Fuel Grade

[EricKit]

Hello, I was wondering what type of fuel I should put in my 1973 Ford 302 Engine. I used the lowest grade once, and had no problems.

As I understand it, the only difference in the rating of fuel is the autoignition temperature of the fuel. The higher the grade, the higher the temperature. This prevents knocking (Where the fuel ignites before the spark plug) since autoignition temperature is inversely proportional to pressure of the oxygen around the combustable material. With a low grade you risk that compression causing an off timed ignition of the fuel. Since I got no knocking with my boat, I figure going to a higher fuel grade will not benefit me at all.

The reason I'm asking is because I don't know if there are other benefits to going with a better fuel (additives, less deposits, anything I'm not thinking of). Thank you for any help.

 

[Gary H NC]

Re: Fuel Grade

If it runs fine on 87 octane then no need to waste money on the premium gas..
Most boats are designed for regular anyway.

 

[EricKit]

Re: Fuel Grade

If it runs fine on 87 octane then no need to waste money on the premium gas..
Most boats are designed for regular anyway.

Thanks, that's what I was hoping!

 

[boat1010]

Re: Fuel Grade

I usually just use the lowest grade in mine too but I can tell the difference when I use the higher octane in my 7.4. But I just cant afford to us that when it takes 70 gal. to fill it. Just my $.02 worth...

 

[Jeepster04]

Re: Fuel Grade

Compression plays a major role in the amount of octane needed also. The more compression the more heat so pre ignition can occur. If its not pinging on 87 its fine.

 

[dubs283]

Re: Fuel Grade

the main concern with using regular "pump" unleaded gasoline is the amount of ethanol/alcohol in it

the alcohol in fuels will attract water and cause runnability issues and possibly damage fuel system components

depending on what state you live in/purchase your gas the ethanol/alcohol content can vary

you are best off using fuel that is classified as "non-oxy" meaning it has no ethanol/alcohol in it

 

[Jeepster04]

Re: Fuel Grade

the main concern with using regular "pump" unleaded gasoline is the amount of ethanol/alcohol in it

the alcohol in fuels will attract water and cause runnability issues and possibly damage fuel system components

depending on what state you live in/purchase your gas the ethanol/alcohol content can vary

you are best off using fuel that is classified as "non-oxy" meaning it has no ethanol/alcohol in it

Very good point. Pretty sure were fighting ethanol problems right now with our boat. Engines ran great all summer then towards the end of the season they all 3 started running bad. Rough starts, rough idling, etc. Probably end up pump all 100 or so gallons out.

 

[zbnutcase]

Re: Fuel Grade

Is your boat a 73 or 77 as it says on the bottom of your post? Hope 77 because 73's don't have hardened valve seats for unleaded fuel. 'nutcase

 

[bruceb58]

Re: Fuel Grade

Is your boat a 73 or 77 as it says on the bottom of your post? Hope 77 because 73's don't have hardened valve seats for unleaded fuel. 'nutcase

For the amount of hours most run their boats it is not a problem. Even if it was, you run the boat until the valves go and then do a valve job.