I finally got my numbers from real world driving comparing 89 vs 93 octane.

93 = 20mpg
89 = 24mpg

Maybe I need to do some more road tests to get a better average but I'm just surprised at the difference. Which do you put in your Max? Any problem with sticking to 89 even though the sticker inside my gas door says to use Premium fuel for "Maximum Performance?"

 

DUDE you can't compare MPG like that, there's way too many variables.

 

better way to compare:

run your car for a week then go to the track with 89 then do the same with 93

 

I decided to put 87 in my car at the last fill up and there is noticeably less power (ECU pulling the timing). Probably wouldn't recognize it as a daily driver but still.

 

You'd need to track mileage for about a month on each octane level and average several tanks to get a better picture. Please don't tell me this was just a tank each. Yeah, way too much noise and variability.

 

I win . 27mpg on 93.

 

on stevtec.

you should run couple more tanks to prove that your theory is reasonable. one tank of gas doesn't represent anything.

 

BTW I averaged 29.5 mpg on 93 octane on a road trip of about 800 miles once. I hit 31 in one direction and 28 on the way back. Stock 99 5spd, one passenger, some junk in tha trunk too. Unfortunately I didn't make the same trip on 87 to compare. Oh and tires were cranked up to 36 psi also.

 

A friend an I just made a trip in his 89se 5spd, avg. speed of about 85mph, a few bumps upto 105-115. Plus a few runs down the drag strip 529miles on the odo with 1/8tank left on the tank when we pulled up to the gas station. 87 octane. Full interior + tools and crap. Plus him and me in the front. Not sure of the tire pressure. Only mods are CAI and no muffler.

 

I deliver pizzas so 90% city miles

I'll be sure to track my progress from now on to get a better average.

 

im a third gen owner and i can only run 93. even before i got the ecu (and other mods) if i ran under 93 i lose mpg. not a huge difference but the car ran like crap. the most i ever got out of my car was approx 36 mpg (all highway miles) but now i avg 20 and with the system more like 15 hehe. with a 5000 WATT RMS amp and a 120lb battery my alternator makes me eat soooooooo much more gas lol.

 

He must have the optional 30 gallon fuel tank.

 

87 octane is actually easier to ignite, as the higher octance (93) resists combustion due to the cylinder pressures better. In my old VG30 89 gxe I got better mileage with 87 octane than with 93, but the lower compression and less efficient coil/dist/wires ignition were surely the reason behind that. It was not up to the same ignition duty as the newer 10:1 and coil/plug of the VQ. My 98 I30t with a full exhaust runs very weak on 87 and although the gas mileage difference is negligible between 87 and 93 the extra $3 per tank is well worth it in available power and pep.

 

Very well stated.