What to do about octane?

[Bubba1235]

Engine calls for 91 octane and it is getting harder and harder to come by in my area. (87 and 89 being common.)

What are others doing?

Octane bosasters (what do you use)?

Detune the engine? ugh...

Run what you can find and hope for the best? Double ugh...

 

[Uraijit]

Re: What to do about octane?

I feel your pain. My boat has a 65 gallon capacity, and at current prices, would cost about $253.00 to fill up.

But as they say, "If you can't afford the gas, you can't afford to boat".

Running a sub-grade gas is going to end up costing you more money in the long run when you start detonating the engine. Depending on your compression ratio, you could possibly get away with just retarding your timing a few degrees.

91 Octane is virtually non-existent in my area. The octane rating varies by your location. Some higher-elevation places don't require as high an octane rating, so as long as you're burning 'premium', you should be fine.

Personally, I'm converting my boat to run on CNG (Compressed Natural Gas), it's got an octane rating of about 124, and here in Utah, it's $0.63/gallon... That works out to $41.00 to fill up the same amount of gasoline.

If the conversion works out well for me, I'm going to try and get the kits Coast Guard Approved, and start selling them to other folks who're in our predicament.

 

[paulrfrancisco]

Re: What to do about octane?

I dont think you'd want to use propane, as it sinks in air to the lowest point (bilge).. CNG however is lighter than air...

 

[HT32BSX115]

Re: What to do about octane?

You didn't say what engine...model year model etc....


It must be an old one since most marine engines have been spec'ed for 87 octane for several years.

In 1987 the OMC Cobras had a timing setting for 87 octane. That's your best choice really. I would not trust octane boosters. In a marine engine under load, severe detonation will break or pop a hole in a piston faster than you can pull it back.

IMHO you're either going to have to either re-time the engine or go to something newer that has a knock sensor and/or is EFI etc....


Cheers,

Engine calls for 91 octane and it is getting harder and harder to come by in my area. (87 and 89 being common.)

What are others doing?

Octane bosasters (what do you use)?

Detune the engine? ugh...

Run what you can find and hope for the best? Double ugh...

 

[Squid Billy]

Re: What to do about octane?

I was just going to ask this same question. I just bought the boat 6 days ago and the sticker on my 1972 motor says;

WARNING - Use Leaded 93% Minimum Octane fuel ONLY!

Now What?

 

[Mischief Managed]

Re: What to do about octane?

Maybe it calls for 91 RON. That's the same as 87 RON+MON/2 (or regular gas).

 

[Maclin]

Re: What to do about octane?

Squid Billy,

What brand of engine is it and where was it sold originally?
Does it show the method used to determine the octane on the sticker? There are 2, (R+M)/2 and RON actually more, but those 2 are the ones most commonly used. RON is used outside the US.

(R+M)/2 is what is on the pumps here in the states. 87 would be 91 RON, 89 would be 93 RON, etc.

 

[Maclin]

Re: What to do about octane?

Mischief Managed has the idea, his post was not there when I started, I had my post up while I was eating lunch and had not submitted it until way later.

 

[Maclin]

Re: What to do about octane?

I have a 1991 Volvo Penta 5.7 270hp, it calls for 91 RON or 87 (R+M)/2. It shows both on the engine sticker if you look close enough, the 91 is shown first. I bet 87 is just fine for yours as well.

 

[Maclin]

Re: What to do about octane?

No, it is just a 4bbl carbed 350 with electronic Prestolite ignition. Owner's manual is for a 570A shows 275HP and 91 RON 87 (R+M)/2

I am very sure that any Volvo GM based V8 before 1990 only needs 87 octane.

 

[Maclin]

Re: What to do about octane?

Here is the exact wording from my manual, I had to type it in because the VP site only has this as a scanned in type of document and I can't grab text from it...


Fuel Quality
Gasoline with an octane value of min. 91 (RON) (USA 87
R+M/2). The engines can be run on unleaded fuel.


This manual also covers the 500B and 501B model engines which should include yours.

 

[Squid Billy]

Re: What to do about octane?

Squid Billy,

What brand of engine is it and where was it sold originally?
Does it show the method used to determine the octane on the sticker? There are 2, (R+M)/2 and RON actually more, but those 2 are the ones most commonly used. RON is used outside the US.

(R+M)/2 is what is on the pumps here in the states. 87 would be 91 RON, 89 would be 93 RON, etc.

Hello Maclin,

I am not sure were it was sold originally as I bought the boat used.
I am also not sure exactly what motor I have, but this is exactly that the sticker says;

WARNING - Fuel Required
Leaded Automotive Fuel
Regular or Premium
(93 Octane Minimum -Research Method)​

 

[Maclin]

Re: What to do about octane?

Quote from a technical tuning site.....:

"The number determined in testing using the Research Method is the Research Octane Number, or RON."

So, when it says 91 Research Method that is 91 RON which is 87 here in the US.

 

[Maclin]

Re: What to do about octane?

There is Research Method (RON) and Motor Method both are used to come up with a rating for octane.

The (R+M)/2 formula is simply an average between the 2 methods. R in the formula is RON and M in the formula is Motor Method.

Europe and Australia and maybe other countries post RON values on their pumps. The US and others post the average R+M/2 value on their pumps.


Bottom line, almost all marine engines of that era can use 87 octane unleaded.

The more modern EFI engines with spark knock detection may specify 89 (93 RON) but also have a contingency that states if 89 is not available then using 87 will not be considered misuse of the engine but that lower performance can be expected.

 

[Squid Billy]

Re: What to do about octane?

Ok well would I use or can I use 87 or 89? what about the leaded part of the sticker, or can I use unleaded?


I dont want to fry this lil jewel!

 

[WizeOne]

Re: What to do about octane?

Sorry, 1986 Volvo/Penta 225 (Chevy 305 225 HP)

The manual deffinately calls for 91 octane.

Considering the age of your boat I am sure that the assesment of octane as described above is correct and your motor will do fine with current regular grade gas.

Your 305 chev is only 8.5:1 CR running at 8 deg BTDC. My Ford 5.0 4 bbl has a 9.0:1 cr and runs at 10 deg BTDC and does very well with 87 octane regular.

The only gas concern you have is the lack of lead on the unhardened valve seats in your heads. There are lead substitue additives (nothing to do with octane) that might delay the necessity of having hardened valve seats installed on your cylinder heads.

Someone can correct me if I am wrong but Factories did not start hardening the valve seats until 1975 and often marine motors from Ford and Chevy were actually the previous year motor models. That would make your 305 a 1972 factory production.

 

[Maclin]

Re: What to do about octane?

Bubba's is ok on unleaded 87.

Squid Billy has a bit more of a conundrum. Lead used to effectively raise the octane level, so 87 is ok regarding the octane. However, regarding needing leaded fuel, I am going to stay neutral on that. I do know that leaded fuels have not been available for quite some time so if it is not damaged now (the valves will try to work their way up into the head some) then I do not think running 87 unleaded will do any more harm to it. For peace of mind a modern lead substitute valve lubricant fuel additive may be called for. I am sure the 87 octane is ok.

 

[JustJason]

Re: What to do about octane?

87 is fine... just make sure your timing is dead nuts. If it's knocking at high speed bring it back a few degrees

 

[Maclin]

Re: What to do about octane?

EXactly

 

[Squid Billy]

Re: What to do about octane?

OK Guy's

Thanks!

I will keep an ear out for pings and if so, I will adjust the timing. I might as well bring the timing light with me the next time I go out, looks like fathers day.

Hey, can you guy's tell me what motor I have with the serial # 3332442 ?