Premium Fuel; worth the xtra cost?

[Trailer Park Casanova]

What do you think? Worth the extra money?
I read in Road & Track magazine that your engines knock sensor can effect your power up to 10%, so Premimum fuel gives you more power.
I think in my 8.1 GMC feels a bit peppier and smoother with Premium.
My boat has a knock sensor,, should I use premium in it too??
There's a 3 gas station corner in Chatsworth where Premium can usually be had for a 11 cents more per gallon at least one of them. Not a bad deal.
Any truth to the knock sensor theory??
Whadaya think??

[HOSS]

Its not a theory. An engine knock sensor will pick up detonation (whick is its reason for existence) and retard your timing. With computer controlled vehicles it depends on what the ECM is programmed for in relation to timing advance and actual compression.
To make it simple. If your vehicle`s engine has low compression chances are that the ECM will not advance the timing enough to cause damadge. After all detonation(pinging) is not good for the mechanics of a motor. Therefore you will not see any power gains by using higher octane.
If you "chip" your vehicle then you may need to run premium because of the agressive (advanced)timing.
Best thing to do is if you have a stock vehicle, then read the manual and it will tell you what octane needed for your particular motor.
Take a look at GearHeads forum under bench racers need not respond for a more "universal" form of understanding.

[Trailer Park Casanova]

My Mercury Manual, and the owners manual for the GMC both simply say; "Designed to run on 87 Octane".
Nothing else on the subject. Seems to leave it open for thought.
My Toyota shows a huge difference between 87 and 91 in terms of knock, power and MPG.

[Foolish]

Usually you will be sage running the good ole 87. However many truck engines have had problems with "pinging" in recent years cause they are trying to meet EPA regulations. One of these motors is the Dodge 5.9L Magnum...they put a huge bandaid on the situation by coming out with a ECM flash to retard timing (hence getting worse hp and worse mpg so you don't ping). Another truck that has had some problems with this is the Ford v6 truck engine...
AS Hoss pointed out 87 should be fine unless you are actually pinging and then putting 89 or 91 in your truck is really just covering up the problem cause its SUPPOSED to run on 87 octane.

[HOSS]

Air quality and fuel qualityalso play a major role in pinging. 87 from Shell as opposed to 87 from Joe`s bait shop are 2 entirely different 87`s. The Shell fuel will have less water and less contaminants therefore be of higher quality. This is why you pay more.
If your motor (whatever its in) does not ping under load with quality 87 then running 92 will not give you ANY performance gain. You will in fact get worse fuel mileage(even though minute)because of an incomplete burn. The higher the octane the harder to burn. So if your motor is tuned for 87 you are getting a complete burn. In fact you may be able to "bump" up the timing a tad(see gearhead bench racers need not reply) to get more power. If you run 92 with the same setup then you are not getting a more complete burn. Remember quality not quantity. My jeep 4.0 must run on 89. It pings with 87. I wouldn`t want to have to pay for 93. I wish it ran on 87. My Monza I ran agressive timing(36 total)for the street. I had to run 93 from Exxon. ANY other premium would ping. But I built that motor to burn as much fuel as I could "pour" into it. Fuel cost was not a concern, power was.
In your Mercury and GMC if you want to run 92 or 93 then take advantage of the money you are giving the oil companies and chip or if not ECM controlled advance timing. Then you can use the power capabilties you will be getting from running expensive fuel. But if its a daily driver I`d run water if I could. Keep the bread in my pocket.

[77charger]

I have always ran 87 in all my vehicles never a prob and could not tell the difference between 87 or 92(they are all stock and slow vehicles) :D Unless i had a 10-1 or up compression motor the 92 or race gas will have to do.
My last boat had an 11-1 motor common sense says no 87 my current boat has a bone stock 350 mag and you could not tell the difference between 87 or 92 except the price.
My couisin had a toyota truck who swore he could tell the difference in oct i borrowed it once filled it back up with 87 told him 92 he thought for sure it was 92 never told him the truth.
Hoss would 92 be better for the pcv valves though :D :D :D
[ July 06, 2003, 12:56 PM: Message edited by: 77charger ]

[HOSS]

I`ll get back to you on that one! wink

[HOSS]

77, I always wanted to ask but didn`t dare. Is that your wife in the pic? Girlfriend? Little sister? magazine pic?
How long ago was it that you sent me those fuel pump eccentrics for my 460 in my boat? 3 years?
How do you like your new boat with outdrive? Pro`s and Con`s please.

[77charger]

HOSS:
77, I always wanted to ask but didn`t dare. Is that your wife in the pic? Girlfriend? Little sister? magazine pic?
How long ago was it that you sent me those fuel pump eccentrics for my 460 in my boat? 3 years?
How do you like your new boat with outdrive? Pro`s and Con`s please. I wish but that is shania twain
been a while on those ecentrics but need to get rid of spare parts to help a boater out.
The i/o is great pros its quiet,smoother ride,more room now can have a good stereo,gas last forever,can safely take out at night
cons
Went to blythe last month shallow water worries me now,more cautious about the drive,and prop,cant idle into shallow areas(need about 4ft or chest high min)VS waist high for jet,not as fast 59-60 vs 65(jet on motor)or 71 on NOS,Acceleration not as responsive,and last i cant go to MPD anymore since he does only jets cry
My brother gets to enjoy the jet now since i rebuilt the motor last oct(2001)it has been very reliable and the pump motor combo is working really good and has been turn key all this time

[HOSS]

Way god bro. What parts ya got? Really been lookin for a pickle or Hudro. Gotta look cool ya know.

[77charger]

HOSS:
Way god bro. What parts ya got? Really been lookin for a pickle or Hudro. Gotta look cool ya know. Dont really have many parts,8 rods for 460/429 car style(square rod bolt heads)beached 1 got the dove heads,also have that part that slides on the crank before the dampner(one of those you have to buy this to get that),429 crank and a dove block(both are going to my brother if he needs them)block has a bolt broken off in it a main bearing bolt.But like i said before the local ecology auto wrecking has bbfs in there alot so hard to find parts are not a prob.Also have two newer 87 and up sbcs 4 bolt blocks but i have a use for those since my truck and current boat can use them :D Will be nice to have a complete motor on the dtand ready to drop in

[Trash]

Trailer,
Here's the skinny on premium fuel. First off, it differs whether you are talking about a marine application or an automotive application. I have personally spoken with a Merc engineer who gave me some great insight.
Automotive applications will typically run a little better with premium. Timing will be advanced more resulting in a little more power. Not always, but in many cases. Most will run on 87/89 if the manual says its okay. A few specify higher octanes because the engines run slightly higher compression and consume some of the knock safety margin. I believe vehicles like the Lincoln Navigator are in this arena. My Bronco will run on 87, but it definitely pings more than if I run 91. It's too tough for me to tell if there's any power difference in my application. Bottom line; use what your manual says or higher if you can afford it.
Marine applications (specifically Merc products) use the knock sensor in a slightly different manner. The 95 and 96 model Merc Magnums, specifically the 350 Mag/EFI MP, and 454/502 Mag/EFI MP engines, were not to be run on anything higher than 87 octane. Those who did often found a marked decrease in performance, sometimes requiring service. Merc employed logic in the ECU which looked for engine knock as do other engines. The engines were specifically designed for lower octane fuel based on the conservative assumption that this fuel was more readily available on the water than 91 octane. So why the decreased performance with higher octance fuel? There was one other logic test the ECU employed. During engine start up, the ECU would advance the timing until it would sense engine knock. If it did NOT sense engine knock, it would assume the knock sensors had failed and "pop" a code in the ECU (code 43 for inquiring minds). This would in turn retard the timing to a fixed and conservative value to protect the engine (limp home mode) until the ECU was reset by a mechanic. Thus those who used higher octane fuel would not get engine knock during the self test as the timing was advanced, thus tripping the ECU code and putting the motor in a limp home mode. It said in the manual (under fuel specifications, page 45) specifcally DO NOT use higher than 87 octane.
Later year engines had the ECUs modified to reduce the chance of popping the knock sensor self-test fail code if higher octane fuel was used. I am unaware as to the specifics though.
A lot of people in other threads here have notice excessive black soot on the transom, and most were using 91 octane. After using 87, the soot cleared up. My guess is that the ECU is looking again for knock in a nominal timing advance range assuming 87 octane. When a higher octane is in use knock may not be sensed and as a compensatory measure the mixture is richened to cover for potential knock sensor failure. This is pure speculation on my part though.
Double check your Merc manual and read the fine print and warnings. I'm not sure if they removed the wording where it says to NOT use higher than 87 octane.
That should have put everyone to sleep... wink

[HOSS]

If this is the case and the Software Engineers ( most likely Dr.`s you know PHD) did not put a limit on timing advancement into their software designs then I`d say they ain`t worht a ****! If they pulled shit like that when I worked for L3 then they`d be on the street. And I find it hard to believe that this software wasn`t thoroughly tested where as that problem would have been noticed. Those variations would be too damn close to even use unless you were in a controlled environment. And on the water it ain`t controlled. Air temperature and density alone would have a greater affect on the ECM than described above.
I`m calling bullshit on this one.
[ July 07, 2003, 06:05 PM: Message edited by: HOSS ]

[Trash]

did not put a limit on timing advancement There was a limit. It was set to sense knock with 87 octane. When knock wasn't sensed at that limit due to a higher octane fuel, it would assume a faulty knock sensor and not that the guy put better grade gas. This overly conservative assumption would protect the engine in their minds.
And I find it hard to believe that this software wasn`t thoroughly tested where as that problem would have been noticed. It was tested and was completely known. Hence the Warning in the Mercury owners manual. I'd be happy to give you page references if you'd like.
Newer models DO NOT have this issue. However, they will still run better with the lower octane fuel. In fact, I believe Hot Boat magazine even dynoed a 502 Mag/EFI MP on 87 and 91 several years ago and in fact the lower octane pulled a few more HP (about 7 if memory serves me correctly).

[HOSS]

Several years ago? Dude are you really defending this shit? Bro,,,,,,,,,just ASSUME you are an engineer. Don`t ever play like one. STOP! :cool:

[Trash]

Hoss,
I'm not sure where you are trying to go with this. Trailer Park wanted some info regarding running premium in his boat. I offered the most accurate information I had. I hope it helped him.
BTW, I am an engineer.

[HOSS]

Obviously your degree is not in electrical.

[HotHallet]

I run 87 in my truck. It's too damn expensive to run 92 in the boat and the truck.

[mtndewdrops]

Don't WASTE Your Hard earned greenbacks http://www.***boat.com/image_center/data/500/451busi002.gif
Unless your engine pings or knocks, has a high performance chip or high compression it is not necessary. You won't get better mileage or noticable power.
Your GMC runs just as smooth on 87...its a mental thing. Kind of like when you have a fresh wax job.
Want to go faster? Put down that Bimini parachute and wear sunscreen.
On the truck, get a belly pan and reduce your aerodynamic drag. A Tonneau cover helps also.

[Seadog]

Running high octane on any engine designed for regular is a waste of time and may be worse for the engine. If an engine that ran fine on 87 octane starts to ping, it probably could use a decarb or other simple treatment.