Why 93 Octane in a GDI engine if it isn’t called for?

[TiGeo]

Ethanol content is an important consideration here. GDI engines effectively get a large octane boost with ethanol. Around here, the choice is between 87 E10 and 91 E0, and there is very little difference in knock resistance between them on my TGDI engine.

I've made custom tunes for each fuel type, and ignition timing is pretty much the same through most of the rpm/load range, the biggest difference being 2 degrees of timing retard required above 5k rpm with the 87 E10. On the stock tune, there was quite a bit of knock on the recommended 91 E0, and virtually no knock on 92 E10.

Here you go...let the data speak! Knock retard on my tuned Sportwagen with progressive adding of E....

 

[Overfill]

Here you go...let the data speak! Knock retard on my tuned Sportwagen with progressive adding of E....

View attachment 205814

Is that 93 E10 gas blended with E85? Or are all three examples at 93 octane?

 

[TiGeo]

Is that 93 E10 gas blended with E85? Or are all three examples at 93 octane?

All 93 E10 with E85 added.

 

[wpod]

How many LSPI failures have you seen, or even just read about? There’s probably 1,500,000 posts worrying about LSPI for every engine that’s failed because of it.

We read articles. and the oil additive formulations have changed because of LSPI Truth or bologna who knows other than people in the industry.

 

[kschachn]

The root is LSPI. The use of 93 helps to prevent this, or at least some automakers. I say get rid of DI Turbos and LSPI would not be a thing, kind of like 20 years ago.

Where have you seen anything that shows a correlation between gasoline octane rating and LSPI? Every paper and study I've seen shows the opposite, that they are not connected.

LSPI is connected first to engine design and operation, then may be mitigated by the oil.

 

[wemay]

Where have you seen anything that shows a correlation between gasoline octane rating and LSPI? Every paper and study I've seen shows the opposite, that they are not connected.

LSPI is connected first to engine design and operation, then may be mitigated by the oil.

https://www.sae.org/publications/technical-papers/content/2021-01-0487/

 

[kschachn]

https://www.sae.org/publications/technical-papers/content/2021-01-0487/

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Yes I’ve seen that. It’s much more about how the rating is achieved, not about the number itself. There are multiple ways to raise the octane rating of fuel and EtOH is one way.

 

[wemay]

But it does say there is a correlation between octane and LSPI.

 

[chris719]

How many LSPI failures have you seen, or even just read about? There’s probably 1,500,000 posts worrying about LSPI for every engine that’s failed because of it.

Old post I know, but LSPI was bad enough to get like 300 journal articles published on it and every major automaker to investigate it along with oil and additive companies. I don’t think anyone would waste that time for a non-issue. LSPI could perhaps be hard to differentiate from other detonation failure modes for some. Since SN+ and SP took over quickly in the API/ILSAC oils who knows how many engines have been saved.

 

[chris719]

But it does say there is a correlation between octane and LSPI.

There are a handful of papers that say there is a correlation and a handful that say there’s none.

 

[burbguy82]

Where have you seen anything that shows a correlation between gasoline octane rating and LSPI? Every paper and study I've seen shows the opposite, that they are not connected.

LSPI is connected first to engine design and operation, then may be mitigated by the oil.

You seem to like to argue based on "data". We can argue back and forth on "data", by various sources. Eggs are bad for you says the New England Journal of Health, eggs are good for you says your nutritionist. Cherrios are good for you heart, says the AHA............and so on.

I have read in the similarites between LSPI, and good ole fashion pre ignition. In effect, not cause. I will further argue that if YOU dont know, and have read in no correlation, that does not mean that there is none.

Lets agree on somethings:

-Pre-ignition can occur when the condition inside the cylinder are such that material (in the case of published LSPI) or fuel can ignite prior to prescribed to mechanical or electronic timing

-"High" octane fuel is harder to ignite than "low" and has been used to prevent pre-ignition in high performance engines

-"low speed" component of LSPI is indicating a condition were "PI" can happen. In this case, low engine rpm, high load.

-high load=more fuel, more air

-newer TGDI engines are "high performance" as standards go

which of these do you disagree with?

 

[TiGeo]

LSPI is in my view related to overly eco-focused auto trans shift mapping. Very low rpm lugging in small fast/low-RPM spooling turbos.

 

[SubieRubyRoo]

Old post I know, but LSPI was bad enough to get like 300 journal articles published on it and every major automaker to investigate it along with oil and additive companies. I don’t think anyone would waste that time for a non-issue. LSPI could perhaps be hard to differentiate from other detonation failure modes for some. Since SN+ and SP took over quickly in the API/ILSAC oils who knows how many engines have been saved.

But again, you’re going off of articles, no personal knowledge. You’d think if it was ever as prevalent as we’re lead to believe, with such a large and diverse membership as BITOG, there would certainly be at least one member who had suffered its fate or seen an engine destroyed by it??

Maybe I’m being too critical in thinking that if there’s no objective evidence that it isn’t a real issue, but… just because somebody writes about something doesn’t make it real, or probable. I find it hard to believe that LSPI was ever the threat it was claimed to be when the members of this board have had their hands in literally millions of engines, and there isn’t one who experienced LSPI and engine failure firsthand. But that’s just me.

 

[SubieRubyRoo]

LSPI is in my view related to overly eco-foxused auto trans shift mapping. Very low rpm lugging in small fast/low-RPM spooling turbos.

And see, if I was guessing, it would be manuals and not autos, because if you prod an auto enough to build significant boost, it will downshift. The person who lugs a manual with near-full throttle in 4th gear at 15mph would seem to be an ideal candidate if the horror stories are real.

 

[TiGeo]

And see, if I was guessing, it would be manuals and not autos, because if you prod an auto enough to build significant boost, it will downshift. The person who lugs a manual with near-full throttle in 4th gear at 15mph would seem to be an ideal candidate if the horror stories are real.

Autos now hold that lugged gear well beyond any autos in the past.

 

[kschachn]

You seem to like to argue based on "data". We can argue back and forth on "data", by various sources. Eggs are bad for you says the New England Journal of Health, eggs are good for you says your nutritionist. Cherrios are good for you heart, says the AHA............and so on.

I have read in the similarites between LSPI, and good ole fashion pre ignition. In effect, not cause. I will further argue that if YOU dont know, and have read in no correlation, that does not mean that there is none.

Lets agree on somethings:

-Pre-ignition can occur when the condition inside the cylinder are such that material (in the case of published LSPI) or fuel can ignite prior to prescribed to mechanical or electronic timing

-"High" octane fuel is harder to ignite than "low" and has been used to prevent pre-ignition in high performance engines

-"low speed" component of LSPI is indicating a condition were "PI" can happen. In this case, low engine rpm, high load.

-high load=more fuel, more air

-newer TGDI engines are "high performance" as standards go

which of these do you disagree with?

You just seem to like to argue. There was nothing in my statement that was argumentative, don't be so easily offended. We aren't going back and forth about anything, you were the one making the unsubstantiated claim.

If you have read similarities can you link up some of those things?

Which part do I disagree with? That pre-ignition knocking is related to LSPI. Higher octane fuel is not harder to ignite, that is another misconception. They ignite the same. It's the resistance to self-ignition that's different.

Sorry I don't understand the part about eggs.

 

[kschachn]

There are a handful of papers that say there is a correlation and a handful that say there’s none.

Not really. There is only that one that I've ever seen and it isn't really about the octane rating, it is about volatility and composition. Every other paper I've seen shows no correlation.

 

[kschachn]

But it does say there is a correlation between octane and LSPI.

Yes but in a tangential way. It would be good to see the entire article but from what I can see is that it is volatility and other aspects of fuel related to how the octane rating is achieved. Not in and of itself related to the resistance to pre-ignition leading to typical knock.

I think that is a poorly written abstract and might have more to do with EtOH than anything else.

 

[burbguy82]

You just seem to like to argue. There was nothing in my statement that was argumentative, don't be so easily offended.

I am not. You replied to my statementy But arguing a point and arguing the "facts" is what I am talking about. It seems like anyone on here who makes ANY statement, has to have some data or peer review to substantiate it, and it must be approved by you in order to be correct. I could make the statement "Amsoil SS is the best" and have endless literature on why and how. Would the statement be correct? No, not really, but there sure would be a bunch of literature to back it up.

We aren't going back and forth about anything

I am sure we will.

unsubstantiated claim.

You were given an article by another poster on the subject, of course you reject the article as fact, and so in lies the back and forth. You have your opinion.

If you have read similarities can you link up some of those things?

see above

Higher octane fuel is not harder to ignite, that is another misconception. They ignite the same. It's the resistance to self-ignition that's different.

But it "resists" self ignition? Really? Cutting hairs. Yes it is the resistance to ignition. You just proved my point.

Sorry I don't understand the part about eggs.

My point of that was, an acknowledged source of information, like dietary information, is wrong, and therefore any source can be wrong.


So from my previous statement, which of the points I made do you agree with?

 

[burbguy82]

LSPI was bad enough to get like 300 journal articles published on it and every major automaker to investigate it along with oil and additive companies. I don’t think anyone would waste that time for a non-issue.

That wont be enough for some on here. Those 300+ articles and the investigation, are just conjecture. They did it for a non issue, that does not exist. Conspiracy! To make us buy EV's haha