Now that the C7 has been out in the real world for over a year.......
What's the verdict about running premium versus regular fuel?
Does the engine really perform better?
Will it hurt the car if you don't run premium gas?

 

I run what the Owner's Manual says to run. Why wouldn't you?

Higher octane fuel isn't about "better performance," it's about protection from knock that can damage an engine.

 

wow...lotsa threads this morning asking us to violate the owner's manual...

Use hi test and go have fun....

 

 

Why would you even bother running regular versus what GM tells you in the owners manual. To save a couple of bucks?

 

My thoughts exactly.

OP - pump premium as the owner's manual reads. As stated above, it is far more than just "better engine performance" with the use of premium.

 

Lots of threads on this subject.

Verdict : Run the recommended grade of gas (91-93)

Yes, engine will perform better. It won't knock under hard acceleration and the computer won't have to adjust timing to allow for the lower octane.

It probably won't if you drive the car normally - meaning no hard acceleration at all. Just putt along and 87 will likely not cause any harm. Is it worth the risk on a $60K-$70K car? Warranty issues if something happens in the engine even if unrelated?

However for a max difference of $6 per tank full of 93 vs. 87, not sure it's worth the savings to not be able to drive the car with a clear conscience, be able to put your foot into if you choose and have some fun.

 

Gasoline is composed of hydrogen and carbon atoms. Octane is gasoline composed of 8 carbon atoms per molecule. The octane rating, traditionally, was a measure of what percentage of gasoline is composed of octane molecules. 90 octane gas is composed of 90% octane gasoline molecules and 10% heptane gasoline molecules and other additives. There are several ways to measure octane which is why you can have gas with an octane rating of over 100.

Octane rating, is anything more misunderstood?

Octane, amongst the gasoline molecules (heptane, octane, nenane, decane) has the desirable characteristic that it can be compressed quite a lot before it spontaneously combusts. It also burns slower. A 4 cycle gasoline car engine doesn’t count on spontaneous combustion. Instead it assumes that combustion will occur when the spark plug fires. If the gasoline combusts before the spark plug fires (beginning of power stroke), the engine will not make maximum power and can be damaged.

The compression ratio of the engine determines the amount of octane you need in gasoline. The higher the compression ratio, the higher the octane percentage. If you use low octane gas, can you live with the effects of pre-detonation?

 

+100. I simply don’t understand someone buying a powerful and fairly expensive sports car and wondering how he/she can ignore the owner’s manual all in an effort to save a few cents per gallon. Maybe he should have gotten a base model Focus. Don

 

Just use what the owner's manual suggests - for everything.

Edit: except oil (unless you have the addendum) :-)

 

If I were in an isolated location where premium wasn't available and I had to have fuel then I would put in standard grade to get me to where the proper stuff is available. And I would drive conservatively and that includes shifting to a lower gear when necessary (either manual or auto transmission) to avoid any situation close to lugging.

But unless you are an independent testing lab trying to test the capabilities of the knock sensors and timing tables or the robustness of the piston faces when subjected to pre-ignition then putting regular grade in a C7 just for the hell of it comes under the heading labeled GOOFY...

 

Typical fill for an "empty" C7 is around 13 gallons. The difference in pricing between "regular" and "supreme" is typically what, 20 cents a gallon? That's $2.60 difference.

Some people's kids.....

 

Gotta pay for that 64oz Big Gulp of Coke somehow!!!

On a serious note, just buy the premium grade and enjoy everything the engine has to offer. Will you hurt anything with 87? Probably not...but the ECU will retard timing and reduce engine output.

 

It probably doesn’t matter all that much to most people, but your octane explanation is grossly incorrect. To measure antiknock properties, octane numbers of zero and 100 were arbitrarily assigned to two specific compounds: n-heptane at zero and 2,2,4 trimethyl pentane at 100. Since 2,2,4 TMP has 8 carbons, it is one of many octane isomers, and the test became known as the octane test. But octane numbers of the various octane isomers range all over the map, with some being near zero. That is true of all carbon numbers, namely, that octane numbers of the various compounds having that many carbons varies widely. In general, if you have a lot of chain branching or an aromatic ring, octane number will be high. Olefinic bonds also help.

What it means if you are 90 octane is that the fuel has the same antiknock performance as a blend of 90% 2,2,4 TMP (the compound rated 100) and 10% n-heptane (the compound rated zero). Gasoline as it comes out of the ground from Mother Nature has an octane of about 60. The refinery must change its chemical composition to introduce more chain branching, aromatic rings, and olefinic bonds, to get it up to the desired level. Premium is more expensive than regular because it must be blended from more severely processed components. Having said that, the marketers charge much more for premium than it really costs to make. The true cost differential to make 93 premium versus 87 regular is about 8 cents per gallon. So what a marketer does is raise the price of premium until its price scares people away. This benefits him on both sides, making more money on the premium, and also allowing him to sell the regular for less by subsidizing it with the profits from premium.

 

40 to 60 cents difference per gallon around here. But, please use the Premium or sell the car.

 

Does everyone use top tier premium gas or any premium gas regardless?

 

Use top tier, that what they ask for....
Get it from a busy station.

 

Older generation FWIW

When I had a daughter living at home and driving the C5 and GTO I would use 87 octane.

It slowed the cars down with no side effects--no knocks--pings--or other adverse effects--and the C5 has been in the house for 17 years.

 

Wrong. Despite a compression ratio of 11.3:1, the Camaro's 3.6L Direct Injection engine is designed to run on regular unleaded fuel.

 

Great explanation; thanks. I have wondered about the regular/premium price difference. Now I know.