Higher octane fuels have a higher activation energy required for combustion therefore actually have less potential energy than lower octane fuels.

You can't reduce MPG to which gasoline has more energy per mol or whatever. Waaaay to many variables involved. Just do the test and see what taste your isuzu prefers before making a decision on what octane to run.

I have a 99 Trooper, my manual says 87 minimum and that's what it gets. We're at about $2.85 a gal. here in NJ (for 87). As was just mentioned, higher octane burns slower and is less explosive. This is why it is better for high compression cars that run 10:1 like the trans am i had, even 89 made it ping. withouth high octane it is more prone to detonate. however, my trooper has a 9:1 compression so 87 actually matches the compression ratio better.

The contradiction is that higher octane usually still feels like the car has more power, maybe because they have more ethanol which releases more oxygen.

Point is, run 87 unless it pings, (manual says a little pinging is fine!). I'm sure your mileage will vary much more with driving habits than the little it MIGHT vary with different octanes.

Just my opinion.

Superchip actually had different brands of gas with all of their different additive packages tested by a third party lab.

They had posted the top stations that had the highest BTU's per gallon, which should net you more miles per gallon.

Amoco, Citgo, Texaco and Shell were the top few.

BP and Exxon were two of the worst, as far as BTU's per gallon.

This was of course done for their test purposes in order to get the highest numbers out of their chip mods.

Man, you guys are way mistaken here....
All grades of gas have the same amount of stored energy. Octane has no bearing on anything but the fuels resistance to detonate. Once you detonate, all gas releases the same amount of energy. Octane is an additive, not a fuel. Higher compression and higher RPM engines require higher Octane because 1. they generate more heat, which can cause pre-detonation, and 2. If you pre-detonate at 8000 RPM, then your killing your engine. The speed at which the fuel burns depends on the combustion chamer, the fuel spray, and the spark, not the grade of gasoline. Also, it is well known that running E85 in your engine will give you less MPG becuase ethanol stores less energy than gasoline. Some engines can compensate for this lack, i.e. add more fuel to the engine, making the switch "more transparent" but I've never heard of somebody saying ethanol gave them more power. Maybe your thinking of methanol?

I personally tend to run regular when it's nice and supreme when it gets closer to freezing. The supreme seems to pay off when it's colder - quicker warm-ups, better mileage, and no need for gas line antifreeze.... unless you're in New Mexico where you just don't need gas line antifreeze .... <;-D
I found that full synthetic oil helps and my K&N air filtermade a difference too.
But the biggest difference I notice is when I put injector cleaner in my tank every so often. The following couple of tanks are noticably better.
... the ethanol acts kind of like an injector cleaner - I'm told.
But while the injector cleaner can be helpful to sensors - the ethanol is not supported by all manfucturers' warranties.

Not that I think anyone here is worried about their warranty. <img src="/forums/images/graemlins/smile.gif" alt="" />

on this topic. I went from the open air K&N air filter. Cleaned every oil change and swithched back to the stock airbox just last week. I have gained so far 80 miles to the gallon per tank. THat took me from 14.3 miles to the gallon to 16.9. the only other change that i made to the truck was switching off of a full synthetic oil. I was pissing money away just burning the mobile one oil. Will be doing a fluxh change this week after the rain stops to make sure I got all the synthetic oil out.

I dont think that the isuzu product engines were made for the open airfilter like K&N. Just my 2 cents though

I wonder how much climate and elevation play into this ....
I'm in Alberta where there is two seasons - winter and construction. It's usually fairly dry and the altitude is about 700 metres.
I guess everyone's success with different things depends on a number of factors.
My 2.7l suzuki V6 liks the mobile and the k&n
the lil ford 2.0l ztec likes it as did my 4ze1 trooper -before I began the restoration.
I've never driven in Virginia though, so I can't say what would happen in your climate, elevation and humidity. <img src="/forums/images/graemlins/cheers.gif" alt="" />
A clean, brand new air filter will always improve mileage. A good investment before a long trip. <img src="/forums/images/graemlins/smile.gif" alt="" />