Fuel octane revisted...

[DragonSky]

Okay, I've searched this forum and read all of the comments about whether to run regular or premium in my base Sky, and the manual says to run premium. So, I was sure that was the thing to do until I picked up my car last Thursday. Just before I drove away my salesman told me to run regular in it! I replied that the owners manual said to run premium, and he said that was only for the turbo, but I don't see that in the manual. He said the dealership filled it with regular, so that's what it was running anyway. When I had to fill it, I used premium, but I really didn't notice any difference in performance, and I didn't hear any pinging with the tank of regular. Am I wrong to rethink my original decision? The difference in cost is not huge, and I like to take excellent care of my vehicles, but I do like to save money when I can. Now I'm really confused...

[fr0stb1t3]

On the base sky I'd say just go for regular. Premium is necessary for all the boost the turbo throws out to keep it from knocking. Technically in the redline you can run regular as well, but the ECU is going to cut back on the boost/timing to counter the increased chance of knock.

[Bogie]

Both models are designed to "handle" regular. They "handle' regular by managing the engine if a knock condition is detected.

The kappa engineers have stated you need Premium in the turbo in order to get full power performance.

I don't know if you lose top end power on the NA. It does have a pretty high compression ratio.

[fr0stb1t3]

Originally Posted by Bogie

Both models are designed to "handle" regular. They "handle' regular by managing the engine if a knock condition is detected.

The kappa engineers have stated you need Premium in the turbo in order to get full power performance.

I don't know if you lose top end power on the NA. It does have a pretty high compression ratio.

What's the C/R?

Edit: Found it, 10.4:1; with that bit of knowledge I revise my previous statement and I would personally run premium in it. It's only a few dollars a fill up and you probably get a few more horses up top. If it's a big deal to you regular shouldn't cause any harm and the ECU should compensate.

[Bogie]

Originally Posted by fr0stb1t3

What's the C/R?

9.2 on the Turbo.
10.4 on the NA.

[fr0stb1t3]

Originally Posted by Bogie

9.2 on the Turbo.
10.4 on the NA.

My sales guy tried to tell me I should run regular in the Redline. I laughed.

[DragonSky]

Originally Posted by fr0stb1t3

My sales guy tried to tell me I should run regular in the Redline. I laughed.

I can relate, as much as I'd like to think that salesman know everything about the cars they are selling, I know that's often not the case. I think I'll just keep running premium, it's not that big of a deal financially.

[08SkyLdr]

My dealer told me before leaving that I should run Premium and no ethanol. I have tried I tank of Regular Plus (88-89 octane) and could tell a difference in performance and ping noise. I have since been running nothing but premium.

The biggest problem I see now is trying to find the stations that aren't putting in the ethanol in all their products. I don't have the pinging noise with the premium and ethanol, but I have seen a decrease in MPG's because of it.

Outside of checking each station or calling around, has anyone found or even looked at how to determine who has pure gas vs. the gas with ethanol?

[JRinKY]

I have run regular, plus, and premium in my NA, and cannot tell any difference in driveability. I have not detected any knock or ping. I have recorded effectively identical fuel mileage with each grade. Using my G-Tech I have measured apparent engine power and gotten virtually the same reading with each grade of fuel.

As near as I can tell, for the conditions in my area, and using Chevron fuel, there is no advantage to using premium.

[Gerry]

Whether there is an advantage or difference in how the engine performs depends upon how you use the car. If you're light on the throttle and the engine doesn't normally see high loading, then there won't be much difference. If you take advantage of the engine's power, then there will be a difference. It comes down to how the knock sensor is managing the ignition timing curve. The blatant evidence would be born out of the datastream for the ignition advance. Lower ignition advance means less power and lower fuel economy. Higher advance gives you the opposite. It's a tough call and you can't apply a universal answer to every situation. And it's hard to make the call with just one blended (some regular and some premium) tank of gas. I'd say try each for a month. This will give you higher resolution in your measurements and you can make a decision based upon the more abundant information.

[JRinKY]

Gerry : Whether there is an advantage or difference in how the engine performs depends upon how you use the car. If you're light on the throttle and the engine doesn't normally see high loading, then there won't be much difference. If you take advantage of the engine's power, then there will be a difference. It comes down to how the knock sensor is managing the ignition timing curve. The blatant evidence would be born out of the datastream for the ignition advance. Lower ignition advance means less power and lower fuel economy. Higher advance gives you the opposite. It's a tough call and you can't apply a universal answer to every situation.

The G-Tech calculates power by measuring acceleration during a WOT acceleration run, so spark advance is certainly accounted for. I have a long straight section of road that is mostly flat and that seems to run perpendicular to the prevailing wind. Runs over the time that I have been testing with the G-Tech have resulted in power measurements within a 10 hp range. I have tried to maintain conditions as constant as possible, but temperature, humidity, barometric pressure and wind are all variables that will change developed power so the readings vary from day to day. My tests have shown no statistically significant change with fuel grade. There may be one, but it isn't very big.

And it's hard to make the call with just one blended (some regular and some premium) tank of gas. I'd say try each for a month. This will give you higher resolution in your measurements and you can make a decision based upon the more abundant information.

I ran each grade of fuel for a minimum of 5 tankfuls, and driving essentially the same cycle revealed no change in overall fuel economy. The exception to this was the first tank of premium after a steady diet of regular, when mileage jumped by about 4 MPG. The second tank saw a return to my normal 24 MPG. My daily drive cycle is 6 miles of stop-and-go, 4 miles of normally high-speed country road, 5 miles of highway, and a mile of stop-and-go, then a reversed return home.