Does Octane ratings affect VE tables?

[Woods]

Filling up with gas today, this question popped into my head. Would using different Octane rated gas affect VE tables? I just am curious.

Thanks

[RobertISaar]

octane alone has no effect on VE. VE is a measurement of how efficiently the engine is moving air in and out of the cylinders, thus changing octane levels won't change the quantity of air.

however, HOW the fuel achieved its octane rating, that can bring up interesting results. E0 87 and E10 87 will require different fueling, as would E0 89 vs E10 89. but, this wouldn't be accounted for in the VE tables, rather via the stoich AFR value(and PE/open loop values as well).

[EagleMark]

Did that E15 ever come to market?

[RobertISaar]

as far as i can tell, very limited release yet. i don't know if it is going to gradually roll out, or just instantly get pushed into a lot of stations....

assuming some of the original proposals are still in effect, it will actually be illegal to dispense it into a 2001 or older vehicle and the pump will be both marked and have some kind of noticable change in the handle compared to traditional designs.

[buddrow]

E85 has been available in Oklahoma at several locations for a few years now.

[EagleMark]

as far as i can tell, very limited release yet. i don't know if it is going to gradually roll out, or just instantly get pushed into a lot of stations....

assuming some of the original proposals are still in effect, it will actually be illegal to dispense it into a 2001 or older vehicle and the pump will be both marked and have some kind of noticable change in the handle compared to traditional designs.

That will help avoid a lot of damaged motors...

[Woods]

That will help avoid a lot of damaged motors...

Not being in the know, what, or how, would cause engine damage?

[beestoys]

Not being in the know, what, or how, would cause engine damage?

Most of the older designs were not fitted with components that can handle the alcohol. Some of the rubber will break down (Orings). It is also corrosive by nature and can actaully etch the metals in the system. Hence the reason that you have to be careful about using it.

[mdj]

Could octane rating allow more timing with out picking up a knock and this in turn change readings at your blm.

[brian617]

Being that VE is Volumetric Efficiency simply a representative of how the engine moves air. Wouldn't the factors in how the fuel burns ie compression ratio, compression chamber shape, cam specs etc demanding a certain fuel for the most efficient burn/combustion rate, be affected with the wrong fuel causing inaccurate VE tables, then switched to the correct fuel?

Meaning if tuning was done on wrong fuel, then you introduce the correct fuel that it could throw a wrench in your VE table? Obviously not a huge change, but a change none the less.

Or am I hypothetically digging too deep

[steveo]

Could octane rating allow more timing with out picking up a knock and this in turn change readings at your blm.

i doubt a couple degrees of knock retard (which is all you're going to get from an octane difference) is going to make a difference either way

you reach a point pretty quick obsessing about these minor things where the difference is well under 1% so you couldn't calibrate for it reliably anyway

but, that said, i had a timing table that was severly out in a few areas, and adding 8-10 degrees of timing to that area definitely tickled the wideband a bit. i'm talking 0.2-0.3 afr in open loop. maybe a few points of blm. nothing severe.

o2s seem to respond to heat to a degree too, and without enough timing that o2 is definitely going to get way hotter, and i've also heard the exhaust reaction with higher octane and race gas can be more intense, since it's burning so much more slowly, the reaction in the exhaust from unburned fuel due to insufficient timing can continue for longer

[RobertISaar]

if 10* = .3 AFR, that is a lot of timing for a pretty small change in fueling, it's nothing i wouldn't mind the O2 sensor taking care of. 14.4 or 15.0 without O2 correction is not a big deal at all.

going from 87 to 93(for example), i don't see any more than 4 or 5* at most being able to be added without detonation, and that assumes those couple of degrees are helping improve output at all.

[steveo]

yeah exactly; and i can't even roughly state 10 degrees = 0.3 AFR, just because my engine did it doesn't mean someone else's will... it's just worthy of note, especially if your timing map is way out to lunch, it should be fixed before doing any fine tuning of fueling