89 octane vs 87 octane

[General Lee I]

I currently use 89 octane in my 1991 4.3 OMC Cobra, is there an advantage of using 89 octane vs 87 octane, does anyone know what is recommended for this engine?
Thanks

 

[ziggy]

Re: 89 octane vs 87 octane

imho, i think octane is a detonation inhibitor.
as for what's right for your engine. i don't know. my speculation would be it just want's regular fuel being that unleaded reg. was most common in '91. imho. the best place to find out exactly what it wants is to look in the oem service manual. it'll tell you what omc says is the proper fuel to use.

if that 89 octane fuel your looking at is corn fuel. i'd avoid that if possible. a '91 i doubt was set up to run alcohol, which attracts water and can degrade some rubber parts..

 

[HT32BSX115]

Re: 89 octane vs 87 octane

Most marine manufacturers now rate their engines to operate on 87 octane regular unleaded gasoline AND allow up to 10% ethanol.

In previous years OMC indicated an ignition timing setting for regular and an advanced setting for using higher octane gas.

You need to reference the OEM (NOT Seloc/Clymer) service manual for your engine to get the correct ignition timing settings for using regular.

If you run regular in an engine that has been timed to use premium, you could have a detonation event with bad results.

Most all engines have been timed to run on regular, but I would check the timing to be certain.

You probably won't notice much difference if you time it for premium and run it on premium.

Check the timing, time it according to the manual for regular gas and go boating....Premium and Mid grade is NOT always available at most marinas....


If you time it for REGULAR and then run it on premium, you WILL NOT notice any difference........ and it will NOT make any difference (except to suck more money out of your wallet)


Regards,


Rick

 

[Brewman61]

Re: 89 octane vs 87 octane

It's funny how marketing can impact us on this stuff. The place I fill up my cars offers regular (87 octane), Mid grade (89) and Premium (92). They charge the same amount per gallon for the regualr and mid grade- which if I understand is simply a blend of the regular and premium. Anyway, I usually put the 89 stuff in my cars. i don't need it, the car runs fine on regular, and I notice no difference vs using regular. But I have to put in the "better" stuff because it's the same price.
My marina only sells premium non ethanol, so that's what goes in the boat- boat runs just fine on regular. Runs just fine on 10% ethanol, but it's a real PITA to fill up a 25 gallon take hauling in cans.

 

[HT32BSX115]

Re: 89 octane vs 87 octane

My marina only sells premium non ethanol, so that's what goes in the boat- boat runs just fine on regular. Runs just fine on 10% ethanol, but it's a real PITA to fill up a 25 gallon take hauling in cans.

The lake nearby me doesn't have a "Marina" so I can't buy gas there.

If it did, the gasoline would probably be a dollar or 2 higher than at the local gas station (because it's always higher "at the lake")

I always store the boat inside with 1/2--1/4 tank so I can fill it up when we go to the lake.

I do this year after year (and I've never used STABIL or other "fuel stabilizers")

[Nothing like another testimonial huh?!!]


I have always bought the lowest price gas in town (usually at the ARCO AM/PM)
Western Wa gas stations only sell gasoline with up to 10% ethanol except certain stations that I haven't bothered to go looking for)

http://pure-gas.org/index.jsp?stateprov=WA

The closest station to me has 92 OCT ethanol free gas but I haven't verified it. (don't believe the person sitting behind counter....They NEVER know what they're talking about..............verify by doing a simple test)

imho, i think octane is a detonation inhibitor.

Essentially true. Octane number is a dimensionless number that indicates a gasoline's knock resistance. Higher "Octane" = more resistance to "ping" Wikipedia has a great description.... but they're sometimes not accurate. API backs up what they say... http://www.api.org/aboutoilgas/gasoline/gasoline-octane.cfm



Cheers,


Rick

 

[Rellik546]

Re: 89 octane vs 87 octane

i just had this convo with my brother who is a chemical engineer. he explained to me that higher octanes are for high compression motors, which is why race cars use high octanes. gas is tested with these special engines and run until they ping (detonation). i told him i was using 93 octane in my mercruiser 3.0l he said i was merely wasting money. he explained that if i was having a detonation issue and using 93 octane seems to "solve the problem" that there is in fact a problem with the engine, whatever it may be. it is actually more cost effective to fix the problem then pay up to 30 cents more a gallon for high test(premium fuel) which over time adds up, and doesnt actually correct the engine problem, which could progressively get worse. higher octane doesnt create more power in a motor, it merely has a higher detonation rating, which is designed for higher compression motors. if you used 87 in a high compression motor, it would prematurely detonate before the properly timed spark ignited. any 9-1 compression motor should use 87 octane as anything above that is a merely a waste of money IMO

i thought this was interesting because i was always under the impression that higher grade octanes, would give you more power/performance.

 

[HT32BSX115]

Re: 89 octane vs 87 octane

i told him i was using 93 octane in my mercruiser 3.0l he said i was merely wasting money.

Your brother is absolutely right. If you're using 93 octane in ANY engine that requires 87 octane, you're wasting money.

i thought this was interesting because i was always under the impression that higher grade octanes, would give you more power/performance.

Common misconception. It's due to "Marketing".

Any engine will detonate on any fuel if the ignition timing is advanced too far. Also, if an engine is "carboned" up it can experience pre-ignition (similar to detonation) if a glowing particle of carbon ignites the fuel mixture prior to the spark-plug.

No amount of Octane will prevent this.....

All gasoline (regardless of Octane) has approximately the same energy content (BTU/lb Cal/kg etc)

 

[Brewman61]

Re: 89 octane vs 87 octane

A decade or two back, BP (which was AMOCO at the time) said flat out that their "Gold" gas (Premium) provided more power, better gas mileage, and a few other claims. They were ordered by the powers that be to prove any of it or to stop making the claims.
Guess which one happened? They stopped the claims.

 

[HT32BSX115]

Re: 89 octane vs 87 octane

A decade or two back, BP (which was AMOCO at the time) said flat out that their "Gold" gas (Premium) provided more power, better gas mileage, and a few other claims. They were ordered by the powers that be to prove any of it or to stop making the claims.
Guess which one happened? They stopped the claims.

Yeah.....Look how many unsuspecting "souls" suckered into buying Slick-50 when the FTC finally sued them for false claims!

This has been going on for years!

Caveat Emptor


Rick

 

[JimS123]

Re: 89 octane vs 87 octane

The owners manual for my 1984 Mercruiser says 88 minimum octane and unleaded gas. I've always used 89, and that's all that is available on the water anyway.

Reading the link provided above, they now recommend 87 octane with no alcohol. I can understand their reluctance for specifying e10, but why have they reduced the octane requirement?

95% of the time I fill up on the highway, and have been using e10 (whether we knew it or not) for many years.

 

[General Lee I]

Re: 89 octane vs 87 octane

Wow, Thanks for all of the replys.
I've learned ALOT from this thread, I never knew exactly what octane was or did.
Thanks everybody, this thread will save me some money

 

[jamerson62]

Re: 89 octane vs 87 octane

Right below the gas cap on my boat, it simply states that the boat was tested and tuned for 88 octane gas. So I assume that I can use either or, and I simply prefer the 89 octane. Just seems to run just a little smoother with a better gas. I also use a fuel/carb cleaner every fifth fill up.

 

[Silvertip]

Re: 89 octane vs 87 octane

Right below the gas cap on my boat, it simply states that the boat was tested and tuned for 88 octane gas. So I assume that I can use either or, and I simply prefer the 89 octane. Just seems to run just a little smoother with a better gas. I also use a fuel/carb cleaner every fifth fill up.

It isn't "better gas" -- it is higher octane. Higher octane does not add power. It decreases detonation/pre-ignition. Only if the ignition system has a knock sensor which detects detonation and can therefore control spark advance, would adding higher octane fuel be advantageous.

 

[jamerson62]

Re: 89 octane vs 87 octane

It isn't "better gas" -- it is higher octane. Higher octane does not add power. It decreases detonation/pre-ignition. Only if the ignition system has a knock sensor which detects detonation and can therefore control spark advance, would adding higher octane fuel be advantageous.

Well I guess that would also leave to question that if it does all of those, and it burns hotter allowing for less un-burnt carbon build ups. Then overall all I would say it is a better gas then 87, it just might not be of any better quality. Of course this all depends on where you buy your gas to begin with, and what company was in charge of refining the crude to gas.

 

[Silvertip]

Re: 89 octane vs 87 octane

Well I guess that would also leave to question that if it does all of those, and it burns hotter allowing for less un-burnt carbon build ups. Then overall all I would say it is a better gas then 87, it just might not be of any better quality. Of course this all depends on where you buy your gas to begin with, and what company was in charge of refining the crude to gas.

It doesn't burn hotter. It has additives to prevent detonation. If anything, it ADDS to deposit build-up -- not decreasing it. Nearly every car on the planet these days has a knock sensor, crank position sensor, tempt sensor and intake air temp and air mass sensor to allow the ignition system to advance or retard timing as required to keep just below the point where detonation occurs. 10:1 compression ratios are therefore possible today whereas previously 8.5:1 was about the limit. Anything higher than that REQUIRED high octane fuel. If boats had all of those components then you could run 100 octane av-gas and experience a bit more power.

 

[seaboo]

Re: 89 octane vs 87 octane

From the OMC manual (that covers your and my boat):

"The minimum octane rating of fuel being used for your engine must be at least 86 AKI (outside the US, 90
RON), on early models and 89 AKI (93 RON) on all others, but some engines may require higher octane ratings. OMC actually recommends the use of 89 AKI (93 RON) fuel as the ideal-in fact, anything less than this on many 4.3L, 5.OGL and 5.7L engines will require a change to the ignition timing. Fuel should be selected for the brand and octane that performs best with your engine. Check your owner's manual if in doubt."

I use 93 in my boat (only because it seems to start and idle better using it). I have run 87 in it and havent had a spark knock so I am not afraid or concerned if I use it. If the boat runs good, doesn't spark knok using lower grade then why waste money on a higher grade?

*** correction...The above infomation is from a Clymers or Solec manual, NOT OMC (however it does referance a quote from OMC)

 

[TomB985]

Re: 89 octane vs 87 octane

This is a great discussion, and the vast majority of info here is completely correct. Some of your newest automotive engines will advance timing until it detects a knock, and therefore rides the hairy edge of timing. Ford actually rates my car as 10 HP higher on 91 octane gas because of this. So the principle that higher octane has no more power is only partially true. I believe the power increase to be caused by a more efficient use of the energy through more advanced timing.

But if the boat engine isn't setup to run higher octane there is no benefit. I run regular old 87 in my two other cars even when the 89 is at the same price.