Best octane?

Again, check out the link I provided. It is true the term Octane in fuels originally came from the chemical composition that related to flashpoint, but it no longer relates to the actual chemical composition when relating to fuels. Now it simply defines the flashpoint at pressure.

As a matter of fact, different engines will grade the same fuel at different octane rating, which is why there has been differences in rating a fuel's octane.

 

Hi Dave:

<div class='quotetop'>QUOTE(DaveinOlyWA\";p=\"96576)</div>

Well, the problem with alcohol fuels is the vapor pressure at lower temps. The manufacturer usually has two options:

1. “Excess fuel†enrichment. Think of something like a Mercury outboard. When you push the key, instead of operating a choke you activate a solenoid. This squirts raw gas mix into the motor so it starts well when cold. If you forget to squeeze the primer bulb first, there is no residual fuel pressure and the outboard will just crank.

You can accomplish almost the same thing by playing around with injector pulse width to dump a lot more fuel into the motor. Excess fuel must do wonders for cold start emissions, so I really don’t see this being used.

2. Small reservoir of “real†gasoline for cold start and warmup. Usually a 1-5 litre reservoir, the motor has extra temp sensors so based on a combination of ambient and motor temp, it can switch fuel valves to start the motor on “real†gasoline, then once it begins to warm up it will switch to E85.

Seems like an awful lot of extra work. You’d also have to have two separate fuel/timing maps to contend with. But I guess it has to be done. The thing that I’ve noticed running Mohawk 90 with 10% ethanol is that an EFI motor will usually start *better* in very cold temps.

<div class='quotetop'>QUOTE(DaveinOlyWA\";p=\"96576)</div>

Hmmm, jet fuel. How can I break this gently?

It seems most of the civilian population has this weird conception of “jet fuel†as something really exotic or dangerous. Civilian airlines run Jet-A, which is nothing more complicated than highly refined kerosene. As a light distillate, it has quite a bit in common with diesel fuel.

Back in the 70’s my dad had a remote cabin in North West Ontario, and we’d have to fly to it in a Cessna 150 float plane. He really liked flying before his health problems caught up to him. He always brought along a couple of 5 gal pails of Jet-A.

He used to get the Jet-A from a helicopter survey company in Utah. Once Jet-A has more than a minute trace of moisture it can’t be used, so they would usually give away the “contaminated†fuel or sell it dirt cheap. A lot of it was used by rail locomotives, the motors ran just fine on it.

We used the Jet-A in the oil lamps and also in an old Winco genny. The Winco had a Briggs & Stratton Dual Fuel motor: you’d start it on gasoline, then once it warmed up you’d move the fuel lever to switch the motor to kerosene, which is the same as Jet-A. It would be impossible to start on kerosene, I know I tried a few times by mistake.

I remember how the motor would suddenly run quieter, smoother, and much cooler once the motor was warm and I moved the fuel lever over. For an air cooled motor, that really helps extend the life of it. The exhaust was typical diesel exhaust.

Funny thing is, whenever we told folks back home – in Utah – that we filled the oil lamps with Jet-A, they’d freak out. “Didn’t the cabin explode?â€

About the only thing you have to watch is that a lot of Jet-A is blended with Prist, which is an anti-ice additive. I think most modern turbofans have Prist dispensers onboard, but a lot of helicopters don’t. I don’t think the Prist fumes (Diethylene glycol monomethyl ether ) from an oil lamp helped any, that’s for sure.

I doubt you did any harm to the Camaro running Jet-A through it. It would have been the same as accidentally filling the tank with diesel from the truck stop.

I am curious why you just didn’t try AvGas? Aviation Gasoline is 110-120 octane with lead, so assuming that Camaro had pop-up forged pistons and 10:1 or better compression, it would have run very well on AvGas.

Jay

 

Oops! I've been using high octane in my Prius (since I bought it in August of 2004), both on the advice on the salesman and my brother (the car "expert" in my family. Have I already damaged my car? Should I do anything special before switching to a lower octane? Is 85 too low?

Thanks for your advice!

 

Oops! I've been using high octane in my Prius (since I bought it in August of 2004), both on the advice on the salesman and my brother (the car "expert" in my family). Have I already damaged my car? Should I do anything special before switching to a lower octane? Is 85 too low?

Thanks for your advice!

 

No, you didn't hurt anything, but you're spending more money than you have to on fuel.

85 at higher elevations is like 87 at sea level. Try a tank or two of 85 and see how the car likes it.

 

I don't think he meant jet fuel, which as you say is similar to kerosene. Perhaps he meant avaiation gas, which has an octane rating of 104, if I remember correctly.

 

No, his exact quote was "another thing about the use of high octane gas. several years ago i had a "quasi-legal" access to jet fuel."

My Dad used to also get AvGas from the small airport and we had no problems running it in lawnmowers and gennys. He used to also save the fuel he drained off from the wing tanks to check for moisture, instead of just throwing it on the ground.

About the only problem I can see AvGas causing is the older high lead AvGas. You will have to change your plugs a lot more frequently, since they will become fouled with lead ash deposits. Of course, AvGas should *never* be used in anything with an O2 sensor or catalytic converter.

I know some car collectors who run AvGas in their cars made before 1970. They're worried about valve damage from trying to run an old high compression V8 on unleaded, and for as often as they get driven it really isn't viable to pull the heads just to get harder valve inserts.

Especially in the car Dave descibed, a hot rod Camaro, I have to assume pop-up forged pistons and at least a 10:1 compression ration. Maybe 12:1. So it should have run very well on AvGas, especially the older high lead +110 octane AvGas.

 

it was a fast car... oost me $9500 @10 years old when a brand new one could be had for $6000. and it was jet fuel. we were in So. Cal and Aviation fuel wasnt very available at our base. we had it but didnt host a plane that used it so it was too controlled.

we did have a civilian flight school there but they kept a pretty tight control on their stuff. on the military side, you could get anything you wanted if you had a couple cans of coffee

 

Dave:

Well you didn't do any damage to the car. Just like trying to run it on diesel, the plugs needed to be changed.

I'm also not surprised the points got burned, only a high voltage CD ignition like an MSD would have been able to spark the plugs without damage.

Otherwise the coil saturation would have been very high and the points would have quickly pitted.

Jay

 

Is all avgas now unleaded? For a long time, you could get "low lead" avgas, which had enough to help with the valve seat problem. A few foolish souls tried it on a cat-equipped car, much to their expensive regret.

 

it wasnt when i was there. although this was before unleaded was required. this was the late 70's so we still had leaded gas then.

the only reason i tried the stuff was because you could get 101 octane gas if you didnt live in CA. so i figured high octane was better...(hey i worked in the avionics squadron... to me gas was gas...)

before the Camaro i had a AMC Javelin (ok no laughing!!) and ran 101 in it all the time but was living in Mich then.

 

It all depends on the color, though I'm a bit hazy on this as I haven't flown in a long time.

Red: around 87 octane and low lead, with mixture at Rich
Blue: around 100 octane and low lead, mixture at Rich. Most common?
Green: around 130 octane and highest lead, mixture at Rich

Also, since small aircraft can expect to be operated up to 8,000 ft, higher with oxygen onboard, the vapor pressure is quite a bit less than automotive gasoline. So even if your car doesn't have O2 sensors or catalytic converters, it may not run very well on AvGas.

 

<div class='quotetop'>QUOTE(avboone\";p=\"97573)</div>

It depends on your altitude. Colorado Springs is 6000 feet; the regular gasoline is 85 octane. On the advice of our salesman, we filled the tank twice with 87 octane before the good people at PriusChat and PriusOnline convinced us that 85 octane would be fine. So far, they're right.

 

<div class='quotetop'>QUOTE(avboone\";p=\"97573)</div>

It's in your Owner's Manual, and on the back cover on what fuel you should use.

You could give your salesman and brother a good yelling to get back to school.

 

Well, my owners manual says to use 87 octane or better. Seems to me, you could use premium if you wanted to, but didn't say not to. Anyone here have troubles, or have a light come on using premium? Mine works great using 87 octane.

Ron

 

You shouldn't have any trouble running 90-92 octane instead of 87 octane, it's just that you won't have any benefit either. Why pay more?

The exception is the 2000 GMC Sierra pickup I had. I normally ran the cheapest gas I could, except when towing 8,000 lbs. Then I ran Mohawk 94 octane. The pinging disappeared and the truck had a bit more power and slightly better fuel economy.

Otherwise, run the lowest octane recommended. If you do experience pinging/detonation, go up one grade, eg 87 to 89.

 

anything too high octane and you run the chance of having starting problems...

 

Well, I would love to see somebody try to start a bone-stock car on 130 octane.

With my 2000 GMC Sierra, I didn't notice any difference in starting whether it had 87, 90, or 94 in the tank. It always started instantly.

 

Well, I just put in my first fill last weekend, and used the 87 octane. I have read here and else where, that using 91-92 octane could set off the check engine light. So forget about that. Besides its more money for nothing, at least on the Prius.

 

jayman, my husband just borrowed a hybrid training book from his friend who's a Prius Tech.

there was a strong warning in there that using gas with an octane rating over 87 can cause starting problems in the Prius, and that's what i was referring to.

i'm sure the Pri is unique in that aspect, as i used many grades of octane in my old car with no trouble.