There really shouldn't be in real difference in MPGs between 91 and 87 unless you spend a lot of time above 4000rpms or under high load situations. Lower octane fuels burn easier and as long as you're at lower rpms that don't create excessive compression chamber heat and doesn't kick in the knock sensor, 87 octane should be fine. Now if you're a spirited driver, 87 octane isn't for you because you'll see a 15whp+ loss above 5000rpms.

One thing that REALLY impacts highway mpgs is wind. If you live in a windy area, you can expect cross and head-on wind will impact MPGs by 15 to 20%. I've seen wind impact my SUV/truck rentals by 30% in excessive wind (constant 20mph+ wind).

 

can you use a higher octane in a stock g35? like race gas

 

I really dn't think the people reporting these gas mileage are exactly Driving Ms Daisy. Oh well, just trying to keep it real. I'm still happy with my car.

 

The sticker octane on pump is not very reliable since the marketing department selects the stickers. The exact same product can be called 91 or 92, or 93 depending on altitude of city............lower [sealevel cities publish lower octane whereas say in Atlanta the effective octane rises].

Octane is randomly tested at refinery to meet their minimum standards, but doesn't account for any loses from transport or blending at the tank farms or time dependent octane losses.

Obviously E10 has a lower BTU per gallon than conventional so it takes [2.6-5%] more E10 to cover the distance.

 

Wouldn't the numbers also differ due to certain mods?Just throwing my 2 cents.

 

In the most recent Car and Driver, their long term Altima with VQ35 saw significantly lower mpgs when staff accidently filled up with regular. I found that pretty interesting.

 

Based on the results in this forum I estimated my 87 gas milage to be 6.5% less. That would make my cost per mile for 91 to be 18.4 cents per mile and 87 18.9 cents per mile. This shows its cheaper to use 91.