I have a 1966 Mustang coupe, 2 barrel 289, and was wondering if there would be any benefit in using the higher, and more costly, octane gas. Currently, I am putting the highest grade gas into the car, mostly because I think that it will keep the valves and cylinders cleaner. But, recently I began to think that these higher octane gas didn't exist in 1966 and maybe I might be doing more HARM then GOOD.

What is the opinion of the experts here on the forum. Thanks.

 

You're not doing any harm, you may or may not be doing any good. Use the lowest grade of gasoline that does NOT cause your engine to ping, or pre-detonate.

If under moderate to high load there is no pinging, you're all good.

BTW, octane ratings were different when these cars were new, I'm not sure if there is a direct correlation. Also, lead was added in the old days.

 

The rating today is much different today versus then.
The 1966 owner’s manual states that a 2V 289 requires 94 minimum octane back then. The 4V and HIPO required 100 or better.
Like Axeman says use what works best in your car.

BTW higher octane doesn’t necessarily mean the "best" gas. Depends on the additives the maker adds when refining.

 

Your 2V should run perfectly on pump regular. My 289HP is just fine on pump premium, and I could probably get away with less in needed.

 

Okay thanks. So, then what manufacturer and grade does everyone use?

I live in Canada, so I have to choose from Shell, Esso, Sunoco, Petro Canada, etc...

Recently, Shell started advertising Nitrogen enriched gasoline. Does anyone believe this would be a benefit to this old engine?

Thanks.

 

Don't know about the nitrogen enriched gas, but a friend of mine who drag races once dyno tested different makes of pump gas in his 1000hp car, He found that Pioneer was giving him the best and most consistent response, but all the others were close behind. Unless hundredths of a second matter to you, it doesn't really matter which brand.

 

Now that's funny. Nitrogen is an inert gas. 78% of what you're breathing in right now is nitrogen.

 

The correct answer:

I run 87 in my 302 and it's really smooth. Gasoline is different from state to state with some states like CA requiring "cleaning" additives. Some discount gas vendors like Pioneer and Arco might not offer the same quality as the big boys like Exxon and Unocal. There's no one answer for all cars.

CP

 

My 65 289 2 barrel runs best on Shell Premium. Without ethanol when I can find it, which is basically never these days.

 

I've had 4 Vintage Mustangs over the years, 2- 200 C.I.6 cylinder cars, and 2- 289 V8 (1 2bbl, 1 4bbl). All of them ran just fine using regular unleaded gas. Never had any problems using regular.
Hope thet helps.
Jay