[Jaybone76]

from the manual:

Recommended Fuel
Use regular unleaded gasoline with
a posted octane rating of 87 or
higher. If the octane rating is less
than 87, an audible knocking noise,
commonly referred to as spark
knock, might be heard when driving.
If this occurs, use a gasoline rated
at 87 octane or higher as soon as
possible. If heavy knocking is heard
when using gasoline rated at
87 octane or higher, the engine
needs service.

So I am wondering if I use a higher octane like 93 will the motor produce more power? This motor has a high compression ratio so it would make sense... I'm talking about the 2.4L with a compression ratio of 11.4:1

 

[Mobius]

Using higher octane gas will not provide more power in this instance. It'll basically just be a waste of money.

The vehicle is tuned to use 87 octane from the factory. The fuel injector timing and pulse-width, and the spark timing have been optimized to provide maximum power and fuel economy with an air-fuel ratio that GM deems safe for the engine. Using higher octane gas would allow for the tune to be adjusted to provide more power and/or better fuel economy, but that would require an aftermarket engine management system and dyno time. The factory EMS won't do it on it's own, at least as far as I know.

On another note, I am surprised that the manual states that engine knock may be heard when using gas rated less than 87 octane. Usually newer vehicles will detect the knock and retard timing (and therefore power) until the proper gas has been put in, to prevent damage to the engine. Does anyone know if GM ECU's do this?

 

[scottyyyc]

Using a higher octane will not give you more power; octane has never been about delivering power. Octane levels started to become important to help reduce engine knock. For some reason, the general public equates Octane with power.

The most important thing is using whatever octane the engine is rated for. Engines are specifically designed and tuned for specific Octane levels. Using premium won't do anything for you. It's more important where you fill up, and the quality of the Gas.

I've used different octane levels of gas on bikes of mine (very high performance inline-4 engines), ranging from 87 to 95, and neither I or a dyno can tell the difference. You basically have to completely re-map your whole ECU to be able to take advantage of it.

 

[GMCdriver]

However, around here the various grades of gas are also tied to the % of ethanol that is blended into the fuel.
All of the Regular 87 octane gas I can find here has 10% Ethanol blended in while the Premium 91 octane gas they offer is usually pure Gasoline (with that 94 octaine/10% Ethanol stuff they sell at Husky/Mohawk stations being the biggest exception.)
I've got a few small engines(Honda Snowblower, 2 stroke String trimmer, etc) that, while they are perfectly happy with 87 octane, they do not like any Ethanol at all and as such I've started buying 91 octane G100 instead of 87 Octane E10 for my gas cans at home.
Also, and this is strickly anticdotal, my 1200cc Bandit(air cooled I4 motorcycle) seems to have trouble with engine cooling when I run 87 octane E10 but displays no such issue on 91 octane G100. I personaly believe this has more to do with the Ethanol then it does with the octane of the fuel as the bike is tuned to run on regular 87 octane pump gas.

 

[monaco]

Using a higher octane will not give you more power; octane has never been about delivering power. Octane levels started to become important to help reduce engine knock. For some reason, the general public equates Octane with power.

The most important thing is using whatever octane the engine is rated for. Engines are specifically designed and tuned for specific Octane levels. Using premium won't do anything for you. It's more important where you fill up, and the quality of the Gas.

I've used different octane levels of gas on bikes of mine (very high performance inline-4 engines), ranging from 87 to 95, and neither I or a dyno can tell the difference. You basically have to completely re-map your whole ECU to be able to take advantage of it.




There are a few cars on the market that have 2 horse power ratings depending on fuel used. The Hyundai Genesis(with the v8) is one of these cars. The two ratings are published in both the manual and in brochures. I have a Chev SSR with the corvette 6.0 liter engine and the manual recommends 91 octane. If a lesser octane is used than performance will decrease, again this is according to the manual. That being said I can not tell any difference with my driving regardless of fuel used. The next thing that bothers me is even though I am paying extra for hi octane fuel is that what I'm getting?

 

[Mobius]

There are a few cars on the market that have 2 horse power ratings depending on fuel used. The Hyundai Genesis(with the v8) is one of these cars. The two ratings are published in both the manual and in brochures. I have a Chev SSR with the corvette 6.0 liter engine and the manual recommends 91 octane. If a lesser octane is used than performance will decrease, again this is according to the manual. That being said I can not tell any difference with my driving regardless of fuel used. The next thing that bothers me is even though I am paying extra for hi octane fuel is that what I'm getting?

I'd have to say, with the amount of torque and power put out by the stock 6.0L, losing a few ponies will be hard to feel with a 'butt dyno'. Fuel economy would be an easier way to tell, because the vehicle may not be as efficient with 87 vs 91 (given that knock is detected and the timing is retarded). It's a safety buffer for the motor. You could run quality 87 octane fuel through your motor for it's entire life and never encounter any knock, while having the same performance as if you were using 91. However, a motor is a dynamic beast, and I'd rather have that buffer than risk detonation.

The Genesis is tuned from the factory to a fairly ragged edge to get the best performance and fuel economy, far closer to that edge than most manufacturers. Hence the two HP numbers. Running 87 in that car will require the ECU to use a different timing map (reducing power) to avoid damage to the engine.

Ha, if you can't tell, I'm paranoid about knock. Most piston engines can withstand quite a bit of detonation before any serious damage is done. However, for rotary engines (which is what I am most familiar with), even minor detonation can be instant death for the engine.

 

[scottyyyc]

There are a few cars on the market that have 2 horse power ratings depending on fuel used. The Hyundai Genesis(with the v8) is one of these cars. The two ratings are published in both the manual and in brochures. I have a Chev SSR with the corvette 6.0 liter engine and the manual recommends 91 octane. If a lesser octane is used than performance will decrease, again this is according to the manual. That being said I can not tell any difference with my driving regardless of fuel used. The next thing that bothers me is even though I am paying extra for hi octane fuel is that what I'm getting?

In higher performance engines, octane can make a small difference. From what I've read, it's usually very minute anyways. Ina regular consumer vehicle and engine, we're talking 1 or 2 ponies here.

Various companies also put higher levels of detergents or additives to higher octane fuels as well, but more as a marketing effort and to help the fuel sell. Octane, in and of itself, is of no real concern to the consumer. Just use what the engine is rated for.

 

[stylegal]

Re: Octane rating question and Top Tier gas

So what are your opinions regarding GMC recommendation, on the very same page of the owners manual, to use gas rated as Top Tier?

This is my first GMC (Explorer convert) so I have never heard of Top Tier and only stumbled on this perusing the 400+ page owners manual.
Would greatly appreciate comments.

From Manual:
"Use of the recommended fuel is an important part of the proper maintenance of this vehicle. To help keep the engine clean and maintain optimum vehicle performance, we recommend the use of gasoline advertised as TOP TIER Detergent Gasoline.
Look for the Top Tier label on the fuel pump to ensure gasoline meets enhanced detergency standards developed by auto companies. A list of marketers providing TOP TIER ddetergent Gasoline can be found at www.toptiergas.com "

Regards,
Stylegal

 

[GMCdriver]

To be a Top Tier Gas station, a company must meet the "top tier standards" with all the grades of gas that they sell.
Top Tier gas refers to standards for detergent levels above those required by the EPA.
The companies that require/reccomend Top Tier gas are General Motors, Honda, Toyota, BMW, Audi and Volkswagen.
The stations that carry Top Tier Gas are:
QuikTrip
Chevron
Texaco
MFA Oil Co.
Conoco
Phillips 66
76
Entec Stations
Shell
The Somerset Refinery, Inc.
Kwik Trip / Kwik Star
Aloha Petroleum
Tri-Par Oil Co.
Turkey Hill Minit Markets
Mileage Stations
Road Ranger
CountryMark
Chevron Canada
Shell Canada
Petro-Canada
Sunoco Canada

If a vehicle calls for 87 octane Top Tier then the regular gas from any of those stations should be fine.

 

[scottyyyc]

Top Tier gasolines refer to a detergent standard set by the automakers (virtually all of them). It refers to the level of detergents in the gasoline. Direct injected engines like in the Terrain/Nox (and modern engines in general) need cleaner gasolines with higher levels of detergents to operate properly in the long run. With DI, if you continually use dirtier gasolines, you can get a bit of carbon build-up on valves and spark plugs. Top-Tier doesn't have anything to do with Octane.

Basically, use good quality clean gas whenever possible. Shell is typically known to be excellent, as are others.

For more info - http://www.toptiergas.com/

 

[stylegal]

So what I hear you saying is, yes follow the recommendation to use Top Tier gas as it will keep the engine happier in the long run.
And a happy engine is a good thing!!!
Thanks.
Stylegal.

 

[Jaybone76]

I have ssen on the internet about DI engines can have a problem with sludge buildup in the intake valves you can google it to check it out.. so I guess thats why they want us to use the top tier **** to cut down oin this problem.

 

[GARYD]

I use 87 octane in all my vehicles. Harley, Aztek and in my Corvettes. The only time I use premium is when I want the full potential use of the vehicle....like racing or driving in the mountains.
I read someplace once if your manual says "recommend premium" you can use any grade, but if the manual says "reqiures premium" then you have to use it.
Once or twice I throw in a can of injector cleaner since I use the cheapest gas I ca find....usually Speedway.
I don't know much about the DI engines, maybe I should switch over to Shell or Mobil - they were my favorites when I was a youngster back in the 50's/60's

 

[Steve A]

The big problem with the Ethanol enhanced gasolines is the amount of mileage per gallon/litre that you lose.

If any of you raced any fuel engines - alcohol in this case - you'll remember that the A/F ratio on "Alky" is around 6 to 1, roughly double what the best A/F for gasoline is. So, it takes twice as much fuel to go the same distance. Also, it will lean out the A/F mixture roughly the same percentage as the amount added to the gasoline. This really doesn't make all that much difference as most ECU controlled engines are set up to run fairly rich for safety purposes. That is, safety for the mfr's on warranty repairs.

That is why a # of people run and say they get better mileage with Ethyl/Premium because most of it doesn't have any Ethanol added to it. Higher octane just means the fuel burns slower which reduces "knock" and will usually allow more spark advance.

 

[GMCdriver]

The big problem with the Ethanol enhanced gasolines is the amount of mileage per gallon/litre that you lose.

If any of you raced any fuel engines - alcohol in this case - you'll remember that the A/F ratio on "Alky" is around 6 to 1, roughly double what the best A/F for gasoline is. So, it takes twice as much fuel to go the same distance. Also, it will lean out the A/F mixture roughly the same percentage as the amount added to the gasoline. This really doesn't make all that much difference as most ECU controlled engines are set up to run fairly rich for safety purposes. That is, safety for the mfr's on warranty repairs.

That is why a # of people run and say they get better mileage with Ethyl/Premium because most of it doesn't have any Ethanol added to it. Higher octane just means the fuel burns slower which reduces "knock" and will usually allow more spark advance.

While you will loose mpg due to the lower BTU rating of Ethanol vs. Gasoline, some of the new ECUs are being programmed to alter their engine tuning when E85 is detected to offer higher power output.

Take GM's FlexFuel 5.3 for example:
http://archives.media.gm.com/us/powertrain/en/product_services/2010/gmna/HPT%20Library/Gen%20IV/Gen%20IV%20Truck/2010_Vortec_53L_LMG_Sierra_Combo.pdf

 

[Steve A]

Nice graph, but, if you don't take the readings at the same RPM the results will be rather erroneous and misleading.

 

[GMCdriver]

Nice graph, but, if you don't take the readings at the same RPM the results will be rather erroneous and misleading.

Incorrect.
A much better understanding of an engine's power characteristic can be assertained by looking at it's torque output through out it's entire RPM range.

 

[gearhead]

The big problem with the Ethanol enhanced gasolines is the amount of mileage per gallon/litre that you lose.

If any of you raced any fuel engines - alcohol in this case - you'll remember that the A/F ratio on "Alky" is around 6 to 1, roughly double what the best A/F for gasoline is. So, it takes twice as much fuel to go the same distance. Also, it will lean out the A/F mixture roughly the same percentage as the amount added to the gasoline. This really doesn't make all that much difference as most ECU controlled engines are set up to run fairly rich for safety purposes. That is, safety for the mfr's on warranty repairs.

That is why a # of people run and say they get better mileage with Ethyl/Premium because most of it doesn't have any Ethanol added to it. Higher octane just means the fuel burns slower which reduces "knock" and will usually allow more spark advance.

That there is some great information, thanks Steve A.
We usually put in higher octane when the price per litre/gallon dips, which it usually does mid week, if we have to fill up.
Maybe we'll do it more often for the Terrain.
The two other cars, well, they've survived this long on mostly 87 octane LOL!

 

[gearhead]

Incorrect.
A much better understanding of an engine's power characteristic can be assertained by looking at it's torque output through out it's entire RPM range.

I haven't seen a 2.4 or 3.0L DI torque curve yet, but seat of the pants tells me it isn't very flat across the RPM band, that's for sure LOL!
From my real "gearhead" days of yore, not too many factory engines could boast a nice flat torque curve between 1500 or 2 grand and redline.
Our V6 AWD Auto Terrain is definitely not tuned for max torque at low RPM.
Just saying we have to look at real world numbers here, not those in a dyno lab...

 

[GMCdriver]

I haven't seen a 2.4 or 3.0L DI torque curve yet, but seat of the pants tells me it isn't very flat across the RPM band, that's for sure LOL!
From my real "gearhead" days of yore, not too many factory engines could boast a nice flat torque curve between 1500 or 2 grand and redline.
Our V6 AWD Auto Terrain is definitely not tuned for max torque at low RPM.
Just saying we have to look at real world numbers here, not those in a dyno lab...

I4
http://archives.media.gm.com/us/powertrain/en/product_services/2010/gmna/HPT%20Library/Ecotec/2010%20Ecotec%2024L%20LAF%20Terrain%20SAE.pdf

V6
http://archives.media.gm.com/us/powertrain/en/product_services/2010/gmna/HPT%20Library/HFV6/2010%2030L%20LF1%20Terrain.pdf

I can find pretty much any GM you would want to see going back to about 2005.

I understand that there are various parasitic losses throughout the entire drive line that reduce the power output at the wheels from what would be measured at the crank in a dyno lab but comparing full torque & hp curves based on measurments taken at the crank in a dyno lab still tells us way more then simply comparing the peak number achieved at any single speciffic engine speed.