What kind of gas ?

[ThomasBorchers]

Hello you all !

I own a 1955 Buick Century. I always take normal unleaded gas for this car. Some days ago a guy said that I have to use premium or I will ruin the engine.

What would you say : for the 1955 322 cui engine : Unleaded or premium gas ?

And : Was there a very high octance gas in USA available at gas station or just the normal premium we use today ? Since when was "Premium" gas available in USA ?

Greetings

Tom

[Matt Harwood]

Octane is a funny thing in that almost nobody understands it. But the bottom line is that gas today is vastly superior to even what they were using in 1955. If your engine isn't pinging on regular, then everything is fine--premium will just be throwing money away. But if you hear detonation (say at the top of 2nd gear at full throttle), then you may benefit from more octane. Go to a mid range grade and see if it improves. If not, step up again and reevalutae. But if it runs OK on regular, then you'll have no problems. How much compression does your motor run?

People like to think that premium has more cleaners or comes from a better grade of oil or makes horsepower or other magical properties, but the only thing that is different is the addition of more octane--a catalyist that raises the fuel's flashpoint, thus making it more resistant to hotspots that cause detonation. It doesn't take part in the combustion reaction, either, so you won't get any more horsepower from it. If you don't need it, you'll get exactly nothing except a lighter wallet from using it.

Here's more information I wrote about a year ago: Spinning My Tires: Debunking Some Automotive Myths

Hope this helps.

[ThomasBorchers]

Hi Matt,

thanks for the answer. Compression is 9:1.

Engine runs actually good. If I press the gas pedal a bit more I hear a sound like a race engine or so. Sounds hard... like roooar.. or so.

Greetings

Tom

[Matt Harwood]

Detonation will sound like marbles rattling around in a metal coffee can, not like a race-car roar! At 9:1 compression, 87 octane should be sufficient for anything but towing a trailer through the desert.

Glad I could help.

[old-tank]

Hi Tom

All of my 55's run well on 87 octane unleaded except during the summer months and using the factory air conditioning, when I then use the mid grade unleaded 89 octane.

Another indicator of too low octane is dieseling or run-on after turning off a hot engine and sometimes you will hear a crack sound as a hot engine first starts.

Enjoy!

Willie