Definitive answer to effect of Octane on newer high compression engines

[JackQ]

I watched the new episode of "Engine Masters" last night where they tested a LS 6.2 liter engine with 12.5 compression ratio with various octane fuels. They even tweaked the ECM's advance curve to determine what advance produced the best power for each fuel, which in all cases was 29 degrees:

 

87 Octane 539.4 HP, Torque 498.9

91 Octane 539.6 HP, Torque 501.1

110 Octane 539.9 HP, Torque 499.1

116 Octane 541.3 HP, Torque 497.4

 

The delta of 0.2HP and 2.2 ft/lbs between 87 and 91 octane fuel is insignificant, and they determined that the different results between all the runs were insignificant, as the difference between multiple runs on the same fuel varied just as much.

 

For those who believe that you ski better on higher octane fuel, I continue to suggest that it is a placebo effect or just random. Similar on how I seem to ski better when the Orange portion of my handle bridle is on top vice the blue portion.

Fire away!

 

 

[chaloux]

Fantastic. I didn't watch the video (link?) so some of what I say here may have been covered.

 

This make sense because the ignition timing is identical. To be honest I would have expected a very slight difference in power, maybe 5-10hp, without knowing about the timing curve. But in all my time tuning cars on dynos, I've noticed a much bigger difference tuning ignition than anything else, even boost. This is usually because people turn up the boost first to feel a difference driving the car around without changing anything else, but it often nets little peak power increase - but does often give much more peak torque which makes the car feel much faster. Timing is where all the power is made. On my own personal car, I went from 27psi boost, 280whp, to 22psi boost, 365whp after jumping on the dyno to tune ignition. What a difference. Eliminating boost from the equation here, we're left with only fuel and ignition, and if ignition is the same... well, results speak for themselves.

 

Did they mention anything about knock or detonation? I'm assuming these engines have knock sensors and they didn't see anything? If they were able to keep the timing at 29 degrees over all fuel grades without knock, I see absolutely 0 reason to run higher octane in this application. Seems like they're not running into detonation issues, so the compression ratio could potentially be increased which would justify the use of higher octane fuels.

[scuppers]

Great work!

[JackQ]

They tried different advances for each fuel and were somewhat surprised that 29 degrees was optimal for all. Then did not observe any detonation on any fuel/runs. Boosted engines is a completely different scenario as cylinder pressure are much higher and detonation the enemy.

[jhughes]

Isn't the wild card here the eControls ECU tuning for these motors, in particular even by brand of marinization? I can tell you for example the 5.3 in my SN (PCM) is nowhere near the same 5.3 in the Malibu (Malibu maranization) we also use. Same GM L83 but couldn't be more different feeling and driving.

[chaloux]

@JackQ absolutely. Thanks for that bit of extra info. I haven't heard of Engine Masters, tried to google but came up with nothing. I'd like to watch that episode if it ever becomes available.

[Drago]

?

[chaloux]

@jhughes It's possible that different brands would request different tuning, but in this case, they've tuned the engine for peak performance and there is 0 difference in performance when different fuel grades are being used, indicating that in this case octane is not a contributing factor. I'm sure there are all sorts of differences between manufacturers, and realistically, this test performed on those specific marine engines would be great/ideal data to see. But on the base lump provided, we can see that octane doesn't matter. Take that for what you will, I guess.

[UWSkier]

PFI or GDI on the test engine?

[JackQ]

Engine Master is on Motor Trend Chanel (formally Velocity) season 6, episode 2. Maybe on line as well. @UWSkier, engine was Port injected, it is highly unlikely direct injection would be any different as it provide a more accurate control of the air fuel mixture.

[jerrym]

The testing was done with a high performance crate engine with no knock sensors. The engine is in a separate room so they could not hear any knocking. They purposely avoided reducing the timing to the point of knocking to avoid engine damage.

 

They noted that the testing was done under optimal air flow and cooling conditions and not necessarily what an engine will see in a vehicle.

[Horton]

@JackQ

That is great. You saw a television show. That completely overrules my communications with people at GM performance and elite skiers.

[ScottScott]

It was interesting after reading some of these threads about octane as I was in the process of purchasing a corvette, and frequenting some corvette forums, similar threads regarding octane came up.

 

A couple points made were:

 

The knock sensors detect knock and adjust timing to remove knock. But, to remove knock it must be present to detect it. How much knock is ok? Many people prefer to just avoid it in the 1st place, than to allow it to happen then have it adjusted out.

 

The debate over the additional cost of higher octane fuels were balanced by the fact that most people experienced better gas mileage with the higher octane fuels thereby offsetting the additional cost. Reduction in knock AND an actual lower cost to operate pretty much makes it a no brainer.

 

 

[jjackkrash]

In the past threads, it was pointed out that the ECM programming by the marinizer in the GDI engines was a likely culprit to significant HP derating, not the inherent nature of octane, timing and HP. I don't know this to be a fact, but that is the theory. The test above apparently removed the marinizer's ECM programming as a "control" protocol to test the effect of octane generally on HP. I'd like to see the same test run using the stock programming in the GDI 6.2L engines before declaring it "definitive" as it relates to my boat.

[jayski]

@Horton god forbid a INDEPENDENT third party did a ACTUAL test and came up with actual results which contravene your GM "expert" (whom is paid by said car company) and a group of "elite" skiers (who probably on the regular cannot afford to run premium) and at best should be taken with absolute minimal grain of salt as it is merely "seat of the pants"...A person who sits in a boat daily would notice more with the engine performance and credibility than a skier behind a boat...

 

I can definitively say I am aware of multiple sites that have had records set and personal best performances on regular grade fuel. Boat dealers that Do not run premium in their own boats, or their ski school/club boats, skis schools that have NEVER ran premium and held pro and record tourney's on regular

 

C'mon man there are so many variables in this sport that will affect scores before grade of fuel... ya gotta give it up man... :D

 

*conspiracy theory*

@Horton worked in the oil industry

Did he actually leave???

or is he a corporate propaganda expert trying to manipulate the minds of the ski masses to buy more expensive and higher margin fuel???

#russiaranianfuelspy

[jjackkrash]

Take it for what you will, but the word I hear is all the manufacturers are having longevity issues in engines in the surf boats that run the exact same engines they are putting in ski boats. Apparently, running a boat at 5k rpm/12 mph all day long loaded to the gills with lead is hard work for a gas engine (shocking I know). It would not surprise me if I learned that the marinizers were being overly cautious with the ECM programming for a number of different reasons.

[Horton]

[jjackkrash]

@jayski, they removed the marinazed ECM programing as a variable. How does that test confirm or deny that specific ECM programming is derating the engine on lower octane fuel? I am not saying it does or doesn't, just that the test was expressly not testing to prove or disprove the ECM theory floated on the forum.

 

I am in the "probably placebo" camp, but also in the "test for the right thing" if you want to prove or disprove a specific theory camp.

[Dacon62]

What my ears hear with different octanes in my 2017 6.2 truck going up a hill.

87 much detonation.

91 minimal detonation.

93 no detonation.

Manufacturer specifies 93 octane.

Even with all the sensors and electronics the timing can’t change enough to eliminate the detonation on the lower octanes.

Don’t know if the marine versions react the same way?

But they would be under load pretty much all the time except at idle.

[AdamCord]

@Dacon62 exactly. @JackQ these engines and their controls are much more complicated than that. Under perfect conditions on a dyno I'm sure you can get similar numbers with different types of gas. But we don't run our boats in those conditions. Intake air temp, oil age and viscosity, coolant temp (especially on a lake with seaweed that clogs filters) and even fuel (your 87 vs my 87 vs the 87 they used in this demo) are not all created equal.

 

These engines run a 12.5:1 compression ration. Why did GM run ratios between 8 and 9:1 for 50 years and only switch to 12.5:1 now? Were they just stupid for all that time if you clearly can run 87 in a 12.5:1 engine without issue? We know 12.5:1 is better because it is more efficient, makes more power, and burns cleaner.

 

The reason they didn't do it and the reason they require high octane in vehicles with this engine is knock:

 

 

Gm has smart controls engineers and they know not everyone will put high octane in their trucks all the time, or that people make mistakes, or even that sometimes the octane rating at the gas station is incorrect. So they design the system to retard the timing in the case of knock to keep from damaging the engine. This lets you run 87 and maybe you won't notice, especially driving to get groceries in your truck.

 

But it's a different story in a boat. We push the engines way harder than your average truck owner. We load the engine to the max coming out of the hole during the deep water start, run at high rpm and power down the lake for ~30 seconds, then drop on the ends and the engine heat soaks for a minute before we do it over again and again. This is not what these engines were ever designed for. Unless you are pulling tricks or wakeboarders you will get knock doing this with low octane fuel at some point. When that happens the ECU goes into a derate mode to protect the engine and then the power curve shifts. The Zero Off settings were dialed in for these boats using good fuel and with the engines running properly. As soon as the power curve shifts the feel of the boat shifts considerably.

 

Maybe if we could go in and adjust the gains and other variables in the ZO software we could make it feel the same running 87, but currently that's not an option. And even if it were, you're still potentially damaging your engine long term, which is why GM says not to use less than 91.

 

[DW]

The parameter I would look at is transient throttle response, not WOT power output as I interpret the way JTH laid out the issue.

 

It would be interesting to run a slalom course map on the dyno, and include different skier load profiles. That would take a lot of input data and a decent programmer.

[Horton]

@AdamCord they saw it on television. You can't argue with that.

[Than_Bogan]

@DW Yes, that. Power is not very important -- we have way more than we need!

[vtmecheng]

What possible benefit could the engine design engineers have for requiring higher than necessary octane? This would be a strange conspiracy. Just use what they recommend and have fun skiing already.

[slow]

Horton / Cord. Do some blind tests to prove your point. Otherwise your pissing in the wind again.

[KRoundy]

Is this politics?

[AdamCord]

@slow there’s no need for me to do that, people putting on elite tournaments already know this, it’s not a debate. I chime in here to help explain to people who are confused or unsure about it. If someone else wants to go through the process of a true blind test then go for it. I do believe @Horton did a test (although not blind) and skied better with the correct fuel.

[slow]

Not saying your wrong, but you really don’t know until you test it. Placeabo is a strong effect. You’re an engineer, you know that.

[Broussard]

@jayski Who is running low grade fuel for pro tournaments?

[RAWSki]

This re-hashed argument is making me long for the days of politics on Ball of Spray.

[Horton]

@RAWSki me too

[Horton]

@Broussard what fuel does kiwi run?

[Broussard]

@Horton 87 in 6.0L, 93 in direct injection 6.2L.

93 Octane was used exclusively for the MasterCraft Pro.

[Bruce_Butterfield]

@Horton "If somebody would just kill me that would be great".....I'll gladly do it, or do we need to have a contest for who gets the honor? :D

 

@AdamCord "there’s no need for me to do that, people putting on elite tournaments already know this, it’s not a debate." Sorry, but comments like that peg my BS meter. Everything to date has been hearsay and ancectodal. Maybe there is a perceptible difference in the pull with varying octane, but stating something as fact in the presence of an abundance of contrary information doesn't make it true.

 

The initial post doesn't absolutely prove anything - its just a data point. How the power varies in a ski boat is dependent on the multitude of factors already listed. Then how that affects the skier's performance is an entirely different analysis. On a Pareto analysis of the things that affect a skier's performance, octane is waaaay down the list.

 

A truly blind test, varying only octane, would be the only way to really show the difference.

 

I'm open minded and ready to be proven wrong:)

 

 

[Adam Caldwell]

Maybe this argument needs to be changed to: Octane 100% matters when you put more then 500-600lbs of line tension into the system when you come off the ball. If you don't, its possible you will never know the difference.

 

I'd venture to bet that the pure momentum of the boat traveling at 34 or 36mph is enough to overcome a sub 600lb pull off the ball.

 

[Horton]

@adamhcaldwell That's very good point. I think that the argument also needs to be explicitly focused on boats with the newest engine technology. I think some of the people in this argument miss that detail.

[Nanu_Nanu]

Hahahaha!

 

 

 

[Keith_Menard]

@AdamCord I am whole heartedly in favor of feeding the beast the gasoline it deserves, but I can't quite get behind us being harder on our engines. Yes, there is abuse that goes from full to no throttle over and over again, but you don't have the drag that an SUV has, the sudden shocks, and most boat owners warm up the engine first and an endless supply of cold water (which is both good and bad), not to mention the lack of accessories.

[Keith_Menard]

@Broussard That is one reason I loved that 6.0...good power and would burn lake water if that's all you had.

[ScottScott]

@Keith_Menard Remember that that SUV had a transmission with multiple gears to match that load with optimal gear ratio, the boat does it all in a single gear.

[jjackkrash]

@Keith_Menard, I am not 100% sure what you mean by "drag" in this context, but a boat is under a heavy friction load 100% of the time running in water; a boat does not "coast" like a car heading down the freeway and it does not have wheels that roll. A boat is more like a car driving up a steep hill 100% of the time. Marine engine hours are way harder on an engine than car engine hours under most regular use cases.

[RAWSki]

@jjackkrash have to kind of disagree in that not 100% of boat hours are under "heavy friction load". Hook a computer to the engine and I would guess 30-40% of the hours are at idle, those hours aren't too hard on these engines..... no matter the octane.

[jjackkrash]

The engine is not working hard at idle, I agree. But when it is running on a plane, it is working. Most of the time spent in the course is at 4K rpm ish or possibly more.

[slow]

Wake surfing seems much harder on an engine. Talk about heavy load. My 1999 ski Nautique gt40 has 1500 hrs no problems for skiing.

[Kenboat]

I been into fast boats, motorcycles, and cars for years. Hi compression engines do require high octanes to prevent engine damage from the fuel air mixture exploding on its own rather than the spark from the plugs. Almost as if it acts as a diesel engine. You normally hear the pinging from the engine and if left unchecked it will destroy the engine. Most of our marine engines are lower compression and have limited spark advance and do not need higher octane fuels.

Octane prevents pinging but does not really make more power on its on.

That is why the HP output in the test is very similar and the variations could just be due to changes during the test conditions.

 

So save your money and run the octane fuel recommend by the engine manufacturer

I will add the quality of the fuel could also make a big difference, does it use MTBE, ethanol, or other additives. In the north we have winter vs summer fuels that are easier to vaporize in cold weather.

I run 91 octane marine fuel for the fact that being non ethanol it is much better on the rubber and plastic parts in the boats fuel system.

 

[sgregg]

Wonder what engine/octane they were using at Okeeheelee in 2000.

 

https://www.sun-sentinel.com/news/fl-xpm-2000-09-24-0009240153-story.html

[ForrestGump]

It'd be interesting to get @Greg Banish thoughts. He's been a powertrain engineer for the big 3 for many years. He's probably dyno'd and tuned more fuel injected engines than most people in the business.

[escmanaze]

"Definitive Answer"

 

:D :D :D :D :D :D :D :D :D :D :D :D

[DW]

@Keith_Menard - Aero drag of a modern SUV is actually quite good, Cd values in the mid .3, the surface drag due to large wetted surface of the current boats has a much higher drag level than an SUV at legal speed limits. My experience watching ski boat operators is not aligned with yours, I have observed must simply idle out to the start point then go. Automotive engines also warm up much faster due to the recirculation of the coolant offering constant source of heat. Numerous posts on RPM histograms show ski boats spent up to 50% of their time at idle, and yes, pulling a skier is akin to heading uphill.