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View Full Version : MCX Engine - 87 vs 89 Octane


BuoyChaser
07-18-2006, 11:52 AM
okay, sure this has been discussed before but couldn't find a post that just focused on this issue...

got my 2005 197 with MCX 350/350 which calls for 89 octane fuel...i've got a bunch of buddies that swear the 87 runs fine, that the 89 requirement is just for california emissions...

any thoughts on this, certainly a big difference in price here in New England...for 87 our price here in New Hampshire is $2.95 but for 89 it is $3.05...

so for every 10gals looking at $1 extra for 89...

erkoehler
07-18-2006, 12:06 PM
We ALWAYS run 89 in the MCX....

BuoyChaser
07-18-2006, 12:07 PM
We ALWAYS run 89 in the MCX....
my problem is, sometimes get ski buddies who bring 87 octane claiming it is 89...but they run 87 in their boat?!?

erkoehler
07-18-2006, 12:11 PM
If your using it the same day, it isn't as crucial, but MC does recommend 89 octane in the MCX engine.

east tx skier
07-18-2006, 12:20 PM
If your using it the same day, it isn't as crucial, but MC does recommend 89 octane in the MCX engine.

I believe that's the reason. Engine Nut once posted here that it has to do with assuring that you get at least 87 octane in the engine. So if you know it hasn't been sitting at the station for too long and you plan to burn it all up in a week or so, then it'll probably be alright. As he said (not a direct quote), 87 is fine, 85 is not. This may be more applicable to my carb'd motor where it cannot retard timing. Plus, my motor is low compression at 8.5:1.

phecksel
07-18-2006, 12:22 PM
I can tell the difference in pull between 87 & 89, and to a lesser extent, even 91

BuoyChaser
07-18-2006, 12:28 PM
I believe that's the reason. Engine Nut once posted here that it has to do with assuring that you get at least 87 octane in the engine. So if you know it hasn't been sitting at the station for too long and you plan to burn it all up in a week or so, then it'll probably be alright. As he said (not a direct quote), 87 is fine, 85 is not.
trust me skiing almost everyday, can't tell by my buoy count right now, but the gas doesn't sit in there for very long...

6ballsisall
07-18-2006, 12:51 PM
If I know I'll burn thru the tank in a weekend I have ran 87 octane. If it's going to sit a week before I burn it off I'll run 89. I have ran 91 in it and you definetely can tell between all grades which one provides the most giddy up. 9 times out of 10 I run 89 octane.

MYMC
07-18-2006, 12:53 PM
This has been covered here ad nauseum…. If you want the boat to make less power then run 87, the engine is equipped with knock sensors that will retard timing. This serves as the engines way of protecting itself from detonation from running low octane fuels with high stress loads (i.e. pulling up slalom skiers or running the course at 36mph). However, when the engine pulls this timing out it will make less power…so what you might say? Well it will then take more throttle to achieve a given speed or power output. In other words it will need to burn more fuel to make the power required since it cannot extract it from the lower grade fuel without the possibility of hurting itself.

BTW, as hot as it is this situation only gets worse…hot air doesn’t make power.

Tell your friends 89.

BuoyChaser
07-18-2006, 02:15 PM
This has been covered here ad nauseum…. If you want the boat to make less power then run 87, the engine is equipped with knock sensors that will retard timing. This serves as the engines way of protecting itself from detonation from running low octane fuels with high stress loads (i.e. pulling up slalom skiers or running the course at 36mph). However, when the engine pulls this timing out it will make less power…so what you might say? Well it will then take more throttle to achieve a given speed or power output. In other words it will need to burn more fuel to make the power required since it cannot extract it from the lower grade fuel without the possibility of hurting itself.

BTW, as hot as it is this situation only gets worse…hot air doesn’t make power.

Tell your friends 89.
makes sense especially since skiing 36mph and want times to be good...wonder if that's why we're getting varying times on glassy water with perfectpass...

bdecker
07-21-2006, 04:13 PM
Always run 89 in mine, you might want to tell visitors that cash is better than gas... that way you always know.

Hopefully these boomers don't get in the way of bouys tonight!

Workin' 4 Toys
07-21-2006, 10:23 PM
Just a thought.
How many people run higher than 87. That being said, how long does 89 and/or 91 sit in those tanks going stale.
I do not think 89/91 get used often enough to keep fresh stuff in the tanks and it goes bad. IMO.
I would think thats why a few stations sometimes have ALL 3 levels the same price.
I completely understand the need, but is it what it is suppose to be.:(

east tx skier
07-21-2006, 10:44 PM
Just a thought.
How many people run higher than 87. That being said, how long does 89 and/or 91 sit in those tanks going stale.
I do not think 89/91 get used often enough to keep fresh stuff in the tanks and it goes bad. IMO.
I would think thats why a few stations sometimes have ALL 3 levels the same price.
I completely understand the need, but is it what it is suppose to be.:(

Very good point. Yet another reason to keep stabilizing it. Hold it at whatever I get it at. :o

bigmac
07-22-2006, 12:07 AM
Just a thought.
How many people run higher than 87. That being said, how long does 89 and/or 91 sit in those tanks going stale.
I do not think 89/91 get used often enough to keep fresh stuff in the tanks and it goes bad. IMO.
I would think thats why a few stations sometimes have ALL 3 levels the same price.
I completely understand the need, but is it what it is suppose to be.:(All I've ever used in my boats has been 91 octane non-oxygenated (no alcohol).

BuoyChaser
07-22-2006, 12:49 AM
Always run 89 in mine, you might want to tell visitors that cash is better than gas... that way you always know.

Hopefully these boomers don't get in the way of bouys tonight!
no boomers in the way, just course maintenance...one of these days the accusink will be all dialed in...great havin' you over skiin', always workin' that line...

agree 89 for only a little extra $$$ but sometimes you get guys that just bring the gas...easier for them than the givin' cash....WEIRD!!!

Workin' 4 Toys
07-22-2006, 05:40 PM
All I've ever used in my boats has been 91 octane non-oxygenated (no alcohol).
We have had some bad experiences using 91.

bigmac
07-22-2006, 06:14 PM
We have had some bad experiences using 91.

....and..?

Workin' 4 Toys
07-23-2006, 12:00 AM
....and..?
The discussion was about 87 or 89 in an 05 MCX. Our issues were in carb'd boats and fuel injected vehicles. I was cutting it short sorry.
Point being, unless fuel gets back to 1.29 a gallon for premium and people start using it again 'round here. No sale.
So again, its going to sit in the "bottom of the barrels" so to speak.:(

bigmac
07-23-2006, 08:56 AM
The discussion was about 87 or 89 in an 05 MCX. Our issues were in carb'd boats and fuel injected vehicles. I was cutting it short sorry.
Point being, unless fuel gets back to 1.29 a gallon for premium and people start using it again 'round here. No sale.
So again, its going to sit in the "bottom of the barrels" so to speak.:(
Ah...I hear ya.

I have the 91 octane non-ox fuel delivered to my 150 gallon storage tank every week or two. It's used to fill a few boats - each with 30-60 gallon gas tanks, so turnover in my tank is high. The guy that owns the oil company is a friend of mine, and he assures me he has high turnover in his main storage - or at least he used to. This is a big boating and other OHV recreational area, so premium non-oxygenated fuel was pretty easy to find at the pump, but now that gas is so high, a lot of the gas stations he services are dropping non-oxygenated gasoline because demand is down - the stuff can only be used in motorcycles, collector cars, boats, and off-road vehicles anyway. He may be dropping that particular fuel - especially now that all these stations, all of whom have limited tank storage, have to start contemplating E85. My oil company buddy says no, but I suspect that many or all of those stations are going to strongly consider switching their 91 non-ox tanks over to E85.

http://www.pbase.com/hmac/image/63056377.jpg

He's not supposed to deliver non-oxygenated fuel to private residences, so he has me listed with MNDOT as a marina. He told me years ago that I should expect a visit from the state inspectors, but it's been almost 15 years...

Workin' 4 Toys
07-24-2006, 12:11 AM
In your situation, I'd use 91 or 89 "IF" and only "IF" it held the rating it was suppose to.
I know plenty of folks who drive vehicles that "require" premium fuel because it says so in the fuel door or on the dash. They refuse to run it anymore. They just run like carp. It appears to be an ongoing debate among the high HP guys that shouldn't run 110.
If and when the time comes for me to consider an engine build that makes "X" HP on pump gas, I may consider forcing myself to run it 87, or go to 110.

Of course I will consider E85 if I have the means.....

Leroy
07-24-2006, 12:39 AM
Bouychaser; With this boat....you're kidding! You ski enough I would guess you would know the pull well enough to feel the difference, try a full tank of 87 and then a tank of 91. If your friends see the difference maybe they will not show up with 87 anymore!

Interesting point on varying times. If you use RPM mode and there is less power the actual speed will vary more.

05 ProStar 197 1:1 MCX 350/350; PP6.5ng

[quote=BuoyChaser]so for every 10gals looking at $1 extra for 89.../quote]

bigmac
07-24-2006, 08:58 AM
In your situation, I'd use 91 or 89 "IF" and only "IF" it held the rating it was suppose to.
I know plenty of folks who drive vehicles that "require" premium fuel because it says so in the fuel door or on the dash. They refuse to run it anymore. They just run like carp. It appears to be an ongoing debate among the high HP guys that shouldn't run 110.
If and when the time comes for me to consider an engine build that makes "X" HP on pump gas, I may consider forcing myself to run it 87, or go to 110.

Of course I will consider E85 if I have the means.....Well, it's something to think about. I have always had 91 non-oxygenated delivered because my previous boat called for 91 octane and they recommended against ethanol. My MasterCraft apparently has no such restrictions. Maybe I'll give 89 octane ethanol a try next delivery. If it doesn't work out in the boat, I can always empty it into my truck.

Minnesota is a big E85 state, but there's only one E85 station for about a 100 mile radius of here, and it's 20 miles away and out of my normal traffic pattern. And the difference in price between E85 and 87 ethanol is rapidly shrinking (predictable, of course).

BuoyChaser
07-24-2006, 09:16 AM
[QUOTE=Leroy]Bouychaser; With this boat....you're kidding! You ski enough I would guess you would know the pull well enough to feel the difference, try a full tank of 87 and then a tank of 91. If your friends see the difference maybe they will not show up with 87 anymore!

Interesting point on varying times. If you use RPM mode and there is less power the actual speed will vary more.

05 ProStar 197 1:1 MCX 350/350; PP6.5ng
i honestly have yet to be able to tell the difference...just had 10gal of 87 put in and seemed to burn through gas faster but the engine ran exactly the same...maybe the calibrated PP settings seemed to vary, would the 87 affect that???