Does 87 octane boil easier than 91 or 93?

[timk225]

I originally had a problem with my 1973 Dusters' 225 pinging easily, even on 93 octane. I reduced the initial ignition timing to 3 degrees. Then more recently, I replaced the intake valve seals, 3 of them were cracked pretty good and were very old.

So a couple days ago, with the gas tank near empty, I decided to test the engine with 7 gallons of 87 octane, it shouldn't need more octane than that.

And over the last day or 2, if I'm near the car 10-20 minutes after driving it for a while, I can smell the gas fumes. Today I looked at the 350 Holleys' sight glass, and I could see the fuel bubbling in there with the engine turned off.

I never noticed this with 90 octane ethanol free or 93 octane gas. It is just the more volatile 87 octane not handling the engine heat as well?

 

[AJ/FormS]

Just so you know, I've been running 87E10 full-time in all my cars since 1999, when it came to our area.
Even in my hotrods.


If the fuel is boiling in the bowls, you have to ask yourself if it is also boiling in the line, between the pump and the carb.
Or maybe, it's just sucking air somewhere, like at the rubber-jumper, coming off the sending unit back at the tank.

Yes the lightest components of gasoline begin to boil as early as 95*F, at standard temp and pressure.
But, in the line from pump to carb, that should be at or near 4psi, which will raise the boiling point....... unless you're at elevation.
I live in Manitoba Canada.
I run my engine at 207*F .
Summer ambient temps can be as high as 99*F, and can run up there for a week or more.
My headers are unwrapped, and and at 7000rpm, are like hot-lava, lol.
But, my 750DP is getting fresh "cold air" from above the hood.
She has no heat-related problems.
well, she has no problems at all, lol.

Happy HotRodding

 

[RustyRatRod]

 

[Dana67Dart]

I have a video ( it's on FABO somewhere) of my formerly clear fuel filter draining of liquid fuel but maintaining 5-7 psi in the line between it and the carb. Once the bowl got low enough the valve would open, the vapors in the filter would rush into the bowl and liquid fuel would follow.

That was 85 octane standard pump gas with whatever alcohol is in it

I switched to alcohol free and can't make it happen now.

5000 foot elevation, stock 67 dart 273 2 bbl automatic, no fan shroud, 7 blade fan, stock fuel routing and pluming, only standard thin gasket between carb and intake.

For me I think it is the alcohol. As the only thing I changed was the fuel.


Google search says lower octain has a boiling range lower than higher octane fuels.

But notes that each has a range due to the other chemicals in the fuel.

 

[timk225]

My fuel system is all new, assembled about a year ago with about 1800 miles on it. I've got a factory style fuel pump on the Slant 6, not high volume or pressure or anything like that. Fuel filter down by the pump, metal filter, of course. Rubber fuel hose up past the alternator and over the valve cover to the carburetor.

I'm sure the fuel can get heat in it, but I would think less heat than a typical metal fuel line wrapping around the front of the engine within 2 inches of the exhaust manifold.

 

[Newbomb Turk]

I originally had a problem with my 1973 Dusters' 225 pinging easily, even on 93 octane. I reduced the initial ignition timing to 3 degrees. Then more recently, I replaced the intake valve seals, 3 of them were cracked pretty good and were very old.

So a couple days ago, with the gas tank near empty, I decided to test the engine with 7 gallons of 87 octane, it shouldn't need more octane than that.

And over the last day or 2, if I'm near the car 10-20 minutes after driving it for a while, I can smell the gas fumes. Today I looked at the 350 Holleys' sight glass, and I could see the fuel bubbling in there with the engine turned off.

I never noticed this with 90 octane ethanol free or 93 octane gas. It is just the more volatile 87 octane not handling the engine heat as well?

With pump fuel it’s a crap shoot. You can buy fuel from three different places and get the exact same fuel and go to a fourth and it’s different.

You would need to get a distillation curve from the blender of the fuel, and it needs to be that fuel from that blend. And the blend changes pretty regularly.

That’s why the money saved isnt worth the crap shoot. Especially since pump fuel is always blended for EFI.

 

[413]

It is the alcohol doing it. So go with ethanol free fuel. Makes a big difference in my experience.

With alcohol fuel They cheat to get the octane higher with the alcohol. They can't do that with ethanol free fuel.

 

[CRUZE 418]

In two of my cars, one is straight premium, the other 10% gasohol. It doesn't make any difference, they both spin over until they get gas again. The only thing that has cut that spin time down is opening the hood and let the heat out. Gas is different in all regions of the country. Some gas, like here all comes in on the same pipeline. Then gets additives. I hauled gas to stations for a couple of years. For what it's worth.