Running 87 octane with ignition timed for 91

[Rembrant]

Hi folks,

Ok...I think I'm all sorted out on the taller 5th gear option, but my next interest is in an ECU flash. Of course the ECU flash is for more HP/TQ, but they also advertise "Increased Fuel Efficiency".
I asked the rep today about what could be expected for an increase in MPG...not expecting much mind you, but they didn't have much info to give.
The ECU flash will make it more fuel efficient, but the majority of people that go this route are not looking for efficiency...they want more power, and they use it. In the end, he said that if I drove it easy (like I am now), he guessed at gains somewhere in the 6-10% range.

However, since the bulk of the ECU flash benefits are in the ignition timing...I would have to start running 91 octane fuel....or 93 octane with the more advanced kit. (93 is not available where I live, so it's not an option).

Just curious I guess what would happen if I were to try running my usual 87 octane when the ECU ign timing is advanced for 91 octane? Would it simply have less power, or would it more than likely ping like a mofo?

I guess I'll check the timing advance with the Scangauge with the stock ECU, and then see what it is after the ECU flash to compare (before trying to revert to the el cheapo 87 octane).

Thoughts? Comments good or bad?

Rem

[redpoint5]

Someone would have to be an expert of both the ECU reflash and your car to give an educated answer.

My car specifies 91 PON, but operates without issue and without any noticeable change in fuel economy with 87 PON. I'm just barely able to perceive lower torque at high loads running regular gasoline.

On the freeway, the car will advance ignition timing 39 degrees on 87 octane, but will run 40 degrees on anything above 87 octane.

I don't know what you drive, or how the reflash is programmed, but modern ECUs should detect pinging and retard the engine.

[ECONORAM]

I can't speak to your vehicle, but can give you some information on my RAM. When I was in northern Utah (4700 ft elevation), the low grade at the pumps was 85 octane. The truck's factory tune would run on it, but when I installed an 87 octane tune from Superchips the engine would ping on 85 octane. I had to run the mid-grade, which was 88, in order to run the 87 tune. I've never tried to run the Superchips 91 tune on 97 octane. In fact, the folks I've chatted with do not recommend using 87 octane with the 91 (or 93) tunes...
At light throttle settings I've seen 39-40* advance with 87 octane, and 45* with 91 octane.

[freebeard]

Your options for fuel additives range from acetone to nitromethane.

...from doing nothing to 'blowed up real good'. Isn't it a shame you can't get Hadacol anymore.

[Cobb]

The 2nd gen insight will run on moose piss, but loves 93 octane. You notice a boost in performance and mpg, but the mpg boost is not cost effective. For performance and throttle response, I think it is worth the extra.

Its a mixed bag, too much ignition adds nox to the exhaust. You can use more fuel to help reduce ping, but there goes your mpg.

[serialk11r]

I'd be pretty surprised if your ECU flash actually did much, because most tuners only know how to add power. That's the impression I get from reading people's posts on car forums.