Testing the Octane theory

[OldboyII]

IMO the key point is that R&D of automotive industry uses standard fuels which pass strict quality control in their lab. They do not use any fuel from the nearest gas station ))

Whereas gas which we buy today is different from gas which we bought yesterday. Even from the same pump. Too many sources of supply and quite soft parameters tolerance. It is always slightly different gasoline.

[The_MS]

Put the 39 guys on side by side boats, each with different fuels and have them tell you which one has the high test. Done

[Horton]

@The_MS that would be ideal. In fact, I really hope somebody does that. My test is the best I can manage at the moment but is admittedly inadequate. I am just stirring the subject hoping someone will step in with a better test.

[thager]

Hmmm, "Stirring the subject?" Then are you just going to leave? How original!

[MDB1056]

$2100 over 1500 hours use, at 50 hrs a season avg that’s 30 yrs, $70 a season , $1.40 hr. Sorry but from my chair that’s not significant. Loses credibility to the cost savings argument

[jjackkrash]

Well, in fairness, for me, its about $1.25-1.50 difference between 87 and non-eth premium. Its not a deal breaker for me but not exactly trivial either. Maybe an extra $40 bucks on a full weekend of skiing with the boy and his cousins and friends.

[Horton]

since this argument should only be about the latest technology NEW boats I don't really understand how the fuel cost is significant. You spend 80 plus grand on the latest boat and you want to put the cheapest gas in it to save pennies? I mean you bought this boat because you're committed to the sport right?

[vtmecheng]

So if I can either get 90 octane non-ethanol or ethanol fuel at 91 or 93, is it better to go with the non-ethanol or higher octane?

[bishop8950]

While practicing at a Big Dawg stop, KLP came into the dock after his ride and I heard him say “you are running 87 in this boat aren’t you”? To which the answer was yes. He shook his head and said “it should be premium”. Yes, KLP is one of the most technical skiers ever and was running 39 at the time.

 

I can run 39 and am not sure I could personally tell the difference. But I bet some can. Maybe KLP had a lucky guess or maybe he knew. I am assuming it’s in the ball park of a ZO setting change. I have larger demons in my own head or behind the wheel so I haven’t gotten far enough down the list to stress about fuel. This said…

 

I agree if the boat runs better with it, especially when the cost isn’t significant in the overall scheme, and especially if it’s in a tournament, run the correct octane.

[skierjp]

@vtmecheng I think the non ethanol is more for boats that don't get used daily or weekly. I have never bought non ethanol fuel, not even for my power washer or yard tools that I only use a few times a year. Never had a problem. I know that tournaments are not putting non ethanol in my boat. My Corvette sets for weeks with no issues. If I was storing the boat or car for the winter I would probably use non ethanol. As far as octane goes. Boat and car get 93?

[AdamCord]

@Horton

 

"Jeff called Bud Pennington who until recently worked at Chevy Performance - next gen Corvette development and such. Bud’s answer was unequivocally yes. Octane would impact how fast the motor could deliver another 100 RPM."

 

This exactly. We need the motor to respond very quickly to an applied load that comes on in milliseconds. How it responds will help determine whether a skier digs in and gets overloaded or if they start accelerating early and can stay on an early line. This is why on the longer lines it doesn't matter as much. At the 38-39-41 the skier has 10 feet or less to get the swing going. If the boat responds slowly you will get overloaded, and because ZO wants to get a good time, it will have to keep accelerating as you swing into the preturn, making it more difficult to get high on the boat as it tries to run away form you.

 

I understand the skepticism. For most older boats octane doesn't really matter much if at all. For most of the line lengths people ski at it doesn't really matter a ton. But on new boats at very short rope lengths? It makes a huge difference.

[Nanu_Nanu]

This conversation is hilarious! if you think you're going to get noticable gains swapping octane levels. Ive got some snake oil I can sell you! Haha

[Zman]

@Nanu_Nanu Just curious. Are you in the 38-39-41 off category noted, skiing behind the latest boats with DI 6.0 or 6.2 engines?

I'm not, so this conversation doesn't pertain to me. For me, the first 20+ things challenging my skiing is...my skiing.

[AdamCord]

@Nanu_Nanu wait till you hear what 1/100” fin change does to your ski ?

[Nanu_Nanu]

@zman my apologies if I offend anyone this thread is just comical. If you can't notice gains swapping octane in a car you sure as heck arent going to in a boat.

 

I'm not sure completely what you're asking but I gather it's details about my boat. I run a 94' Eliminator Eagle 25' with a mildly built carbureted 454. I'm not lucky enough to have that fancy DI or timing advance or knock sensors.

 

Yeah my skiing is challenging but it's awesome

[Nanu_Nanu]

@AdamCord well...? haha

[Zman]

It's all good!

[IGski]

@Nanu_Nanu We would love some video of you skiing behind that beast of a boat!

With 93 octane please.

 

[Horton]

@Nanu_Nanu The primary focus of this website is competitive skiing. Everybody's welcome but your comments clearly outed you as not being involved in the competitive side of the sport.

 

This thread specifically is about that last .01% of boat performance for a fraction of a second for people who are mostly in the top 10% of the competitive sport. In other words, it id way the hell in the weeds.

[skiinxs]

Once you have changed to the higher octane, disconnect the battery for a couple minutes then reconnect. This will force the ECM to relearn and the higher octane should be notable if it makes a difference. I would also do a wide open run on both octanes and note rpm and mph. If that doesn't change, there was no effect (unless your boat is able to bump the rev limiter on lower octane fuel).

 

As I mentioned a long time ago in this thread I had noted a huge difference in top speed / rpm on my 6.2 as well as an octane detune in diacom a couple years ago after returning from Wichita.

 

Now for the good news if you feel that octane makes a difference. When I got my boat back to my lake after Midwest Regionals, I plugged in Diacom and there was no octane detune present and it easily hit the rev limiter. It picked up over 20 hours pulling Regionals, so the full tank of 93 octane it arrived with was long gone. Since nationals is at the same site this year, you can reasonably expect that the boat you ski behind at nationals is running 93 octane!

[JackQ]

You’re ECM does not need to relearn the map, any detonation will retard the ignition advance within 10-15m/s without any intervention. Keep in mind the higher octane fuel has no more energy than regular only allows higher cylinder pressure before detonation, other than than zero, zip, no increased energy or power.

[skiinxs]

@JackQ If you don't disconnect the battery, it could take a tank or two for the ecm to "forget" it is in low octane detune mode when it is pulling ignition advance to prevent knocking. That it the reason to disconnect the battery once better fuel is loaded. I agree that higher octane does not have more energy, it is actually is a little less. The improvement only happens if the lower grade fuel is causing an ignition retard due to detected knocking. For the 13 6.0 PCM's i owned, I never had any instance of a detune on 87 octane fuel, so any higher octane would have been a waste of money. On the four higher compression 6.2's I have owned I absolutely get a detune with anything less than 93 Octane. This shows up as lower rpm at WOT and a Diacom indication of an octane detune.

[Horton]

MasterCraft tells me that the ECM relearns the octane almost immediately at engine start.

[Horton]

OK so this is profoundly unscientific. I understand this is totally anecdotal.

 

I skied 10 sets behind my boat with 87. I was running somewhere between 3 and 5 at 38 every ride. It felt fine. Whatever. @rico drove my 10th ride with the 87.

 

For the 11th ride I went next door and skied behind @rico’s identical boat that has only ever had 91 in it. Both boats are 6.0 2021 ProStars (mine is prettier). That first ride behind @Rico’s I ran the first 38 I have run in weeks and got 2 @ 39. I believe I felt more swing and was wider.

 

Ride 12 back at my house with a tank full of 91 I did not run 38 again but do think I have more swing than when I had 87 in the boat. ( Fuel is not going to fix what I am changing on my gate)

 

• If you have an old boat, never mind.

• If you run less than 35 off never mind.

• If you have a current tech boat and are trying to run 38 or shorter I suggest you at least consider that this is real thing.

 

[dvskier]

@Horton Does Rico have a tower?

[Zman]

@Horton Changing your gate? Two hands? B)

[The_MS]

@Zman He needs to

[buoyboy1]

If you want a harder faster pull/slingshot off the ball why not simply use C3 instead of higher octane... :p

[JackQ]

@skiinxs I do not think you fully understand how the ECM works, it is in a constant loop, if it detected detonation, it reduces timing, if on the next engine revolution or within that revolution (depending on ECU) on the next cylinder to fire it looks for detonation, if observed, it again incrementally reduces the advance. It keeps doing so until no detonations is observed, then it will start to advance the timing until either detonation is observed or "full advance" is reached. Essentially the ECU will always constantly work to be just on the edge of detonation. If you do not have high enough cylinder pressure to cause detonation, does not make a difference what octane fuel you use.

[JackQ]

I have an handle that has one side orange and one blue, as it should be for a Florida Gator. Today I had the blue side up and kept missing 39, but I turned the Orange side up and ran 39 and got back in the boat. So everyone should keep the orange side up!

[liquid d]

There are so many friggin variables in skiing ; consistency is the objective for which to strive.

ropes, altitude, air temp, water temp, water conditions, size of the engine, maybe the lag of the engine gives you a millisecond and acts like a stretchier rope, or more like perfect pass that let you pull it down a bit, or stiffness in a ski, or torsional stiffness in a ski, or softer tail flex....I think you get the point.

ps: Rico swerved.

[B_S]

Shortly before I bought my current boat, SN200 with the H5 5.3DI, I was considering a 200 with low hours. Then, I heard about the new DI engines that PCM was releasing in the '16 model years. I decided to make the plunge and buy new so that I could have this tech. All of my current vehicles have DI and I appreciate the added performance that they over. Premium fuel is manufacturer recommended for all, so that's what I give them, because I believe in following manufacture recommendations and want to optimize the performance that I paid for. It's the same with my boat. Even though I'm not an elite skier, I don't want to use fuel that will limit the performance I've paid (a lot of $$) for. It's that simple.

[skiinxs]

@JackQ I do have a pretty good handle on how ECM's work. I am also aware of how the new engines with both pre-cat and post cat O2 sensors adapt fuel curves when running in closed loop, but that is not what is important here, knock sensors detecting pre-ignition knock and causing a derate which retards timng advance is the key. What I also know for sure is that when two of my boats have been in derate mode with timing retarded, on one occasion after putting a good supply of Klotz octane boost or on a different occasion running down to almost empty then adding a full tank of 93 octane I pulled a couple sets, then made wide open runs. Both times I was still down around 9 mph and around 1,000 rpm's. Both times I then plugged in Diacom and could see the octane derate and timing retard present. Both times I then disconnected the battery for a couple minutes, started back up with Diacom still plugged in and the derate and timing retard were both instantly gone. Both times I then took a wide open run down the lake and the 9 mph and 1,000 rpm's were back. On neither occasion did the ECM's immediately adjust after getting good fuel. Since I didn't program the ECM's I can't tell you how the adaptive learn is programmed, but I can certainly report on hard data of how they acted in the above situations.

[vtmecheng]

Just use what the manufacture recommends and get back to skiing. Worry more about the food you eat, your ski, and your form. Even as a lowly 15 off skier I will always use what is recommended and move on with my life.

 

On my previous question, I asked about the non-e because the Ilmor manual recommends both 91-93 octane and non-ethanol fuel. I was curious what people would say. I’m aware of the correct technical answer that ethanol is fine in newer engines that run often. If you don’t run it often enough the ethanol will pull in moisture. Once the new Mastercraft is on the lift I’ll go for recommended octane throughout the season. At the end I’ll switch to non-ethanol for a few sets to get ready for winter. Beyond that, I’m going to worry about getting that line shorter and not the gas.

[ScottScott]

@skiinxs Most of this thread is talking about pretty subtle differences that only the shortest line skiers would likely notice. 9mph is a huge difference in my book.

[Kwoody51]

@vtmecheng non ethanol is always better as ethanol blended fuel has less BTU (energy) per gallon than non ethanol fuel.

 

Non ethanol gas= 114,000 BTU/ gallon

E10 = 108,608 BTU/gal

E15 = 106,814 BTU/gal

 

Minor but this would likely impact power more than a few points of octane.

[Cnewbert]

I don’t know how applicable this is to ski boat performance and the particular engines currently used, but I am researching new trucks as our current F350 diesel dually is more truck than we need, bought when we were trailering horses from FL to PA and MD and back through the mountainous Shenandoah Valley several times a year. It’s overkill for hauling our Prostar back and forth to the lake over flat FL countryside and expensive to run and maintain. I’m looking at the F150 with the 3.5L V6 EcoBoost engine. I came across an article in Car and Driver where they tested this truck and motor with both 87 octane and 93 octane. Here’s a couple excerpts of their results:

 

“With the fuel tank filled with 93 octane gasoline, the Ford F150 turned in a 0 to 60 run in 5.3 seconds. It is quite an impressive achievement when you consider that the Ford F150 weighs nearly three tons (5,594-pounds). When the C&D crew switched over to 87 octane fuel performance dipped noticeably. The Ford F150 lost 20 horsepower and half-a-second on the track.”

 

“Here is a list of the results:

 

87 octane 0 to 60 run: 5.9-seconds

93 octane 0 to 60 run: 5.3-seconds

87 octane quarter-mile time: 14.5 seconds

93 octane quarter-mile time: 14 seconds

Speed trap findings: 4 mph difference

87 octane shows 1.9 psi dip in turbo response

So what do the findings mean? You don't have to be an engineer to see that 93 octane gasoline outperforms 87 gasoline. To show this more clearly C&D performed a real-world test that proved premium gasoline performs better. They took the vehicles used for testing to an interstate where they set the cruise control to 75 mph. Cruising at 75, the testers found that premium (93 octane) gasoline returned 17.6 mpg. When they changed the fuel to regular (87 octane), they found that the Ford F150 with the EcoBoost powerplant achieved 17 mpg, a difference of .6 mpg.”

 

Again, I have no idea what this means as applied to ski boats and slalom skiing. But in the original thread on the subject of octane, many insisted octane only affects the tendency for an engine to knock, and had no bearing on the engine’s power or performance. But the Car and Driver testers seem to arrive at a different conclusion for what that is worth.

[eleeski]

@Cnewbert Ski boat engines are not turbocharged. A turbocharged engine has vastly different operating parameters from a normally aspirated engine. High octane is critical for a turbocharged engine it's actually intriguing that the F150 engine did that well on regular. 375hp losing only 20hp (5%loss).

 

Engines are tested at "standard temperature and pressure". Lots of "standards" but typically 60F. Colder temperatures will give higher atmospheric density and a normally aspirated engine will develop more power and be more subject to knocking. Hotter temperatures will have less density and the engines will develop less power while being less prone to knocking. At Horton's test site in Bako, it's pretty hot right now, probably a bit humid with thunderstorms over the mountains and there's always a thermal low when I fly over this time of year. Plugging that into the density altitude calculator (99F, 70F dewpoint, 29.85 inches pressure) gives a density altitude of 3000 feet. Since normally aspirated engines lose about 3% of their power every thousand feet of altitude gain, Horton's boat is down close to 10% power (twice the loss in the turbocharged F150!). My old Datsun 2000 tuned for Tahoe would quit knocking by the time I got to 3000 feet so a knock sensor would be reacting quite differently on a hot Bako day than on its standard day. Lower octane fuel burns faster (and often lower energy density alcohol is added to improve octane) so regular gas could deliver more power in a rarified air situation - like what we normally experience waterskiing.

 

Whatever premium power effect that is claimed is thermodynamically lost in the background of real world conditions.

 

Will we now have to run slalom events in the early morning to take advantage of our expensive gas? At least the kids and trickers won't be sacrificed to the early morning cold!

 

Eric

[Cnewbert]

@eleeski thanks for that explanation. It’s not a simple subject, at least for the layman. So many variables!

[Dysco]

Bottom line is that Horton is convinced that lower octane fuel will prevent him from skiing his best, so he better run high test in his boat.

But then again, at his next tournament he's going to be mentally SOL if the boats are burning low octane. Better run low octane to gain the mental edge.

 

Pretty much sums it all up.

 

 

[jjackkrash]

I think there has been a lot of extrapolation about how octane and ecm's "work" and it is nice to see hard data from skiinxs. The marinizers (PCM, Ilmor, Malibu) are not bound the ECM code/programing in the cars and might have other reasons to aggressively derate the power through programming for whatever reason, perhaps to protect the engine. The word is they are having a hard time with surf boats running WFO at 11 miles an hour and keeping these engines going for the normally-expected service life, so who knows. But a 1000 rpm drop tells be something is going on that's not trivial.

[Jody_Seal]

So you went from a 50 mph boat to a 41 mph boat???

On fuel octane difference???

9mph????

Thats some funny stuff right there!!

I want to say it!! But I wont!!!

 

[ETskier]

@Cnewbert My ski partner loves his new F150 5.3 ecoboost for towing around Central FL.

[Cnewbert]

@ETskier thanks for that! We’re getting pretty serious about it. Still need to be sure it’s sufficient for our horse trailer. I know it will just fine for our Prostar.

[skierjp]

@Jody_Seal sounds to me like 50 with the Hydro Gate up and 41 with it down and that's still a stretch.

[Inboardfix]

Saturday I went to fill up my boat. As mentioned earlier I have a 6.2 DI engine. My intention was to fill up w/93 octane to see if I noticed a difference from the 87 octane I've used since owning this boat. Got to the pump and 93 was $3.99 pg and 87 was $2.89.

 

Despite what @horton says, it is about the money and as I mentioned earlier the cost/benefit analaysis of the individual boat owner. On this particular day it would have cost over $40 more to fill up my boat (plus I top off my car while there). Just couldn't bring myself to do it. Using the calculations stated earlier over a 1500 boat hours period the cost difference between 93 and 87 would be $6600.00.

 

My personal cost/benefit analysis came to the conclusion w/2 kids in college (one will be skiing for Bama this fall, check out her instagram photo on the homepage, Roll Tide!!!), a 14 year old eating me out of house and home and a wife who doesn't understand living w/i our means, I decided losing a buoy or 2 was worth the cost savings.

[Jody_Seal]

But Tim your not a 39 off skier!!! Lol!!

We are not supposed to comment because we are not 39 off skiers....

 

[Horton]

@Inboardfix I assume you're riding a three or four-year-old ski & your ropes are 2 years old or more. I completely fail to understand how you can afford a 6.2 DI boat.

[Drago]

Gotta stop the bleeding somewhere

[Jody_Seal]

@Horton look into the toad!!

 

 

I don't give pandas!