I have a 90 GTU and I have looked at the search, and I just wanted to confirm that using 87 octane on an NA is okay if not better than using 92 premium. Am I correct in saying this? Thanx in advance.

 

Many people have been using 87 octane in NA models, with great results.

However, IMO it depends entirely on the quality of the gas.

For example, 87 octane in the midwest, does not have the smog reducing O2 clean air additives that California and [as I understand] New York gas has.

Again IMO, these additives screw with how the gas is burned and how the hydrocarbons are released, and I feel a degrade in the performance, so that the car appears to be running on 86 or 85 octane gas. Well below the Mazda suggested min. of 87 octane on the NA.

So without any lab proof, or dyno proof; in California the lowest that I run is 89 octane in my NA. It might be all in my head, but my RX seems to run better using 89 or better and for the 3 or 5 cents a gal that’s less than a $1.00 per tank for that perceived extra.

 

The n/a 13b was designed to run on as low as 83 (or was it 80? someone?) octane.. 87 is more than enough. If you run higher octane, it's harder to burn, therefore produces less (not MUCH less...but still less) power, and burns less clean. This translates to worse emissions and more crud in everything..

Of course, the difference between 87 and 89 is so small, it's basically unnoticeable.. except 89 is more expensive..

so unless you've REALLY, REALLY modded your n/a (and some say even then), you should run the lowest stuff you can!

gas quality is another issue...

-Tesla