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Diablo Tune with 87 Octane?

Predator support for GM gas vehicles

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Posts: 1147
I was careful when choosing my words. The stock tuning does not benefit from using premium fuel. There are very few vehicles that are designed from the factory to re-tune the engine for premium fuel. I never said to use premium fuel with the 87 octane tune. I was referring to your claim that the engine does not "require it" and chemical knock retard. When you increase your timing and lean out the fuel mixture, you are essentially increasing your combustion pressures. Pressure is related to temperature and volume. Increasing compression reduces the volume and increases temperature and pressure. Increasing temperature and pressure (by adjusting the fuel mixture and timing) has an effect similar to increasing your compression (like piston changes or milling your head, but to a lesser extent).

The first thing you need to do before adjusting timing is to adjust your fuel trims as described in the stickies on this forum. After that you can raise timing and monitor your logs. You can try to use the butt dyno to gauge increases in performance but that may not be very accurate.


Posts: 40
concoursd wrote:
I was careful when choosing my words. The stock tuning does not benefit from using premium fuel. There are very few vehicles that are designed from the factory to re-tune the engine for premium fuel. I never said to use premium fuel with the 87 octane tune. I was referring to your claim that the engine does not "require it" and chemical knock retard.


You said that running premium is of no benefit unless your vehicle is tuned to run it i.e. advanced timing etc. I am simply agreeing with this and taking it one step further by questioning why should I run premium with the diablo tune when it is less or the same spark advance as my factory tune. I mean exactly why does the diablo tune benefit from running premium? I have read...you should run 93 with the diablotune because WOT timing is advanced alot....is it?

And how exactly are we leaning out the fuel mixture? We are supposed to adjust the LTF's by telling the ecm we have a different size injector than we actually have? But that is just so the ecm does not have to work so hard to correct the LTF's, right? So then when it calculates for PE it is using a false set of values? Then we are supposed to adjust PE to 12.5 to 13.

If I cannot feel a difference, then exactly what does this thing do again?

Post Mon Mar 22, 2010 10:59 pm

Posts: 40
Here is my latest log. It is the diablo tune, -1° in all rpm ranges, LTF's adjusted -3%, burning 87 octane no additives @ 2,000 feet above sea level 46°F.
Attachments
Diablo Tune LTF Adjusted 3-22-10.csv
(1.26 MiB) Downloaded 27 times


Posts: 1147
KDIXER wrote:
concoursd wrote:
I was careful when choosing my words. The stock tuning does not benefit from using premium fuel. There are very few vehicles that are designed from the factory to re-tune the engine for premium fuel. I never said to use premium fuel with the 87 octane tune. I was referring to your claim that the engine does not "require it" and chemical knock retard.


You said that running premium is of no benefit unless your vehicle is tuned to run it i.e. advanced timing etc. I am simply agreeing with this and taking it one step further by questioning why should I run premium with the diablo tune when it is less or the same spark advance as my factory tune. I mean exactly why does the diablo tune benefit from running premium? I have read...you should run 93 with the diablotune because WOT timing is advanced alot....is it?

And how exactly are we leaning out the fuel mixture? We are supposed to adjust the LTF's by telling the ecm we have a different size injector than we actually have? But that is just so the ecm does not have to work so hard to correct the LTF's, right? So then when it calculates for PE it is using a false set of values? Then we are supposed to adjust PE to 12.5 to 13.

If I cannot feel a difference, then exactly what does this thing do again?


There are two different diablo tunes being conflated together. Your questions posed in prior posts I believe are pointed to timing settings when running the stock setting vs. 87 octane diablo tune. Neither of those tunes would warrant premium fuel.

The premium fuel should only be used when using the premium fuel tune.

In regards to LTFT, users notice significant mileage improvement and performance response when dialing-in the injector slopes. You would think otherwise but it works.

Furthermore, the PE fueling is a commanded setting so the fuel trims only act as modifiers to the PE values. The PCM is "guessing" what is needed during PE by adding/subtracting to the commanded/desired a/f ratio set. Adjusting your injector slope and PE values will help to get the most out of the engine regardless of fuel octane used.

You never tune timing settings until you have dialed the fuel settings because a excessive lean condition can cause spark knock under load so your timing adjustments would be made to correct a symptom caused something else.


Posts: 40
This whole topic is about using the Diablo Tune with 87 octane gas. I have stated several times that the timing in both the diablo (or premium gas) tune and the 87 tune have less spark advance than the factory tune. My main question is why run premium gas when there is no TKR.

I have read that technically you should use the lowest octane you can run without KR or detonation. There is no performance gain with running a higher octane than what is warranted, right?

I can honestly tell a difference between the diablo tune and the stock tune performance wise. But why do I need to run premium unless I am getting spark knock?


Posts: 1147
I would not run premium fuel with the 87 octane tune. I would just do some datalogging and tweak a little more if desired using the neat dslogredux app that is available from dslogredux.com. they take donations.


Posts: 40
LOL

Would you run 87 octane fuel with the diablo tune as long as you are not getting KR...?

Are you messing with me...LOL?

I am running 87 octane fuel with the diablo tune just to be perfectly clear.


Posts: 1147
not messing with you.

There are two different tunes in the Predator for trucks. an 87 octane tune and a premium fuel tune.

Obviously you would use the 87 octane tune when running 87 octane fuel and premium fuel with the premium fuel tune. If you are not getting any knock retard, and you dont hear any knock then you can tweak the tune by advancing the timing accordingly. Every engine is different and some are more sensitive to knocking than others.


Posts: 15
KDIXER wrote:
LOL

Would you run 87 octane fuel with the diablo tune as long as you are not getting KR...?

Are you messing with me...LOL?

I am running 87 octane fuel with the diablo tune just to be perfectly clear.


concoursd wrote:
not messing with you.

There are two different tunes in the Predator for trucks. an 87 octane tune and a premium fuel tune.

Obviously you would use the 87 octane tune when running 87 octane fuel and premium fuel with the premium fuel tune. If you are not getting any knock retard, and you dont hear any knock then you can tweak the tune by advancing the timing accordingly. Every engine is different and some are more sensitive to knocking than others.


Actually the tune referred to as "premium fuel tune" is actually named Diablo Tune.........So it looks like the answer from concoursd is 87 = 87 and Premium aka Diablo Tune = 91+.......But I am curious too, why the higher octane when no KR is occurring when logged?

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