correct octane

[JB]

Re: correct octane

Amen!

 

[krosemond]

Re: correct octane

ODDD1..Thanks for the insight.<br />Here you go: 20' Robalo CC skiff 3500 pounds wet, 150 1979 Johnson, 25mph on plane at 3700 RPMs. I don't push it, except when I am trying to get the older kids up on skis at the lake. Mostly I use it on the NC Coast, inshore and nearshore (except for the occassional summer day when i can get 15-20 miles off to the 20 fathom curve for a dolphin or two). I inherited it 3 years ago, and brought it back to running condition after a long sleep of 7-8 years. I think Dad was a turnkey kind of guy, so there wasn't much maintenance, and I don't think she asked for it while he had it. It has been running fine except for a few glitches this early season, but with a little prop work, I should be on track for the summer. Estimated hours around 1000-1200 on the engine. I have thought of a repower, but this ol' Sea Horse just won't give up. So I want to do the things that make it last, keep it safe and reliable. Having said all that, what do you recommend for octane? I have been running 92 until recently and went to 89. I can't tell a performance change.<br /><br />Cheers!

 

[Jersey13]

Re: correct octane

I thoroghly enjoyed this thread. You guys are worth the weight of gold with all your knowledge. ODDD1, Dhadley, J.B., 12Footer...Funny, a week ago i was just discussing this whole octane topic with one of my buddies, and now i get a few experienced "expert" thoughts on the matter. It's amazing to me how many people put 92 "high test" in their cars/trucks/boats no matter what year, make or model. They just figure it's going to be he fastest and cleanest buning fuel for whatever they own. Then, 2-5-10 years down the road when they blow something they don't understand why. They've used "the best" fuel, right? wrong...in my book anyway. Backing up what 12Footer stated - The correct fuel to use varies for whatever application you're using it for and where. Thanks again for that "technical" dicussion. I really enjoyed it

<br /><br />- Jersey

 

[uflanke]

Re: correct octane

Okay, just one more question...<br /><br />Miller Lite: Taste's Great or Less Filling?<br /><br />Just Kidding

 

[12Footer]

Re: correct octane

Tastes Great

<br /><br /><br />------------------<br />the Early bird get's the worm...So, he don't have to stop for bait.

 

[ODDD1]

Re: correct octane

Well, krosemond you got an older girl there... definately get a pat on the back..most guys that get motors this situation get them started and burn em down...is older probably got some carbon deposits in it[not necesarily a bad thing]you are a prime candidate for premium fuel...besides it has served you well in the past, hasn't it? The only big difference ihear people beef about is [of course] cost......10 cents price spread between the 2 fuels..you know how much fuel you burn a year..what does it add up to, and are you willing to pay it? You can use the same reasoning for oil too..how much more a year do you really pay for the good stuff?

 

[JB]

Re: correct octane

Less filling.<br />JB

 

[fordman]

Re: correct octane

Well I ran 87 octane on my last trip. The boat not only ran much better than with 92, I didn't have any of the black residue on the transom.Thanks for the help.

 

[krosemond]

Re: correct octane

ODDD1 I tend to agree with you on the ROI of using quality products, so long as they are correct. My fear was that I was doing damage to the ol' girl. I am not a mechanic, but I have spent alot of time on the water, and know some good tricks with a hammer, wd-40 and some duct tape just to get home. My problem is all my experience was with a volvo tmd40 single inboard, and it just ran without a lot of fuss. I am trying to learn as much as I can about Outboarding, but it is a different game.<br /><br />Thanks for all the input from everybody. Maybe at some point I can add some value to the discussion.<br /><br />Ken

 

[mtp]

Re: correct octane

Ok, I haven't seen anyone mention this one. The 92 ocatane I used in 88hp OMC ('93) "ate"/degraded some of the carb gaskets. Pieces plugged the high speed jets and (obviously) did a number on performance, got home at 1500 rpm - slow 5 mile cruise. Replaced the gaskets, cleaned out jets and have been running midgrade (87) ever since. No degradation/breakdown. Could have been bad gaskets, but have a friend w/ newer Mercury who had the same problem/same solution, same results.

 

[ODDD1]

Re: correct octane

MTP, you are missing one factor....fuel formulations have changed ALOT in the last ten years...newer fuels eat up alot of stuff we thought was ok for the last 40 years...

 

[ODDD1]

Re: correct octane

MTP, you are missing one factor....fuel formulations have changed ALOT in the last ten years...newer fuels eat up alot of stuff we thought was ok for the last 40 years...

 

[ODDD1]

Re: correct octane

MTP, you are missing one factor....fuel formulations have changed ALOT in the last ten years...newer fuels eat up alot of stuff we thought was ok for the last 40 years...

 

[ODDD1]

Re: correct octane

Hey, I"ll try screwwin up even worse next time......

 

[sony2001]

Re: correct octane

ODDD1: Earlier you wrote the if the puter doesn't get detonation with an advanced timing it will think the sensor is malfunctioning, thus retard the spark. So <br />if everything is well the puter will make it worse? Please explain.<br /><br />------------------

 

[ODDD1]

Re: correct octane

Sony, you gotta understand a few things first....ANY motor, 2 or 4 cycle, will make its best power, most effeciently, with a lean enough mixture and enough timing advance that it will ALMOST detonate, but not quite. the whole purpose of electronic engine management is to achieve this goal.....because of all the variables the engine sees it must be able to change the fuel mix and the ignition advance..and it must be able to tell when it goes too far[the engine starts to detonate]. so what happens every time you run your fuel injected mercruiser....once under power the puter advances the igition till the detonation sensor tell the puter the engine is detonating then the puter pulls timing back JUST ENOUGH TO MAKE IT STOP and you have the most efficient burn.....now if the puter can advance the timing enough to make the sensor "detonate" it thinks something is broke and runs on a 'failsafe' setting that is not as efficient....this is what happens when you run 92 octane in these motors......

 

[Wink]

Re: correct octane

hs anybody ever run AVGAS (Aviation Fuel in an outboard, it seem far more stable than normal gas station fuel. Juat a ?, have enjoyed reading all previous posts!

 

[corm]

Re: correct octane

Avi-fuel has a different specific gravity than auto pump fuel. So I don't feel it is worth the trouble to redo the carbs to make it work correct.<br /><br />As my $.o2 on this octaine post. I Never run the mid grade fuel with 10% alcohol in it. It will absorb water from the air and plug the carbs up. Also most I've seen tested has more that 10%. Many motors have melted pistons with this fuel.Alot of times people pump water into their tanks rite a the gas station.<br />Mercury says that when your fuel is 2wks old it is already droping in octain do to the aromatics that are added to boost the octaine<br />evaporating.<br />Here in Wisconsin, in the spring we still get "winter blend gas", a mix that will allow your car to start when the temp is below 0.<br />If this is use in your boat you won't be able<br />to plane your boat out as it is all aromatics<br />and little real fuel. <br />In pre 1977 motors I tell people to run the highest octaine they can get. The new motors were made to run on the lower octaine fuel and I recomend to customers to run it.<br />I run Turbo-Blue race fuel in my 76 L6 Merc with the timing advanced 5.5 deg. I also reworked the water sys to get another 6lbs of water pressure to help keep cyl 1,3,5 working with an XS trigger plate. Runs fast

<br /><br />corm<br /><br /><br />btw, if I can find the tech web site again on the different fuels and effects I'll post it.It got moved and I can't find it now.