Jazsun

I have been told by a mechanic that if just switch from 87(what i always run) to 93 the computer wont know and nothing will change. He said you have to run 93 for like 3 tanks full before it realizes that you are running it. (so you cant just put in for a race cuz the comuter wont know the difference). Is this true? If so couldnt you just unplug the battery when filling w/ 93?

Also I know that 87 is actually more explosive then 93, which is why 93 is used w/ higher compression engines like ours. So is the purpose of using 93 just to stop detonation or does it actually add any poweR?

19camaro71

the only thing i can say about that is that the higher the octane raiting... the higher the temperature the air/fuel mixture needs to ignite and burn. I have however always run either 92 or 93 octane in my formula, and it runs very strong.

shoebox

I can't imagine having to reset the computer because of changing octane.

2000GTP

The 93 octane will not add power so to speak, but if you are losing power through detonation by running the 87 octane, then the 93 octane will restore what you are losing.

Alvin@pcmforless.com

Low octane mode.. resetting the batter is anothor way of getting it into normal mode.

shoebox

Is that a 93 only thing? I have never heard of it. How does the computer sense octane?

Alvin@pcmforless.com

Nope other models have it too.. I'm not sure off hand that the 94/95's have it (or if tunercat defines it really is the question)

its in a bunch of stuff though.. including LS1's. It basically says.. look we've been knocking consistantly so I assume theres cheap fuel in the car. I believe the LS1 watches the fuel level and resets itself when you fill up again. The LT1 just waits a certian period of time.

Buttercup

Looks like the '94/'95 cars have it too. From what I can see it retards the timing by 7 degrees if activated. You are going to lose fuel economy if that happens, which kind of defeats the purpose of trying to save money with the cheaper gas. I don't know what it takes to activate and don't plan on finding out.

It's a safety measure, not a cost saving measure for the owner. It takes detonation to activate it. If you constantly enjoy making your engine detonate, more power to you.

If you are really that broke that you can't afford premium fuel (which the LT1 is specifically designed for) than keep your foot out of it at all times. It won't knock at part throttle. The engine will not know the difference. Put in the premium before driving the snot out of it. 2000GTP said it perfectly!

Octane ratings are an indication of knock resistance only. It says nothing about burn rates, flame front temperatures, energy or any of that. You cannot specifically say one will make more power or burn faster than the other based on octane rating alone.

Speaking of knock, why did the LT1 come from the factory with such poor quench? What are the specs of the LS1?

shoebox

Hmm...I haven't seen anything in my 95 tune parameters to tell me it is there. I guess I can take it on faith that it is embeded in the programming somewhere or maybe it really does not exist. Not saying that some other PCMs don't have it.

There are some low octane compensation constants in the table, but I don't see that reseting the PCM would be a factor in their use.

Alvin@pcmforless.com

Just because tunercat doesn't have the table doesn't mean that its not there.

Up till this year he didn't know where the idle adder for AC in teh 93' cars was.

You can almost guarentee that there is a low octane mode in a 94-95. As its been around since the 1990 F & Y's at least and its still being used on the LS1 and LS1 based trucks.

resetting the pcm to get rid of low octane mode is the same principle as resetting the battery to clear fuel trims.

Alvin@pcmforless.com

just peeked at the 94-95 definition and hes even got it in there.

from $EE definition

shoebox

Yes, I stated that there were some parameters in there. I just have never seen any description that tells me resetting the pcm does something for them (or whether there is actually anything to reset). The BLMs, I can see reset on a scanner. I guess it is just as easy to reset the PCM or ECM and be done with it. I just like to see some proof of what is going on.

Z95m6

Learning something new everyday.

shoebox

Lol, me too, I guess.

Alvin@pcmforless.com

Low octane would be a flag held in volatile memory just like everything else.. Just like pulling the plug on a alarm clock and watching it loose the time.

Theres no perminate non-volatile memory writing or learning taking place on these computers and theres no on board battery backup.

The only time non-volatile memory is written is when you hook up under the steering column.. send a command to erase, then precede to reflash the computer.

Theres fuel and essentially spark learning happening all the time.. but just as soon as you unplug that sucker it looses its memory just like when the power goes out and your wondering why the alarm clock didn't wake you up.