It's hot, VERY hot today here in San Jose, so this afternoon instead of roasting at home I decided to do some serious driving

I started out driving an easily repeatable roughly 1 hour long drive, cruising at 70MPH, with the last of a tank of 91 octane gas.

Then with the very last bit of that tank I weighed the truck (4980lbs with me) and then did three 0-60 runs with my GTech Pro Comp.

Then, with the empty light on and DTE at 25, I filled up the tank with 87 octane (17 gallons worth). Repeat the trip to the scales (5060lbs) and test 0-60 runs with the GTech, and lastly drive the same hour long test loop cruising at 70mph.

The results? HP wise, it's identical, measuring 194HP at the wheels and 0-60 times of roughly 7.4 seconds (yes that HP number is low, my GTech always reads low, that's okay, the before and after comparison data is still valid and it was virtually identical).

The MPG? 91 octane clocked 22.7MPG while the 87 only got 21.6MPG. If you do the math, and assume a $.20 difference between 87 and 91, gas would have to be over $5.00 a gallon for there to be any economic incentive to running 91.

After putting in the 87 I did occasionally hear some brief pinging when in transient partial-throttle situations, but after a few minutes the ECU seemed to have compensated properly and I didn't hear any more for the rest of the evening's testing. If the detonation comes back and is at all persistent I'll move up a grade to 89, but there really doesn't seem to be much reason to run 91 beyond it giving you that warm fuzzy feeling inside from spending more money to burn slighly less gas (one gallon less per tank roughly).

Next time I have a toasty afternoon to kill maybe I'll try 100 octane for giggles and see if the timing maps have any headroom to take advantage of it

good write up.
its guys like you that take the time and energy to prove or disprove many of these fuel issues.

Thanks for the testing -- it's great to know your findings.

I've haven't done the level of testing you have, but seem to be having similar results in my unscientific tests.

I've done some highway testing on 87 vs. 93 and don't see any noticable difference.

I do a fair amount of boat towing with mine, before I take the boat out I try to plan ahead and not fill up for a few days, getting down to 1/4-1/2 a tank if possible and then fill up w/ 93 because I know the truck will be under extra load, but other then that I run 87.

I just changed from the factory fill oil to Mobil 1 5w30 last week (3414 miles) and have driven about 300 miles since then. The truck is more smooth/quite and I seem to have gone from about 15.5-15.7mpg city to 15.8-16.1 mpg city.

Yeah, when I switched my Murano over to fully synthetic lubes I saw around a 1MPG improvement. When I finally get to 10K miles on the Path I'll do the same again and see how it goes (changing the motor oil, transmission, transfer case, and both diffs over to synthetic).

I also have a rear spoiler I need to get installed, should be amusing to see if there's any change in MPG with it

Isn't 100 octane race gas leaded?

That wouldn't be good would it?

No, 100 octane race gas is usually unleaded, you can actually buy it at the pump at some special Unical 76 stations around here. Aviation 100 is leaded, and also 110 race gas is also leaded.

Cool.

The Meijer grocery store here in Lexington, KY used to have a kerosene pump out away from the other pumps. I noticed this weekend that it had been replaced w/ a newer pump and had a Race Gas sign over it, I was pretty far away but thought it said 100oct leaded race gas. I'll check next time I go by there. Guess it could have been 110 or unleaded (will also check price).

We aren't really close to any major tracks. They did just put in a Harley dealership, Porsche dealership, and a general bike shop (all brands, specilizes in high end go fast bikes) all within sight of the Meijer though. I guess some of the modified bikes could cause demand?

Hm, interesting. Kinda crazy to build any bike or car motor for the street that requires 100 octane gas, but eh, who knows =P.

One of the amusing things I've seen here is that the cost of 100 octane gas hasn't gone up much over the last few years. It's still around $4.50 a gallon, so in proportion to 91 octane the 100 has been getting cheaper and cheaper

It was leaded 110oct at $4.49 9/10 per gallon

Wow, that's cheap, 110 runs over $5/gallon over here in CA.

And no, don't put it in the Path, the lead will kill the O2 sensors.

Nope, won't be putting it in my Pathfinder.

However, my modified '78 Bronco's 400 V8 w/ no cats might like to try it.

RacerZX,

Wow! You're getting way better MPG than my truck. I'm yet to do actual calculations at the pump vs. the read on my odometer, but the computer is telling me that I'm roughly getting somewhere around 15.5mpg. I've had two oil changes so far (at the dealership), and I have yet to put in synthetic. Unfortunately, I don't have the ability to do my own oil changes, otherwise I would have started using it by now. I'll have to check to see what the upcharge is for Mobil 1 (or the like). My truck doesn't get driven on very long trips that often either(mostly around town kinda stuff). I'm glad you did the comparison with the octanes, cause that was one thing on my mind that I hadn't tried yet. Thanks!

Well, if it makes you feel any better, my around town MPG is about 16 as well, depending on how much I can restrain my right foot.

The tests above were done starting at 70MPH on the freeway, cruise control on, and then resetting the MPG gauge at the same spot. So even the gas to accelerate up to 70MPH isn't factored in, so don't expect to get those numbers unless you've got a long road trip ahead of you.

Cool! Call me an idiot, but I didn't realize you can reset the MPG gage. I guess I need to read my owners manual a little more thoroughly! I was wondering why it didn't change much on some of the longer road trips (I'm guessing it's been calculating on the 6000 miles the truck has overall, based on your last comment that you can reset this crazy thing).

humn... Im here in staten island ny, and I also do alot of around the town driving. My mpg gauge has been around 13.5 with the ac on. I drive rather cautious, not too heavy on the pedal. On a recent trip to atlantic city (2 hours highway) I was at 20 mpg. Maybe the 13.5 local will go up once the summer is over, and no more ac. thanks