4.3 litre V6 Ecotec3 and gasoline octane

[Donstar]

Using premium fuel in a vehicle designed for regular fuel is often referred to as a waste of money and no benefit to performance. I believe the Ecotec with flex fuel engine's performance improves with higher octane gasoline. General motors posts different horsepower ratings for a vehicle using regular fuel (87 Octane) and one using E85 (100 Octane). It is logical that octane ratings of 89, 91,and 94 would come in between these two. Currently I am using Shell 89 octane gasoline and see consistently favourable MPG over the Shell 87 Octane I was previously using. My manual says to use 87 or higher. Please let me know if my logic is correct or how it is flawed.

[fondupot]

Using premium fuel in a vehicle designed for regular fuel is often referred to as a waste of money and no benefit to performance. I believe the Ecotec with flex fuel engine's performance improves with higher octane gasoline. General motors posts different horsepower ratings for a vehicle using regular fuel (87 Octane) and one using E85 (100 Octane). It is logical that octane ratings of 89, 91,and 94 would come in between these two. Currently I am using Shell 89 octane gasoline and see consistently favourable MPG over the Shell 87 Octane I was previously using. My manual says to use 87 or higher. Please let me know if my logic is correct or how it is flawed.

 

You are correct for running 89 octane. With Direct Injection and high compression ratios, these motors will run better on 89 over 87.

[Donstar]

 

You are correct for running 89 octane. With Direct Injection and high compression ratios, these motors will run better on 89 over 87.

Thanks for responding. I believe this to be a real attribute to these engines and it surprizes me that this isn't advertised. Owners can be pleased with the performance using regular gas knowing that it will get even better with higher octane! I do a lot of city driving and seldom saw anything better than 17L per 100km using regular gas. I am on my second tank of mid grade and have yet to get as high as 17 again. I am usually 15L or 14L. per 100 km.

[Donstar]

 

You are correct for running 89 octane. With Direct Injection and high compression ratios, these motors will run better on 89 over 87.

It appears that I started two threads on an almost identical topic. The other thread titled, 2015 Sierra 4.3 L and high octane fuel has many informative comments and has been fairly active. It is very interesting to me that after receiving all of this feedback and all of my subsequent research, your advice was right on the mark, right from the beginning! I now have a far better understanding of why 89 is the best option, but I wanted to thank you, Fondupot, once again!

[Northwoods]

Why is 89 the best option? Will it give the same output as e85?

[Geiser100]

I ran a full tank of 93 octane fuel in my 4.3 but didn't notice any change. It has been bitter cold lately and my mileage has actually decreased from 16.3 to 15.8. So when it warms up I will put high octane fuel in again.

[GDI Tech]

With an old port injection engine that was 9.0-9.5:1 CR using anything other than 87 was a waste as the low compression ratio would give no benefit. BUT, with GDI engines (these are 11.0-11.5:1 CR) using 87 is fine as the knock sensors will pull timing if detonation is detected, but if you run 91 or 93, you will make more power and get slightly better fuel economy due to less incidence of detonation allowing the engine to operate at optimum timing advance. So, the old accurate adage of anything above 87 is a waste no longer applies. The owners manual indicating 87 is a marketing bullet as these can run fine with no damage resulting, but due to the higher CR there is power and economy left on the table so the marketing can focus on less expensive fuel, and also less expensive oil (the cheap DEXOS syn blend VS full synthetic) even though full synthetic is far better for longevity and less valve coking, etc. One most look at the target market, or demographic the automaker is focused on appealing to. GDI allows the use of any octane to 93 (or higher) since fuel is no longer present during the compression stroke to cause detonation for the most part. Now, the added MPG is about a wash when you pay more for the 93, but the power is what I like. So, no harm running 87, but your engine will like 91-93 much better as it can fully use that higher compression ration and maintain optimal ignition advance (there are two tables in the timing cells of the tune, 87 usually will keep it defaulted to the low octane table. You may need to do a battery disconnect to allow the ECU to default to the high octane tables if you want to see a quick difference when filling with 93 if you had been running 87 as it can take 50-100 miles of driving before the ECU will use the high octane tables automatically. All depends on the knock incidence it has been seeing.

 

So much has to be relearned when it comes to GDI fuel injection on these new engines.

 

Also something the owners manual does NOT advise, is GET THAT factory fill oil out at 500 or so miles....do NOT go 5-10k miles on the first fill as that oil is full of debris and metal from break-in!

[crafferty]

Why is 89 the best option? Will it give the same output as e85?

e85 is 110octane, you are not going to see nearly the same results running that instead of 89.

[Northwoods]

If using 89 or higher gas (not e85) will it still get about the same mileage as 87 with an increase in power? Or will the mileage decrease like e85

[GDI Tech]

You will get better MPG due to the reduction of timing pulled for knock retard.

 

E85 is majority ethanol, and the ratio of Ethanol/Methanol as a fuel compared to gasoline, it takes nearly 3 times the alcohol to create the same stoiometric A/F ratio needed, so you will always get worse fuel economy with any alcohol content. E85 is an excellent fuel for making power with big boost/higher CR, but not a good fuel for longevity of any metal components it comes into contact with. Today's fuel systems are all coated to combat this, but those that have used it long tern see it still manages to "wick" plenty of moisture into the fuel, especially in humid climates like FL, etc.

 

So, your best power and economy will come from 93 w/NO ethanol. As the ethanol content rises, MPG will go down.

[Northwoods]

I have seen "octane booster" additives available. Would something like this improve power in our trucks?

[GDI Tech]

Octane boosters vary in the amount of points they can raise octane, and with what chemicals they use to do so. When you look at the contents, it is best IMHP to just use 91 or 93 octane from the pump. The added MPG will not save you $ as the added cost of the premium fuel cancels out any added MPG, but the added power is worth it.

 

Here is the straight scoop. Octane boosters usually contain one active ingredient, sometimes diluted in a solvent (like toluene). Typical active ingredients for octane improvers are alcohols, ethers, manganese (MMT), or tetraethyl lead (TEL).

Alcohols:

Methanol and ethanol are alcohols which have been used as octane boosters. They work since both have a higher octane number than typical street gasolines. They are more effective in low octane gasolines than in high-octane gasolines. Alcohols have an affinity for water. This means that if there is a slight amount of water in the bottom of your gas tank, the alcohol can grab hold of the water and separate from the gasoline, leaving you with a water/alcohol mix at the bottom of your tank with gasoline floating on top. This is not good. And the last thing, even if you mix octane improvers containing alcohols with your gasoline, you will still not know what octane you end up with.

Ethers:

MTBE, TAME and ETBE are the most common ethers available for gasoline use. They have higher octane values than typical gasoline, so like the alcohols they will increase the octane quality of street gasolines. Ethers do not have an affinity for water, will not separate from gasoline, and blend like a hydrocarbon. When ethers are used as additives, the enthusiast still does not know what his final octane number is.

Manganese (MMT):

Sometimes referred to as manganese, or more correctly Methyl Cyclopentadienyl Manganese Tricarbonyl (MMT). This can be an effective octane improver at very low concentrations. You can gain one or two octane numbers using the recommended treat rate. Problems with emissions, injectors, spark plugs, oxygen sensors, and catalytic converters have all been traced to the use of MMT, which is why it is not legal to use by US Refiners in Reformulated Gasoline. As indicated above with the alcohols and the ethers, it is tough to know what octane number you have attained.