What Octane and Brand do you use?

Since I seem to be one of the few running 87 octane I want add that I've never encountered any fuel related problems. in the 34 years I owned my car. I'm still running the original injectors, never had the fuel distributor apart. The cars starts, idles and runs without hesitation or misfires. 33k miles and counting. I also never use fuel stabilizer and never worry about how full the tanks are when it's put away for winter. In my 34 years I have had only two issues. One in 2010 when I had to replace ignition wire due to a misfire. The OEM wires were broken internally. The second was last years when I lost a bank due to shorted distributor rotor. Also, I don't buy any particular brand of fuel.

 

me as well

 

Even 87 will make your car perform at least as well as 89.

FWIW: We think of higher-compression engines as having more power - and basically, that's true and why they design them that way. BUT, when you raise the compression in the chamber, you run the risk of the gasoline burning far sooner than it should. The higher the compression, the more likely the fuel will ignite on its own. (This is how diesel engines work. They don't even have spark plugs; the fuel spontaneously ignites because the pressure is so high). So to prevent that, you increase the octane so the fuel is harder to burn. In a lower-compression engine, we don't need the fuel to do that. But 87 vs 91 has no "more energy/power" difference.

Now in terms of gasoline quality and additive (V-nitro, techron, etc) - that's a different issue altogether. None add power, but clean the internals. Many places like Shell may only offer those additives in 91 octane. So there's an advantage in getting 91, but only for the additives. You could also just use 87 and buy a bottle of techron every few months and pour it in. If your car runs better on Shell 91 vs Costco 87, it's because the gas quality and additives are better - but not the octane difference.

I've used pure non-ethanol on a few occasions, love it. Absolutely can feel the power difference. Smells nice, too. I'd use it all the time if the station was a bit more convenient to me.

 

Just for clarity gas doesn't burning faster than it should in a high compression engine when running too low an octane. Gas burs at the same rate regardless of octane rating. What happens is that the temperature of the unburt part of the mixture increases in temperature due to a couple of effect and if the temperature rises above the detonation point the remaining mixture explodes all at once. So you go from a control burn to an explosion. Knock is due to this expolsion and the shock waves that propagate through the combustion chamber.

There are basically two factors which contribute to raising the temperature of the unburned mixture above the detonation point. One is the obvious compression due to the piston coming up. This sets the basic pressure in the cylinder but it alone will not generally cause detonation with low octane fuel. The other is a little more complicated but it is why retarding the ignition can prevent detonation. At some point in the compression cycle a spark ignites the mixture. A flame front propagates out from the point of ignition. The mixture on the back side of the flame front has combusted, raising the temperature and pressure of the burnt mixture. This cause the burnt gases to expand compressing the remaining unburned mixture further. This additional compression raises the temperature of the unburned mixture further with the possibility of exceeding the detonation point. It's not just the compression due to the piston coming up. Now, timing of an engine is set so that all the fuel is burnt at a specific point in the cycle (over simplification, ). The fuel burns at the same rate regardless of RPM. So if you want to complete the burning process at the same point in the cycle regardless of RPM you have to ignite it sooner at higher RPM because the piston is moving faster while the burn rate is constant. However, by retarding the ignition the burning process is delayed. The combustion process won't be completed at the desired point in the cycle and you loose power. But by the same token, by delaying the start of combustion the increase in pressure in the cylinder due to expansion of the combusted part of the mixture won't rise as high and detonation is avoid.

 

So you think 89 is okay for our Euro carb cars...I never tried it and assumed 91 was better, but I'm happy not to waste the money if not needed. That and I'm not sure with US gas...

 

What Johnk said... Image Unavailable, Please Login

 

I have a few Maverik stations near me that are ethanol free. I believe it is 88 octane but my rationale is that it will keep the fuel lines from being eaten up.

 

I've been running E10 in y 308 since 2004. Never encounters any type of ethanol related problem of any kind: hoses, injectors, tanks..... I have a bottle of E10 sitting in my garage with a small vent in it to mimic a fuel system vent. I've been watching it for 5 years now, looking for separation. Nothing but a little evaporation from the vent.

 

+1

E10 since 1999 and earlier with previous owner in my 328

 

i've been using eth-free fuel in gabriella, an '87 328. she has no cat and smells at stop lights,etc. i have no idea the brand as i buy from a fuel distributor.
the pump says 91 octane. it is unleaded.

 

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I correct here below my previous post:

standard Euro unleaded fuel 95 RON for the NA 308 engine. SHELL V-POWER 98-100 RON (or another 98 RON brand) for the 208 turbo (almost mandatory for the first 1982-1985 model, highly recomended for the 1986-1989 model).

ciao​