94 Octane Marine Gas?

[longshanks]

Where I live in Canada, I can buy dyed gas labelled 'marine gas' for a cheaper price than 'regular' gas. It is dyed purple, but it's 94 octane, compared with the regular stuff which is 89. My boat motors run very well on this stuff. I have heard that this gas is 'hard on the riggin'. I never had a chance to ask what exactly that expression meant. Does anybody have any experience in running it? My motors are liking it so far, even if it's purple.

cheers

 

[Silvertip]

Re: 94 Octane Marine Gas?

For some reason, people generally equate higher octane fuel as somehow providing better performance which is not generally the case. In automobiles, the engine management systems incorporate knock sensors so if higher octane fuel is used, the ECU can advance ignition timing so there may be a slight performance advantage. However, if you have a carbureted outboard, there is no ECU and the engine is designed to run on 87 - 89 octane fuel and there is no advantage to running 94 octane. Two stroke engines run very low compression ratios so pre-ignition is not a problem unless carbon build up gets to extreme levels.

 

[longshanks]

Re: 94 Octane Marine Gas?

thanks for this response Silvertip. The main reason I've been using this gas is because it is cheaper! The one motor that seems to run particularly well with it is an '06 EFI 50HP four stroke motor, I seem to recall the compression is around 180 per cylinder. My main concern is whether or not this fuel could be detrimental to my motors. I recall hearing something about the dye particles clogging carb jets on carb'd motors, or something of the like. Does that make sense?

 

[Silvertip]

Re: 94 Octane Marine Gas?

Those dye particles must be reaaaalllly big to clog a carb jet! Never heard that one. The reason 94 octane "marine fuel" is cheaper than 87-89 octane may be that there are no highway taxes on it. Dye is added so inspectors can sample fuel tanks on commercial and private vehicles to see if they are cheating the government. In some states dye is added to diesel fuel for farm use but the principle is the same. Four strokes do run higher compression than two strokes but again, unless the ECU has a way to detect detect detonation, it cannot change ignition timing.

 

[j_martin]

Re: 94 Octane Marine Gas?

thanks for this response Silvertip. The main reason I've been using this gas is because it is cheaper! The one motor that seems to run particularly well with it is an '06 EFI 50HP four stroke motor, I seem to recall the compression is around 180 per cylinder. My main concern is whether or not this fuel could be detrimental to my motors. I recall hearing something about the dye particles clogging carb jets on carb'd motors, or something of the like. Does that make sense?

To answer your original question. Higher octane is a requirement for more compression or advanced timing. The EFI engine probably actually monitors detonation, and sets mixture and timing to peak efficiency. That's the purpose of computer control from the git go, isn't it?

On the carb motor, no real benefit other than less expense is realized. It does no harm and actually opens up the safe operating range of the engine, temperature, timing, and mixture wise a little bit.

I surely would use it if it were available to me without taxes like it is to you.

hope it helps
John

 

[longshanks]

Re: 94 Octane Marine Gas?

looks like I'll keep pouring that purple gas in my tanks. thanks for your responses guys.

cheers

 

[pecheux]

Re: 94 Octane Marine Gas?

I dont know why ??? but my 15 hp Force runs more evenly at idle with 91 octane gas than with 89 ... could it be the older technologie ? (it's a 1997) I wish that less expensive purple gas was available around where I live ... lol