Octane / PCM H5DI (5.3l)

[jjackkrash]

I was reading the owners manual on it says it will run on 87, but it also says the computer will adjust to higher octane fuel. Does anyone know whether higher octane fuel will get better performance with this engine, or whether higher octane is just tossing money away?

 

I have heard that it is best in most engines to use the octane rating it was designed for, and not higher, and that using more expensive fuel is just a waste of money. But I don't know for sure whether (or not) the computer and direct injection can take advantage of more expensive fuel.

 

Anyone know? @Jody_Seal?

[Gloersen]

higher octane would offer no advantage.

 

if compelled to purchase more expensive fuel, choose ethanol-free (probably 89 octane), especially if the boat sits for extended periods.

[B_S]

You can run on 87, because the computer will adjust to it, but you will get higher performance out of this engine running premium fuel. This is stated right in the manual. This not the same thing as putting premium in an engine which is made for 87, which is what Gloerson is talking about.

[Gloersen]

@B_S is correct in that higher octane (93) will yield higher performance (more torque, more HP). Minimum advance timing for best torque (MBT) is not limited in the H5; higher octane - more torque.

 

However, the chosen statement, "no advantage", holds true in that these engines have an ECM tune calibrated to run effectively on 87. The engines's HP though is likely rated using 93 fuel and "optimal performance" may be at 93 (as stated in the manual linked for reference, page 22) but it would be debatable if such yields any advantage. That is will the pull be better or the fuel economy?

 

Both probably negligible in terms of pull or fuel consumption/cost.

 

If short set-ups and/or high altitude (although engine knock is less likely at higher altitudes - less compression, and timing advance not as much a factor with higher octane) are issues then 93 is something to consider.

 

FWIW I run ethanol-free 91 in the H5-5.3DI promo for peace of mind but 87 E-10 in the group 196 343. For our application (running buoys) there is no notable difference in performance; after all, it's all measured by buoy count isn't it?

 

 

[jjackkrash]

Fortunately I have access to mostly ethanol-free fuel. The local guy who owns the corner gas station hates ethanol and buys ethanol-free when its available, so about 9 out of 10 tankers he has ethanol free.

 

@B_S, as far as the manual, that is what it implied but it was certainly not a model of clarity.

[B_S]

For the premium I paid for mine, I'm always going to run 93 to ensure maximum performance!

[jjackkrash]

Hehe, no kidding @B_S.

[wskier]

87 vs 91 in California 10 cents difference so the most important thing in your boat the engine. For a 30 gallon tank equals $3.00. I'll take the higher octane all day. $50,000+ for a new boat I change the oil 3 times a year and the battery once a year and impellor. 1999 snob runs like new. I ski on big lakes nothing worse than being towed in.

[skiinxs]

I would bet the 5.3 makes significantly more hp on 93, but don't know this for a fact. I can say for a fact that on the 6.2 there is a huge difference in hp between 93 and low octane fuel.

[jjackkrash]

@skiinxs, that's what I wanted to know, 93 it is.

[Gloersen]

 

[eleeski]

My Cessna 182 was approved for both 87 octane regular and 100 octane avgas. The plane (with fixed timing and a carburetor) climbed faster, got better fuel economy and ran hotter on the lower octane fuel. Performance was improved on the less expensive fuel. And I saved enough money to pay for a new engine at its overhaul time. The difference between 87 and 93 octane isn't that large but it's still a waste.

 

Waterskiing is about what the human skier does, not the boat. Boats are designed with a margin of excess performance so regardless of fuel type (or other normal variables) the boat will not be adversely affect the human performance. Use whatever gas that gives your mind an advantage.

 

Eric

[skierjp]

LOL, a video from SHELL promoting high octane fuel. I have watched a number of reports about high octane versus low octane. The general consensus is start low and if you hear knock step up to the next level of octane. You can't convince me that you would feel a <4% change in a engine with 430 hp. I have run 87 and all the way up to 94 Sunoco in my 6.2 Nautique and there is no difference! I have run 87 in my 6.2 Escalde for 70k miles and have never heard it knock. When I've tried 93 there was also no difference in power or fuel savings even when towing. These engines are smarter than us!!

I think ethanol free fuel is fine for boats that don't get used much but if you are using it on a regulat basis it may be pointless.

[skiinxs]

@skierjp The 6.2 makes so much horsepower and has so much to spare you would probably never notice the difference pulling only slalom. If you hook a strong 35mph jumper up who wants to jump in slalom mode, you would certainly be able to tell the difference in the times and with jumper feedback.

[shyskier]

There is a lot of misconception about fuel. The lower the octane the hotter the burn. The higher the octane #, the more resistance to knocking, pinging ( preignition) That is all a octane # is. Most refiners use ethanol blend to increase octane rating.

All fuels have cleaner additives, no matter the grade.

Computer controlled timing has pretty much eliminated preignition in most engines.

The only thing I use prem. for is my 2 stroke snowmobile & the new ones are now computer controlled & use knock sensors to prevent engine destruction if preignition persist.

[jjackkrash]

I just emailed PCM and will report back if I get a response on this issue.

[Gloersen]

@shyskier – put it simply accurately, octane is just a standard measure applied to gasoline that indicates its resistance to knocking (higher octane = more knock-resistant; that’s all) and various additives, cleaners are present across the spectrum for the most part. The terms “Super”, “Premium”, vs. “Regular” etc. are misleading since they connote greater energy delivery with higher octane, but that is simply not the case. Lower octane fuels are actually more volatile, that is, they ignite more easily. In fact they ignite so easily (lower octane fuels) that the ignition timing has to be retarded to prevent pre-ignition (knocking) which is harmful to the engine (big time in severe instances). In fact EtOH can be added to make fuel less volatile and thus yield a higher octane rating (but it doesn't release more energy upon ignition for a given mass).

 

Since the advent of ECMs (“engine computers”) along with an array of sensors, including the knock-sensors, lower octane fuels can be used since the sensors will relay to the ECM any pre-ignition and the timing will be retarded accordingly. A higher octane fuel is simply harder to ignite under pressure thus the timing can be advanced by the ECM (since no pre-ignition is detected) and the burn (ignition) of the fuel can take place under a more optimal phase of the piston stroke (maximum compression). Thus an engine such as the H5/H6 discussed can deliver more torque and more HP if the timing is optimized for a given octane fuel; the ECM makes use of MBT (Minimum advanced timing for Best Torque) tech. That is for the given compression ratio of the H5; 93 octane makes the most of MBT.

 

PCM will likely reply by indicating using 93 octane will maximize torque and HP (it would be good if PCM indicated how much percentage increase with 93 vs 87, - don’t hold your breath for that data) but 87 (not less) is perfectly safe and will not reduce the life expectancy of the engine (assuming no knocking).

 

It’s pretty straight forward stuff – 93 octane/EtOH free might be most suitable for your peace of mind but it’ll leave less $$$ for consuming other EtOH based fuels (which may or may not enhance performance)…

 

[bigskieridaho]

Well my Malibu manual says no less than 89 octane but 91 is recommended. So is the extra money worth it at 41 gallons???

[EricKelley]

Higher octane fuels allow engines with higher compression to operate without predetonation. As the fuel/air charge is compressed before the spark plug lights, higher compression engines can be damaged if the explosion occurs before top dead center. Lower octane fuels will combust at a lower compression than higher octane fuels. You should run the octane your manufacturer recommends, higher won't hurt but will not make more power. Just a waste of money in general. Octane rating of most fuels will go down with age, If you are going to store the boat for a long time maybe not a bad thing to put higher octane in.

[EricKelley]

The new generations of engines have knock sensors which detect "pinging" or predetonation before we can here it and adjust ignition timing to compensate for it. There is a limit to how much retarding the timing can do to help. If your manual recommends the higher octane, you are taking a chance running the lower octane and probably decreasing valvetrain life.

@bigskieridaho your engine runs right on the edge of safety with the 89. Manufacturers realize that some times you get some crappy gas. What happens if you have 89 in the tank and get some crappy 89 that is 87 or less, then you are below 89 and at risk. The hotter the temperature the more likely predetonation will occur. How confident are you in your fuel? If you fill up often and know you have good quality fuel your ok. I don't seem to trust a lot of things today.

[skiinxs]

@jjackkrash I am certain that PCM will respond that 87 is acceptable but the engine will be sluggish on the lower octane fuel. Good point by @Eric Kelley about shelf life. I seem to remember reading somewhere that gas loses around one octane point per month of storage. Stabilizer helps this, but keep the storage duration in mind when selecting octane. I can tell you for a fact and back up with Diacom files showing timing retard due to low octane that the H6 will make more power on 93 octane. If you are only pulling slalom with the 200 you really don't need the extra power from 93 octane, but keep in mind that it isn't simply changing octane for increased power, the ECM has to relearn that it now has higher octane which will take time unless you disconnect the battery to force it to re-learn.

[jjackkrash]

This is the reply from PCM:

 

"Yes 87 Octane fuel is the expected normally found octane and approved by GM

for these engines.

Will your engine like running on 93? Yes however will you see a difference

in performance? Probly not."

 

 

[jjackkrash]

I am not sure what "likes running on 93" means exactly, but I will probably run 93 because the cost difference is not all that significant to me and I want the boat running its best.

[John Brooks]

In reading the PCM manual, it mentions the following. Notice that it mentions that ethanol fuels are fine for the PCM engines but the gas tanks, fuel lines, ect are may or may not be ok. My personal preference is to use ethanol free.

 

GASOLINE CONTAINING ALCOHOL

The implementation of ethanol-based fuel is spreading

rapidly throughout the United States. As such, PCM

Engines provides the following information regarding the

use of this fuel.

This information addresses the use of ethanol fuels in

PCM ENGINES ONLY. It does not address the use of

ethanol fuels in vessel related components such as boat

gas tanks, boat fuel lines, etc.

Ethanol blended fuel rated E10 or less is acceptable

to use. Fuels rated higher than E10 SHOULD NOT

BE USED. Ethanol fuels rated higher than E10 could

potentially damage the engine and/or present an

unsafe boating condition. Damage to the engine

resulting from the use of ethanol fuel rated higher

than E10 IS NOT covered by the warranty.

[swc5150]

In my town, we can get 91 ethanol-free at pretty much every station, which is why I run with it. I can't tell the difference in performance (5.7's), but I can't bring myself to run ethanol in my (too) expensive boat.

[Jordan]

Not only is the difference going to be negligible, but speed control is going to keep the motor reacting to maintain speed such that the skier would never be able to tell which fuel was being run.

[Alberto Soares]

Here in Brazil the only gasoline available is E27, that's right, 27% ethanol. Other than getting a high fuel consumption the engines don't seem to damage from it, at least that's my own experience with thousands of hours on my boats the last 20 years (currently 200/6.0 with 1400h and Malibu 5.7 with 1000h)

[Gar]

Alberto impressive!

[DW]

@Alberto Soares : Isn't your ethanol from sugar cane? I have not studied the difference between that and the corn based ethanol used in North America.

[B_S]

@DW here is the difference between ethanol from sugar cane and ethanol from corn:

 

[slow]

Can't even believe i'm reading this thread. Ski season needs to start

[Jody_Seal]

What is being discussed also one needs to recognize the generation of engine that is digesting these fuels. The DI engine will run on about any octane fuel. It more boils down to how clean the fuel is and filtration is paramount. I run premium Chevron in my 6.2. It has up to 15% ethanol yet has all the needed additives to help keep the induction system running clean with limited deposits on valves. Utilizing ma and pop crap fuel will only cause these engines to clog up and decreases filtration efficiencies. So the rule is don't run cheap gas, run a quality fuel also change the filters more often. For lay up purposes it is best to utilize treated non ethanol fuel while boat is being stored.

[blakeyates]

Jody, does the 6.2 PCM manual recommend 93 octane? My 6.2 in my Chevy Silverado says to run 93 unless it's not available. I run 93 in my truck 80% of the time but am starting to run it consistently in my 5.3 DI Nautique.

[Jody_Seal]

@blakeyates .

any time you can run superior grade fuel the better your engine will performe . I started running chevron 91non ethanol in most every thing I own. Yet I know of boats that run under conditions that make most of us cringe on low grade crap gas and yet they run like a champ!! The key again is filtration, run a clean quality fuel and change your filters Makes life easier!!

[sunvalleylaw]

So if I am running a '98 Monsoon designed to run 89, at up to 7,000 feet, Premium 91 (it also happens to be non-ethanol) will help with knocking, but will not necessarily increase performance, correct? That is what I ran last year in my Response LX. It has some hours on it too, so I figured it couldn't hurt. Had been run at sea level previously.

[eleeski]

@sunvalleylaw The air is thinner at altitude so you are less apt to knock. So you should be able to use lower octane fuel at altitude. Since lower octane fuel burns faster and hotter and lower air pressure at altitude makes the burn in the cylinder slower and cooler you might get better performance with lower octane fuel.

 

There might be enough benefit from the no alcohol in the premium to justify its use but your boat will not see any performance increase with the high octane. Possibly worse power and fuel economy with 91.

 

High octane fuel is in itself not more powerful. Diesel has the highest energy content per gallon. High octane fuel is critical for engines designed for it (high compression engines, turbos, etc). The fuel itself has less energy content (that's why you need high compression and turbos). It is counterproductive in an engine not specifically designed for it. Or an engine at altitude.

 

When I come visit you for the eclipse this summer, I don't want any of that premium gas bringing down the performance of your boat when I'm skiing!

 

Eric

[sunvalleylaw]

@eleeski , (Eric) Glad to pull you if you come over for the big show. We should be up there camping in the vicinity of the high lakes, up near Stanley where the best viewing is. Kinda dreading all the people invading our area during that time, but, can't control the path of the eclipse. :) I will have to double check what grades are available, but it appears the mid grade is 87, non ethanol. Not sure if there is some 89 ethanol in town. My motor is rated for 89. So seems like I should stay above 87.

 

Steve

[disland]

How often do you all change gas filters? I have trouble getting those things off

[sunvalleylaw]

I pulled out the Indmar manual last night. (I realized then that this is really a PCM thread but oh well). So, the manual for my engine which is a 350 CID 5.7 L Marine Electronic FI, port injection F model, says 89 Octane is recommended in the specs. But back in the body of the manual, it says it can run on 87 or higher, and up to 10% Ethanol. So, seems a little contradictory. Also, it appears I cannot get 89 in this part of Idaho.

[Kelvin]

Yea, I always wondered why the Indmar 5.7 engines recommended 89 octane, but the PCM 5.7 engines always recommended 87 octane. Not sure what the differences were.

 

[DW]

@Jody_Seal can add some or a lot of perspective, the engine marinizers specific a grade of fuel not only for performance reasons but also have to take in to account that boats spend a lot of time sitting and time is one criteria that lowers the octane level of the fuel in your boat. I have not actually tested it, but the octane level of the fuel that just spent the last 6 or 7 months waiting to be used is not at the level it was purchased. And don't forget, they are not printing the owners manual aimed at the sharpest customer out there.

 

A naturally aspirated engine with a compression ratio of under 10:1 can easily run 87 octane fuel with ignition timing properly set. Pretty much all the engines in ski boats are less than 10:1 CR.

[skiinxs]

I believe that the 6.2 runs a higher compression ration (at 11.5:1) than the 5.3 and also the direct injection runs a lot leaner. Both of these factors would call for more octane. Old gas also lowers octane, around one point per month without stabilizer is what I have heard. What I really can't wrap my head around is how they can ping (detonate) at all since the fuel isn't even present until a millisecond before the spark plug fires due to being injected under compression. Like I said earlier though, the 6.2 absolutely make a lot more power on 93 octane than "low octane" gas. This is due to a significant amount of timing retard once the ECM picked up on pinging. What I don't know is how low the octane was.

[DW]

@skiinxs : Correct on 6.2 & 5.3 CR being in the 11's, I should have noted 'older' SBC's, but the 5.3 can run on regular fuel and for automotive E85. Just to go way off topic, have you seen where F1 engines are attempting to use oil burn as a performance boost due to fuel limitations.

[eleeski]

@disland Change what?

 

Seriously, if you lube the rubber seal with silicone grease, it is much easier to replace the filter (assuming it's a spin on cartridge style water separating filter). I change them regularly before they corrode and leak.

 

My Mastercraft has the filter in the tank. I change it when the fuel pump fails. Never seen one particularly dirty.

 

The UCLA old boat has a tiny inline filter which plugs up all the time. They need to replace it with the spin on cartridge style (with silicone grease on the rubber seal). The change process seems to get gunk into the fuel pump screen. Carb cleaner shot up into the screen with the straw deals with that.

 

Boat maintenance advice from me is worse than getting advice from the Internet. Oh wait, this is both.

 

@DW Lots of energy content in that oil even if the octane rating is low. But only VW uses that trick (sorry, we just had to give up the Jetta TDI so I'm a little bitter).

 

Eric

[thager]

@eleeski Me too. Just going to run my TDI until it dies! They all cheat. Funny how everyones speedo runs a few mph slower than the GPS says isn't it. Would that increase mpg? Doh!