My daily Prius mpg is still higher with Shell 87 octane than it has been for the previous year - in the 47-48 range. My workday drives do not allow for the higher mpgs as I'm constantly having to change speeds and climb hills from dead stops - still, long distance highway mpg is around 54 which is far higher than I've ever had before.

Incidentally, I switched my other cars to Shell. I found my 2001 Toyota Sequoia 8 cyl (135K miles) didn't much care for the Shell 87 octane gas (two tanks and no apparent change in mpg) but the 89 octane does wonders. Average mpg before was around 15 in town (17.5 indicated highway) today I drove close to 180 miles (second filling of 89 octane) and averaged 21.5 mpg indicated (highway at 70 mph, some city driving included).

I don't know if Shell gas is cleaning my injectors better than the other gas I used in town or what. I don't know if I switched back to what I was using if I would be able to maintain my mpg because my cars are running better now. I haven't been using fuel injector cleaner but maybe I need to consider doing this every few tanks.

It made me wonder what a few tanks of 89 octane will do in my Prius. Bob, have you tried 89 octane in your Prius? What are your thoughts?

 

Hi Ray,
Right now, I'm testing different brands of 87 and that survey will take a couple more weeks. Once that is done, including retesting the highest and lowest, I can look at testing different grades from the highest energy brands. But first, I need to narrow the field.

The literature suggests higher octane gas has less energy. However, it is easy enough to test if you are interested and have a long hill you can climb at 55 mph on cruise control.

To test the energy quality of gasoline, approach the bottom of the hill at 55 mph on cruise control. At the same spot, reset the the MFD consumption display and one trip meter. At the top, read the MPG and trip meter and calculate the fuel burned to climb the hill. You'll need at least three readings and average the results. Then change to the other grade of gasoline and repeat the test. This will give you a good, first order measurement of the relative gasoline energy.

GOOD LUCK!
Bob Wilson

 

Thanks for all the data, Bob! Looking interesting, so far. Please keep us posted.

 

I am too looking forward to the results. Already the preliminary efficiency diagram is really interesting.

One comment though, I always thought that most of the effiency gain would come from the ability to advance the timing, and that it would take some driving for the ECU to adapt to the new fuel. Half a tank or so. The tests I have seen in magazines used to run at least two consecutive tanks of same fuel before measuring - power, not FE of course, but still.

 

As I complete each fuel test, I update the chart. You might have to refresh the browser cache to see the latest. Right now, I'm burning off the last of the BP and will go to Citgo next.

I'm also adding fuel density. Via Ebay, I bought a thermometer equipped, hydrometer calibrated for gasoline and am waiting on 500 ml cylinder to float it in the fuel sample. I should have everything for density measurements next week and will go back and retest the earlier samples.

There are two sites, one a government research laboratory, that reports the energy density per unit mass is constant. However, the specific density of hydrocarbons, the mass per unit volume, does change. This makes sense because as the number of carbons and hydrogen atoms increase in a hydrocarbon molecule, the density goes up as does the amount of chemical energy per volume. In simple terms, denser gasoline has more energy per gallon.

Perhaps you might provide the URLs? The only timing changes I'm aware of are those required by higher altitudes.

Bob Wilson

 

Wow, I wouldn't believe it if Bob didn't say it - looks like Shell really does have an edge. I've had a hard time finding a Shell station in So Cal so I'm behind on my tests, but maybe after these results I'll switch to Shell and stay there... .

Then again what few Shells there are around here appear to be some of the higher priced stations - they're onto us!
http://www.gasbuddy.com/gb_gastemper...88&long=-118.5

 

A) I own an '04 Civic Hybrid - when the battery is low the system works a little harder to make sure there is sufficient charge. Does running a Prius on electric only lower it to a point where it declares "state of emergency" and works harder to recharge? If so are you accurately running it to that same point each time?

B) Personally I've found that my Civic is wildly inaccurate on early miles of each tank. I think I would have used more than 5 gallons to get accurate measurements. Perhaps 10 gallons?

C) Someone else mentioned inaccuracies of pumps - maybe round two of tests could use an external fuel can as an accurate measuring device?


All in all I think you're doing a wonderful job. The only difficult part is being consistent for each test. Though that would require a lot more personal time. I'm envisioning a large loop of highway / interstate around a large city with a starting point that provides gas stations for each of the brands in the test. That way transporting fuel to the starting point isn't a factor. Then pick a weekend and make laps around the city (wow, just realized how boring this would be). Probably two fuels could be tested per day - four in a weekend.

Another issue is you're using a highly efficient vehicle. If all you're testing is the fuel the tests could be run with a gas guzzler. It'd sure speed things up

 

CAUTION!!!

I'm testing gasoline that probably comes from the Gulf of Mexico area. I suspect West Coast and East Coast gasoline brands may have different refineries and feedstocks. I would strongly recommend the East and West coasters perform their own set of tests.

My recommendation, if you do not have a Graham or other high resolution scanner, is to do a controlled 'hill climb'. Find a hill with a reasonable altitude change and run. Then use your MFD and a trip meter to calculate the fuel burn at a constant speed (use the cruise control) and at a speed low enough to ensure the ICE is providing all of the power, 55-60 mph.

Bob Wilson

 

Hi,
Excellent question. My method is based upon getting the ICE rpm, torque and injector timing by using a scanner and recording the data during a controlled hill climb. I'm measuring the shaft-power from the ICE into the transaxle with fuel injector time. This is before MG2, the traction motor so no battery power is ever seen.

My Prius measurement technique avoids all of this. I'm measuring power between the engine and the transmission/transaxle and the engine fuel consumption.

Not really since I'm using the engine injector timing and measuring the shaft power. This is the functional equivalent of putting the engine running on a dynamometer.

Kinda weird when you realize a Prius with a Graham miniscanner has enough built-in instrumentation to be the functional equivalent of having the ICE on a built-in dynanometer.

Excellent questions.

Bob Wilson

 

But the efficiency of the vehicle also improves the amount of distance covered by a gallon of gas, improving the data because any significant variance is easier to find among the noise level of the data. Hoorah.