Diablosport 87 tune

[m1dn]

Been running Diablosport 91-93 performance during last winter and summer.

Now with winter approaching i realized i don’t really push the pedal anymore cause well, it will be sketchy.

So i guess the question is, is it worth running 87 tune with 87 fuel for the winter or it will just make the engine run wrong and make shit brake faster?
2008 6.2, no dod/afm

 

[Marky Dissod]

question is, is it worth running 87 tune with 87 fuel for the winter? or it will just make the engine run wrong and make shit break faster?

A proper '87 tune', by definition, cannot make the engine 'run wrong' with 87, or 89, or 91, or 93 octane. No worries.
A schidty tune, on the other hand ...
(Using lower octane fuel with a higher octane tune is NEVER recommended, even when it is allowable, which is not always the case.)

A proper 87 tune will cost some power, may cost 2 or 3MpG, and may get a wee lil bit more carbon buildup in the engine.
If you trust the tuner and his tune, no worries.

Can't say for sure switching to 87 octane and losing a few MpG is worth it?
Depends on the price difference between 87 & 91 over there.
(I personally run an 87 tune because 91 costs nearly $1 per gallon over 87 in NYC.)

 

[m1dn]

A proper '87 tune', by definition, cannot make the engine 'run wrong' with 87, or 89, or 91, or 93 octane. No worries.
A schidty tune, on the other hand ...
(Using lower octane fuel with a higher octane tune is NEVER recommended, even when it is allowable, which is not always the case.)

A proper 87 tune will cost some power, may cost 2 or 3MpG, and may get a wee lil bit more carbon buildup in the engine.
If you trust the tuner and his tune, no worries.

Can't say for sure switching to 87 octane and losing a few MpG is worth it?
Depends on the price difference between 87 & 91 over there.
(I personally run an 87 tune because 91 costs nearly $1 per gallon over 87 in NYC.)

How about the other way around, running 91 with 87 tune as a leftover before refilling, should be fine right?

I’ll retest on the weekend again, but somehow truck felt much smoother on a 87 tune, especially in idle

 

[Marky Dissod]

Using 91 or 93 octane fuel in an engine tuned for 87 octane, even if it's a bit of a waste of money, is far safer than the reverse.

 

[Geotrash]

Been running Diablosport 91-93 performance during last winter and summer.

Now with winter approaching i realized i don’t really push the pedal anymore cause well, it will be sketchy.

So i guess the question is, is it worth running 87 tune with 87 fuel for the winter or it will just make the engine run wrong and make shit brake faster?
2008 6.2, no dod/afm

In my opinion, there is no tune that will be truly safe to run that engine on 87 octane fuel. The 6.2L in this generation has a 10.5:1 compression ratio. There are lots of videos on Youtube with 6.2's ruined by 87 octane gas under high power situations, like towing, accelerating under full power to merge, etc. The knock sensors are effective, but only to a point. The '07 XL Denali was originally tuned to run on 87 to differentiate it from the Escalade, but with a loss of power, as Marky illustrates. But they did away with that tune in subsequent years. My guess is because they couldn't guarantee that the engine wouldn't eat itself under high power settings.

 

[Marky Dissod]

In my opinion, there is no tune that will be truly safe to run that engine on 87 octane fuel.

In any decent tuner's EXPERIENCE, regardless of the engine's static compression ratio, there is a perfectly safe 87 octane tune ... that cannot make as much power / torque as the 91 octane tune.

The 6.2L V8s ruined by 87, were doing HIGH LOAD stuff that no one should ever be doing using 87 octane.
(Geotrash, when you used the phrase 'high power', you likely meant 'high load').

Say a 6.2L V8 (L92, L9H, L94, L99) makes 400 horses and 400 torques, on 91 octane.
In the car, a good tuner MIGHT be able to achieve 375-380 horses and torques, on 87 octane, IN THE CAR, FOR THE L99, after a few revisions.

L99 CARS weigh at least 1000lb less than a truck / suv with an L92 / L9H / L94.
L99 CARS will never tow twice their weight.

The same tuner would be wise to aim for 365-370 horses & torques in an suv using an L92 / L9H / L94.

 

[Marky Dissod]

GM kinda makes the case for me, actually.
Compare the 6.0L LS2 V8 to the 6.0L L98 / L76 / L77 V8s.
400 horses and 400 torques on 91 octane for the LS2.
360 horses and 375 torques on 87 octane for the L98 / L76 / L77.

A good tuner can free ten more peak horses from an L98 / L76 / L77 on 87 octane, but will have a tough time freeing ten more peak torques.
Five more torques seems more likely.

 

[Geotrash]

In any decent tuner's EXPERIENCE, regardless of the engine's static compression ratio, there is a perfectly safe 87 octane tune ... that cannot make as much power / torque as the 91 octane tune.

The 6.2L V8s ruined by 87, were doing HIGH LOAD stuff that no one should ever be doing using 87 octane.
(Geotrash, when you used the phrase 'high power', you likely meant 'high load').

Say a 6.2L V8 (L92, L9H, L94, L99) makes 400 horses and 400 torques, on 91 octane.
In the car, a good tuner MIGHT be able to achieve 375-380 horses and torques, on 87 octane, IN THE CAR, FOR THE L99, after a few revisions.

L99 CARS weigh at least 1000lb less than a truck / suv with an L92 / L9H / L94.
L99 CARS will never tow twice their weight.

The same tuner would be wise to aim for 365-370 horses & torques in an suv using an L92 / L9H / L94.

Yes, I understand. And I agree with you. Except that high power is the correct term in this context, though high load is fine also. And I stand by my statement that 87 octane cannot be safely run in these engines if there will be any sustained high power operation, regardless of the tune. I’d like to learn otherwise, but to my knowledge, no one but GM has instrumented one of these with the necessary equipment (e.g. pressure transducers in each cylinder) to determine peak internal cylinder pressures with various fuel and spark timing settings under high power. If you want to run forged pistons, then that’s another matter.

I believe the hypereutectic aluminum alloy used in the pistons is the limiting factor. The fatigue properties of the alloy were not well understood in 2007. The casting process is prone to creating small porosities that significantly affect the fatigue strength (and by extension, the fatigue cycle life) of the alloy. Which is why I’ve said before that you might get away with running 87 for many miles, but at some point, it will be game over.

https://www.sciencedirect.com/science/article/abs/pii/S0142112307002496

 

[Marky Dissod]

Think our disagreements on how to split this or that hair detract our basically agreeing on the spirit of what we're both saying:

Any 6.2L V8 will last far longer with 91 vs 87, with or without a well-customized 'safe-for-87' tune, ESPECIALLY if that 6.2L V8 works / plays hard in a truck or suv.

I’d like to learn otherwise, but to my knowledge, no one but GM has instrumented one of these with the necessary equipment (e.g. pressure transducers in each cylinder) to determine peak internal cylinder pressures with various fuel and spark timing settings under high power.

Admittedly, even the best tuners will likely only have HPScanner on hand to peruse and analyze realtime engine sensor data while the vehicle is being driven.

 

[Marky Dissod]

The following is entirely parenthetical ...

For whatever it's worth, I've long-ago memories of tuning an iron block and heads LT1 Caprice wagon.
GM spec was 87 octane, same as what he asked for.
After a couple days of fine-tuning, I told him that I'd taken his car as far as I should on 87 octane.
He seemed well-pleased and thanked me profusely.
Several months later he called to say, he had 4 riders (his family) and a month's worth of gear in the car on a long-@$$ trip.
When he mentioned noticing occasionally disappointing responses and unusual noises from pushing the go-pedal too far past necessary, we had the following conversation (edited for brevity):

"When you and I were tuning your wagon, it was unladen, yes?"
"Yes, just you and me, no stuff; I'd cleaned most of the stuff out of it."
"Since I did not tune it with 4 other people and a month's worth of their kit weighing it down, and I can't do that now,

PLEASE USE 91 or 93 OCTANE, til I can readdress your tune, unless you're 'riding light'."

If I'd predicted his future plans to haul extra weight, I'd've held back on the tune to protect the engine.