Has anyone experimented by using premium gas (or at least half and half) to determine if it does improve MPG?

Informal experiments I've done on other -conventional ICE- vehicles indicate that there is some MPG advantage of doing so. Although most owner manuals state that there is actually no difference in doing so.

Now, I know what you are thinking: "Fernando, the price of gas is already waaaaay too high, why would you want to add more cost?"

The answer is precisely, because of the high cost of gas, it makes sense for the increased MPG. Let me explain.

The price difference between regular and premium is fixed at about $0.20 or so. As a matter of fact, sometimes I've seen a difference as low as $0.16; this regardless of the actual gasoline cost.

So, when regular was $1.00/gal, it was a 20% difference. Nowadays with regular at $2.40/gal, it is only 8%

So, if I get a 15% increase in MPG by switching to premium, I still get an advantage on MP$, where it counts.

Am I making sense, or has the excess oxygen I'm breathing gone over my head?

 

you make sense.

As long as you get >8% increase in mpg you'll come out ahead. If you can get 8%.

Tangentially, I used to have a car that recommended >91 octane. If I used regular (86-87 here) I definitely LOST 10% mpg. But I've never gained by using premium in an engine designed for regular.

 

I did that same experiment a few months ago - results were inconclusive. I had a 52.4 tank on the Super 92 Octane, which had been preceeded by a 47.7 tank on 87 Octane and then followed by a 50.6 tank on 87 Octane. So it was hard to tell if the Octane made any diff at all....

Feel free to try it yourself - each case is different, with different cars, different environments, and even different fuel.

 

So taking your best case 92 and worst case 87 scenarios from your examples above, 47.7 to 52.4 is a 10% increase. Good!

However, there's only a 3.6% increase from the 50.6 tank to the 52.4 tank. Averaging the two 87 tanks (assuming the same amount of gas was used to achieve those mileages) yields 49.15. The 52.4 tank is approx 6.7% better than that.

Rick

 

Seems strange that higher octane would produce better FE in an engine designed for 87. Higher octane fuel usually is less efficient because of all the anti-knock ingredients added and does not contain any more energy than 87. Hmmmm. Could be that there are too many variables to deal with like driving style, road/traffic conditions, etc that would also improve or worsen the FE.

 

In my real world test I didn't notice a significant benifit. The price difference for higher octane is greater than any benefit I had seen on my tests.

 

In regular cars the engine will advance the spark timing to get more power out of each stroke when you use premium gas. If your engine doesn't (or can't) advance the timing then you really won't see any difference in FE, and may even find the slow burning fuel (premium) giving you less power. If your engine has the ability to advance the spark timing it will also have a knock sensor so that if it detects a ping it will retard the timing back a little until the pinging/knocking stops.

I don't know much about the HCH engine, but if you can find out if it does advance the spark timing then there may be an advantage, but if it doesn't, then there's really no way it can take advantage of the premium gasoline, and your catalytic converter will be working overtime burning all that unburned fuel coming from the engine.

 

The HCH does have 8 spark plugs versus the normal 4, so maybe that helps burn the higher octane fuel more efficiently? Just axin...........

 

Cheaper gas burns faster and has slightly more power. Expensive gas burns slower so it will not pre-ignite in a high compression engine. The rule of thumb is to buy the cheapest gas your engine will burn without pinging. Octane ratings have nothing to do with the energy or power in gas.

 

In much agreement with Lakedude on his last post - here is a very good 'splanation of what Octane means:

http://auto.howstuffworks.com/question90.htm