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Gas Octane Rating
https://www.smwebhead.com/phpBB3/viewtopic.php?f=11&t=355		 Page 1 of 1
Author:  AlexJ [ Fri Aug 18, 2006 9:02 pm ]
Post subject:  Gas Octane Rating
What is the general thinking of octane rating for the fuel we use? 87 to 93 octane unleaded gas ???
Author:  bugsdoc1 [ Fri Aug 18, 2006 11:26 pm ]
Post subject:  Octane?????
I will use 89. :lol:
Author:  jka [ Sat Aug 19, 2006 9:09 am ]
Post subject: 
I use regular...87. runs great.
Author:  Midlife Crisis [ Sat Aug 19, 2006 1:37 pm ]
Post subject: 
Volvo calls for 87 so thats what I use.
Author:  AlexJ [ Sat Aug 19, 2006 7:21 pm ]
Post subject: 
My volvo manual for the 5.0 GI calls for 93 octane. Would it be a problem to go with 87 octane?
Author:  230 Mike [ Sun Aug 20, 2006 1:25 am ]
Post subject: 
My VP manual specifies 87. Other than the one time I had to get marina gas and they only had 89, I've used nothing but 87 and had no problems. I also could tell no difference between the 87 and 89 in terms of performance.

It's entirely possible that the ECM programming has changed in the last couple of years, and that a higher octane is needed in boats built prior to that.

At current prices you'd think I was putting Unobtainium in it.
Author:  ShanMan14 [ Sun Aug 20, 2006 10:12 am ]
Post subject: 
Salesman said 89, VP manual states 87.

I've put in 87 for all 15+ hours thus far and it seems to run just fine.
Author:  AlexJ [ Sun Aug 20, 2006 12:55 pm ]
Post subject: 
It looks like the newer boats take 87 octane. What about boats older than 2000, (except for the one reply, 1995)??
Author:  teker [ Sun Aug 20, 2006 8:58 pm ]
Post subject: 
VP says use 89 so I always use it. Most sources say its a waste to use any higher octane than manual calls for.
Author:  230 Mike [ Mon Aug 21, 2006 1:59 am ]
Post subject: 
ShanMan made a good point also. Boats all needed 89 for so long, you'll still hear many sales people and others who have anything to do with boats (mechanics, marina fuel docks, etc.) just assume everyone uses 89. Around here it seems most fuel docks still don't have anything but 89. One more reason for me to fill up off the water. Know what your manual says, and follow it as a minimum; if you can only get higher octane occasionally, it shouldn't hurt anything except your wallet.
Author:  joet [ Mon Aug 21, 2006 8:26 am ]
Post subject: 
My 1998 Sundowner(VP 5.7DP) calls for 89, I have put some 87 in this year with no difference in proformance noted.
Author:  jvalich [ Mon Aug 21, 2006 8:51 am ]
Post subject: 
If we are going to use the majority of the fuel (long trip) I'll fill it up with 87. If it's a time where we are using the boat for short dy trips over a 2 month period than I fill it up woth 89. Reasoning...as it sits and ages it looses a bit of octane....so the 89 will perform a touch better than the 87 a month down the road.
Author:  Technologic80 [ Tue Aug 22, 2006 6:16 pm ]
Post subject: 
teker wrote:
VP says use 89 so I always use it. Most sources say its a waste to use any higher octane than manual calls for.


Ditto. I filled up with 87 octane once and the boat would diesel (run-on). And for 1999 5.7 GS models (CARBED), its what VP recommends.
Author:  willidg [ Mon Apr 23, 2007 3:52 pm ]
Post subject: 
From what I remember the octane rating is only for determining when the fuel will detonate under compression. So 87 will detonate under much less compression then 89 or 93. If your fuel detonates before ignition you will get a knock because it will be on the up stroke of the piston. So, on a high performance engine with a higher compression ratio you would have to run a higher octane gas. If your running 87 now and you hear no knock then you gain nothing from running 89.

Unless it is sitting for a period of time, I don’t recall how that affects it.
Author:  Jim_R [ Mon Apr 23, 2007 6:26 pm ]
Post subject: 
willidg wrote:
From what I remember the octane rating is only for determining when the fuel will detonate under compression. So 87 will detonate under much less compression then 89 or 93. If your fuel detonates before ignition you will get a knock because it will be on the up stroke of the piston. So, on a high performance engine with a higher compression ratio you would have to run a higher octane gas. If your running 87 now and you hear no knock then you gain nothing from running 89.

Unless it is sitting for a period of time, I don’t recall how that affects it.


X2.

Only time I've heard of a manufacturer calling for use of a different fuel from recommended, is when putting a much greater stress on the engine. To be specific, Honda recommends 87 for my '03 Pilot, except when towing near capacity, and then recommends 93 to avoid engine pinging.

I'd speculate that the aging of fuel does not have a linear relationship with the break down of octane. I just use Stabil or equivalent when storing fuel.
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