I was reading an earlier post about what octane to use in my car, and the bottom line seemed to be that using any gas with a higher octane than 91 was pretty much a waste.

Up to this point, I had been using 93 since I bought the car because it had been the only stuff available higher than 89. I decided to go ahead and fill a tank full of half 89, half 93, (to get 91) and lo and behold my mileage increased a few mpg as measured at my next fill-up.

Anyway, here's the question. People had explained that the higher octane would only be useful with advance timing and/or altered fuel maps.. that on a stock motor it was a waste. Is it possible to tune my motor to use the higher octane? Swiping my card at the pump twice is kind of a hassle, and I wouldn't mind spending a bit more if it wasn't going to waste.

I have only a basic automotive knowledge, but am pretty good mechanically. Is this idea even feasible, or am I way off? Is it something I could do myself?


Cliff's Notes:
Can you (or better yet, I) tune a stock motor to 93 octane gas rather than 91?

 

yes take your car to a mechanic or if you know how to use a timing light advance your timing, then you can use high octane gas. Or take your head off your engine(downtime) and have the head milled to raise compression then use high octane gas. but with gas prices rising I dont understand the logic just be happy you dont have to use 93 octane on a daily basis.

 

If you advance your base timing to 16-17 degrees before top dead center you will get back that fuel mileage and gain some power too. I know some people think that having a resistor on your intake air temperature sensor is cheasy, but I have used one on my prelude and it will allow your car to run some advanced timing curves in the mid range because your computer will believe that the incoming air is colder. I would run a 15k ohm resistor on one or the other of the two wires coming out of your intake air temp sensor.

The sensor is located on the driver's side of your intake manifold down next to the side of the strut tower. Just a thought....

 

why 15k ohms specifically? personal experience?

are there any negative to advancing your timing aside from being "stuck" at this higher octane level?

thanks

 

so what ur trying to say is that using over 91 octane is usless on a stock prelude?

 

if your car is a 5th gen you can't advance the timing, you can however on a 4th gen.

The 5th gens have a timing map, much like a fuel map, your ECU is programed for max timing performance over the RPM / engine load map, and the only way to adjust this is to get a new ECU. 4th gens don't have a timing map so you can bump the timing up by rotating the dist.

And yes, it is a waist to run higher octane than what the car needs.

 

If the ECU thinks the air is colder i.e. denser, it'll add more gas. How is that good for fuel economy?