Low Octane table

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May 31, 2011 | 07:17 PM

eboggs_jkvl

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From: Jacksonville Florida BWO Dayton, Cincinnati, Bloomsbury NJ, Cincinnati

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Low Octane table

Like a lot of us, I have the aftermarket tune in the car and it has the high octane table the same as the low octane one. Well, in the advent of a worst case scenario and I am forced to load up with low octane regular, what would be a good low octane table to have in my tune?

I mean, if I take the high octane table and reduce the entire table by what percentage or perhaps pull x number of degrees for the entire table to become the low octane table. What would be a good number or % to use?

Elmer

May 31, 2011 | 07:49 PM

REVAK

Drifting

Joined: Apr 2006

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From: Ambler Pa.

Quote:

Originally Posted by eboggs_jkvl

On pre computer engines, [ distributor ], on a small block tuned for premium, [ 93 equivalent ], we could run them on reg. [87] by retarding the timing 2 to 4 degrees. I'm guessing maybe 10% or so may work on your LS2. A tuner could tell you better. I hope this helps, most all of my experience is from the points and condenser days. Yes I know that is sad.

Jun 1, 2011 | 07:19 AM

seevi

Burning Brakes

Joined: Aug 2008

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From: Oro Valley AZ

Quote:

Originally Posted by eboggs_jkvl

Have the stock low octane table reinstalled to be safe.

Jun 1, 2011 | 11:02 AM

Mez

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From: Austin, Singapore, Kuala Lumpur, Houston, Dallas, Hong Kong, Elgin, etc.. Texas

I see many tunes that have them set identically but I really don't agree with it. These tunes basically make the PCM less adaptive to different conditions. When these two tables are the same, the PCM totally relies on the knock sensors and related tables which is like making adjustments with an axe instead of a scalpel.

I compared a stock LS2 High Octane and Low Octane tables. In the .15 to .32 g/cyl cells, the two tables are identical at all RPMs. This is at idle and light throttle conditions such as low speed cruise.

As you increase engine load above .32 g/cyl, the low octane table cuts ignition advance 1° every g/cyl line until a max of -10°.

Just whacking the table with a flat percent reduction cuts the higher timing values which are the lighter throttle areas more than the lower values which are the heavier throttle areas and is exactly the wrong direction. You may want to just do the same as the factory but only down a max of -5° because you have a E-Force S/C. The E-Force tune already has timing backed down quite a bit, so -10° may be near zero at WOT.

Last edited by Mez; Jun 1, 2011 at 11:10 AM.

Jun 9, 2011 | 04:28 PM

BluV

Instructor

Joined: Jan 2008

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From: Denton Texas

St. Jude Donor '09-'10

Quote:

Originally Posted by Mez

I see many tunes that have them set identically but I really don't agree with it. These tunes basically make the PCM less adaptive to different conditions.

It seems lazy to me - but I understand the business side of it. I kept both of my tables - but I did my own tuning. Best scenario - fill up with low octane, and tune again. Then you can keep both tables fully optimized. Overwriting the low table with the high table values is pretty cheesy - and only for those that never travel more than 1/2 tank of gas from the home base! But truth is, this is probably the way 98% of tuners do it or so it seems.

Mez has great advice above. It really depends on your mods (sorry, did not look at your profile). If it is headers/intake only, the low octane table is easier to fudge than if you have cam/blower/etc.