being wrong, it just doesn't make sense to me that higher octane gas doesn't impact performance.

Willshire · December 31, 2015

High octane gas resists detonation better so you can run more timing. Perhaps it's not the octane the sensors detect but the corn alcohol as alcohol will have different o2 characteristics than gasoline. Just a thought

Brian S. · January 2, 2016

Surprised by all the misinformation in this thread.

GM themselves advertises the hp/torque jumps from 285/305 to 297/330 on E85. You won't pick up 12hp, 25lbs torque with an air filter.

I had a 2014 4.3l with the 3.42 gears, and can tell you it felt like a different truck on the E85.

E85 has lower energy content per gallon, but is 105 octane. The Gen V engines use this to bump compression, change timing to achieve the higher power.

5.3l Gen V flex fuel trucks get a big boost from E85 as well.

Donstar · January 2, 2016

Surprised by all the misinformation in this thread.

GM themselves advertises the hp/torque jumps from 285/305 to 297/330 on E85. You won't pick up 12hp, 25lbs torque with an air filter.

I had a 2014 4.3l with the 3.42 gears, and can tell you it felt like a different truck on the E85.

E85 has lower energy content per gallon, but is 105 octane. The Gen V engines use this to bump compression, change timing to achieve the higher power.

5.3l Gen V flex fuel trucks get a big boost from E85 as well.

I'll try asking my question in another way. If the 105 octane in E85 bumps up the 87 octane regular gas performance by 12 hp then will premium 91 or 93 octane show proportionate gains? In other words, if an 18 point increase in octane rating (87-105) gives 12 extra hp will a 6 point (87-93) increase give 4 extra hp?

Willshire · January 2, 2016

from all I have read and all of my experience, hp and torque gains through gas octane ratings, is done by increased timing and/or increased compression. I believe the timing is adjusted on e85 as I do not know if vvt can actually increase compression by changing valve closing events to increase dynamic compression.

Txjose · January 2, 2016

I'll try asking my question in another way. If the 105 octane in E85 bumps up the 87 octane regular gas performance by 12 hp then will premium 91 or 93 octane show proportionate gains? In other words, if an 18 point increase in octane rating (87-105) gives 12 extra hp will a 6 point (87-93) increase give 4 extra hp?

Even if it does, that is within the margin of error. More octane does not mean more horse power instantly. You have to run the fuel for multiple tanks befroe the truck will slightly adjust to the fuel. Regular is what is recommended, unless you are tuned for 91/93 octane then run regular.

Willshire · January 2, 2016

I think I found the answer and it has to do with the stoitchometric air ratio of e85, which is 9.8:1 compared to 14.7:1 of gasoline. Then, through the pcm, it adjusts timing to bring the ratio closer to 14.7:1 thru advanced timing. I may be way off but if I'm close its pure luck lol

Donstar · January 2, 2016

Even if it does, that is within the margin of error. More octane does not mean more horse power instantly. You have to run the fuel for multiple tanks befroe the truck will slightly adjust to the fuel. Regular is what is recommended, unless you are tuned for 91/93 octane then run regular.

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.