What Octane?

[Captn Dave]

I've got a question for everybody.<br />What octane gas do you use in your outboard?<br />I know what is recommended for our relatively low compression engines. But I've heard different rationales regarding the use of higher octance gasoline. <br />Some say the slower burn of higher octane is better. Some say higher octane gas is of better quality.<br />But I also know a commercial fisherman who uses nothing but 87, racks up a ton of hours, and has never had a problem.<br />So sound off and let's hear your reasons and experience.

 

[dragula65000]

Re: What Octane?

Well, in my truck I try to run 89 because I have a higher output ignition. Depending on the ignition output, you'd have to run a higher octane so it won't detonate and turn the motor into a grenade. But on my 175 johnson I run 87 octane. I don't have any upgrades to it, and it ran fine before my power pack crapped itself. But with a lower octane and what weather you store your boat in, it tends to jel a lot faster than higher octane. I also would not recommend running anything over 93, because the motor will run so hot you can burn it up on one run, or worse. Just a thought.

 

[Dhadley]

Re: What Octane?

87 is fine in most recreational and commercial outboard motors. <br /><br />Todays higher octanes burn hotter, not cooler like they did in the lead days. Combustion temps are very critical. Thats why you want to make sure of the octane level, correct spark plug, correct timing, correct fuel mix (jetting), cooling system and especially the correct (capable) rpm.

 

[ZmOz]

Re: What Octane?

Using anything more than the minimum is a complete waste of money in an outboard, especially considering how much gas they use. I use 93 in my '74 inline 6, but that's because it was designed for a minimum of 90 leaded, and has a reputation for burning pistons.

 

[JasonJ]

Re: What Octane?

I use 87 in everything. Unless you have advanced the ignition, increased the compression, or have forced induction the higher octanes will do nothing or even inhibit performance. There is also a common misconception the higher octane gas is cleaner which is false. All octanes have the same cleaning additives, the only difference is the octane. I hear so many people say they use higher octane because it is cleaner. You actually can end up with deposits from unburned fuel from the higher octane which over time build up, causing an increase in the compression ratio, which causes you to end up needing the higher octane. On a stock engine, anything higher than minimum octane and you may as well just take your money and light it on fire. Gas prices are high enough, no need to waste any more than we need to.<br /><br />Dracula, unless you have advanced that ignition, the higher output of it has no bearing on what octane you use. Octane is meant to suppress the burn. Advanced ignition, higher compression ratios, and forced induction are the only reasons for higher octane because those conditions allow for the air/fuel to become hotter thus being more susceptable to pre-igniton. Just an increase in igniton power alone does not necessitate an increase in octane. Have you tried it on 87? If it does not ping under load, thats all you need.

 

[dragula65000]

Re: What Octane?

I started running 87 because of these gas prices, and have actually lost a little mileage, and some performance.Nothing drastic, I have a truck. It's not like I'm taking it to the track on saturdays. But with the higher octane in my truck, I do notice better performance. Not much, but it's there. For some reason, when I ran 89, then went to 87, then to 89, something would always go bad with my exhaust or fuel system. It most likely needed to be repaird, but on all my vehicles I had that happen. Maybe it's just me.

 

[rickdb1boat]

Re: What Octane?

Compression is the key. Your outboard has nowhere near the compression of your truck. It cannot take advantage of the higher octane and will not burn it off, leaving unwanted deposits in your combustion chamber and rings. Not good...

 

[UpstNYer]

Re: What Octane?

I had been reading in various places here that the higher grades were more stable for long term storage. Last fall, before putting the boat up for the winter I went to the Sunoco station to fill up the internal tank. For some reason that day, the Sunoco top grade (93 Octane I believe) was going for $.04 less per gallon than the mid-grade (??) so I filled up with that.<br /><br />Had a new 90HP Classic Merc installed in March. The dealer mixed Quicksilver Premium Plus with the gas in the tank to give me a 50:1 pre-mix for breakin (in addition to the oil injection).<br /><br />For breakin I've kept it at or below 4200 RPM and have spent a lot of time chugging around at 2300 to 2800RPM just below plane, because the water's been rough. Boat is a 16' Fisher Aluminum Deep-V. No alarms or anything, lake water still very cold and engine seems to run fine.<br /><br />Am I harming the engine with any of this? Is breaking in on that 93 Octane going to cause problems down the road? This is the biggest, newest outboard I've owned and it's got to last me awhile.<br /><br />Thanks. <br />Bob

 

[RJS]

Re: What Octane?

I have always read to go with the octane rating your manufacturer recommends. I use 87 and a gas stabilzer.

 

[Dhadley]

Re: What Octane?

The higher octane will not retain the oxygen bearing compounds (that create the higher octane rating) any longer than the 87. They both return to base line fuel in the same time frame.

 

[Buttanic]

Re: What Octane?

Wave, I did a search for Chris Craft Cutless and found that you have owned one. I am thinking about buying one that needs restoration and would like an opinion about the boat.You can e-mail me at tmadere@bellsouth .net