dual octane tuning

**ONE04FX4** · 02-09-2004 06:22 PM

The dual tuning is nothing new or invented. The pcm has two tables, the low octane and the high octane table. For those who use the high octane gas, you can benefit from having two high octane tables, this is accomplished by copying the hi to the low. For those who run low octane, both tables are alterered for better performance, but you're not paying for "daul tuning" it's already built in. The tuner is just making sure you'll notice a performance increase whether you're running good or bad gas.The pcm will switch between the two tables based on how much detonation is detected. Keep in mind the pcm is not "dual tuned" there's not such thing, lol, all it is , there are two tables, one protects you from detonating your engine to death and the other is used when no detonation is detected.

**01Thunder** · 02-09-2004 06:41 PM

do you have that Lance?
If you do than I'm gettting it too!!!

**ONE04FX4** · 02-09-2004 07:43 PM

no 01 thats the point. we all have it. its built in from gm.

**01Thunder** · 02-09-2004 09:21 PM

as long as we both have it.
i'm still lagging behind in the cam area

but one day that will change

**BigKID** · 02-10-2004 01:10 PM

Although you are correct about the two octane tables in the pcm, you are completely misled on Hypertech's tunning methods. Hypertech dosnt touch the low octane table. All their tuning is done in the HOT. The 87 oct tunning only adds 2* where as the 91 oct tune adds 4*. That my friend is the 'Dual Octane Tunning Truth'.

**Bandit** · 02-10-2004 04:14 PM

A few questions...

So if the vehicle in question was designed to run most efficiently on 87, does that mean the high octane table is actually 91 octane? Or just anything higher than 87? What about the low table? How does the pcm calculate the octane level in the gas? A knock sensor just detects knock, right? What is knock? Pre-ignition or detonation? What's the difference? Do we really care about the octane level? What does the pcm do to adjust to oxygenated fuels and seasonal blends?

Any ideas?

Bandit!

**GMCwantsLS1** · 02-10-2004 06:10 PM

Originally posted by Bandit@Feb 10 2004, 04:14 PM
A few questions...

So if the vehicle in question was designed to run most efficiently on 87, does that mean the high octane table is actually 91 octane? Or just anything higher than 87? What about the low table? How does the pcm calculate the octane level in the gas? A knock sensor just detects knock, right? What is knock? Pre-ignition or detonation? What's the difference? Do we really care about the octane level? What does the pcm do to adjust to oxygenated fuels and seasonal blends?

Any ideas?

Bandit!

Hahaha Bandit I wonder if this will turn into a big debate again! One could write a whole book (or at least a chapter) on those thoughts.

**BigKID** · 02-10-2004 06:28 PM

To the best of my knowledget the pcm uses the high octane table till it scences 5+ degrees of constant knock, weither it be detonation or false knock, then switches to the low octane table. It will stay in this table till 7+ gallons of gas is added. So no, the truck has no way of knowing what octain fuel is in it but bases the tables on knock values. So... maybe the tables should be labeled 'good gas' and 'bad gas'. ???

However, I believe Bandit already knew the answers to his own questions already.

**Bandit** · 02-10-2004 08:39 PM

NOW you opened up a whole other topic....Fuel level! Does the pcm still change tables at fuel levels over 80% or below 20%? It makes a difference....

Bandit!

**BigKID** · 02-16-2004 02:57 PM

I have wondered this as well but havent been able to get any conclusive evidence via my autotap logs or track times. Why dont you enlighten us?

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