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View Full Version : 89 octane in a 496



dunaholic
06-13-2007, 09:14 AM
So I am running a stock 496 mag in my boat (I know what some are going to say, so save your comments please) and was wondering if I really need to run 91 or is 89 sufficient.

spectras only
06-13-2007, 09:20 AM
Run what mercruiser recommends for your engine in the manual . They recommend 87 for the 377 [ 6.2 ]and that's what I put in mine . Can't tell the difference when I tried higher octane . The computer is calibrated by the factory , and unless you reflash it ,you're wasting money putting higher than the recommended octane.

JB in so cal
06-13-2007, 09:23 AM
I've never run anything but 87 in my HO. No problemo.

Benjhamina
06-13-2007, 09:23 AM
I was thinking about this on the way into work this AM. I run a 496 HO and always use 91 but I am not sure I have to. I have heard if it isn't knocking your fine.

yzfrider
06-13-2007, 09:25 AM
Merc recomends 87 in the 496.

jbtrailerjim
06-13-2007, 09:25 AM
I run 87 octane in mine and have never had a problem.

RiverToysJas
06-13-2007, 09:26 AM
In nearly 5 years, I've never put anything but 87 in my 496 (except occationally if it's sat a long while). Never an issue. I've been told lowest available is fine.
RTJas :D

YeLLowBoaT
06-13-2007, 09:26 AM
if it says it needs 87, run 87. All your doing by using 89 or 91 is costing your self more money in fuel.

lalhc
06-13-2007, 09:28 AM
I run 89 in my boat

CornWater
06-13-2007, 09:30 AM
Won't make a difference on how it runs, but I run 91 just in case it sits for a while. I've already had to rebuild one motor from bad/stale gas and don't want to go throught that again.

SoCalHD
06-13-2007, 09:30 AM
I always run 87 in my 496HO, and have never had an issue.....

RiverToysJas
06-13-2007, 09:30 AM
I do run Lucas Upper Cylinder Lubricant and Fuel Injector Cleaner @ 3oz/10gallons in the boat though....and the truck.
RTJas :D

Boozer
06-13-2007, 09:30 AM
You will lose more then money by running higher then 87 octane. You will lose performance as well. When you start your boat the computer advances timing until it sees knock. If you run 89 and 91 there is a good possibility the computer will not see any knock and will cause the engine to run in limp mode.

dunaholic
06-13-2007, 09:34 AM
You will lose more then money by running higher then 87 octane. You will lose performance as well. When you start your boat the computer advances timing until it sees knock. If you run 89 and 91 there is a good possibility the computer will not see any knock and will cause the engine to run in limp mode.
Haven't had the limp mode problem, but it does seem to run rich by all of the black crap on the transom by the end of the weekend.

Phat Matt
06-13-2007, 09:46 AM
Haven't had the limp mode problem, but it does seem to run rich by all of the black crap on the transom by the end of the weekend.
Bingo.
Run 87.

ULTRA26 # 1
06-13-2007, 10:12 AM
I have an HO in my boat and only run 87. I have tried 89 and 91 and the boat runs no different.
jm

SPOCKER
06-13-2007, 10:17 AM
I run 87 in my "HO" and work her everytime im out never had a problem !:) :D

HitIt
06-13-2007, 11:01 AM
Anyone know what merc recommended for a stock 454 mag (carb'd) Gen V? Bought the boat used and cant find the original documentation. Prev owner said he always ran 91. Would rather run 87 if it is better for the motor and cheaper.

Benjhamina
06-13-2007, 11:14 AM
Anyone know what merc recommended for a stock 454 mag (carb'd) Gen V? Bought the boat used and cant find the original documentation. Prev owner said he always ran 91. Would rather run 87 if it is better for the motor and cheaper.
You can check it on the merc web-site. Looks like they recomend 87 for all the 496's naturally aspirated or EFI.

Beer-30
06-13-2007, 11:41 AM
It's low compression, has EFI and DIS. It would probably run fine on 85! 87 is all I run. Mine's an HO.

HatenWinter
06-13-2007, 11:55 AM
496 HO--- 87 octane everytime. :)

HitIt
06-13-2007, 11:56 AM
Cool, looks like I will give 87 a shot.
BTW: if anyone cares, here is the Merc Link (http://northamerica.mercurymarine.com/serviceandwarranty/mercruiserfaqs/fueloil.php)

dunaholic
06-13-2007, 12:15 PM
Great!!! Now I am going to save money, which means I can go boating more. What a bummer for me.:D

desertbird
06-13-2007, 04:04 PM
Since most docks only carry 89, I've run a lot of 89 through it. I also think that at 89, it produced the least soot on the transom. No worries, though, that's why God made HOT SAUCE!! ;)

charlyox
06-13-2007, 04:12 PM
Don't waste your money. I run 87 in my 496 H.O. and it runs betterthan 91.

Nord
06-13-2007, 04:27 PM
87 in the 502Mag here.
~NORD~

Buster
06-13-2007, 06:29 PM
87 Allways and this is why. In a stock motor(496 HO) 89 or 90 octane fuel will burn slower (lower flash point) causing each cylinder to not burn all the fuel it was delivered. This is why you get the black crud on your transom. Higher octane fuels are intended for high compresion motors with bigger cams.
Save your money for more beer ... :D

BoatPI
06-13-2007, 06:45 PM
A number of years ago I went to the Merc school at their HQ. I still recall today the instructor driving into our head to ALWAYS use the octane suggested by the factory. If it is 87, like most Mercs, then 87 it is. You will see perhaps a reduction in HP, and NEVER any gain with 89 or 91.

JB in so cal
06-13-2007, 06:46 PM
87 Allways and this is why. In a stock motor(496 HO) 89 or 90 octane fuel will burn slower (lower flash point) causing each cylinder to not burn all the fuel it was delivered. This is why you get the black crud on your transom. Higher octane fuels are intended for high compresion motors with bigger cams.
Save your money for more beer ... :D
Whatever...three years has flown by in a flash, huh?:idea:
http://www.***boat.com/image_center/data/520/2271MagicAlmost.JPG

Buster
06-13-2007, 08:01 PM
Whatever...three years has flown by in a flash, huh?:idea:
http://www.***boat.com/image_center/data/520/2271MagicAlmost.JPG
No chait !!! You going this weekend?

JB in so cal
06-13-2007, 08:11 PM
No chait !!! You going this weekend?
We'll be out. Be safe!

bob briley
06-13-2007, 08:13 PM
87 octane 496ho with a procharger 3.5psi ,no prob