Fuel grade?

[billiard13]

What's the best grade fuel to use in an Opel that hasn't been converted to unleaded fuel yet? Should I assume the highest grade available?

Thanks,
Claud

[namba209]

My 72 GT owner's manual states low lead or unleaded gasoline of 91 octane is required. HTH.

Ron

[mjewell]

i run 100 low lead aviation fuel in mine, and it loves it. you can find it at an airport. try to find a place that has self serve fueling, and get to know the people that run the fbo. i am a partner in an fbo at new century, kansas, and we have guys that will come in on fridays to get gas for their hot rods. we chat with them, show them our cars, etc. they get good gas (100+ octane) for a lot less than the track sells it for, and we get to talk cars on friday afternoons!!

ps any of you kansas city area opelers feel free to come out for the good gas!!

mike

[pvcar]

about avaition fuel i have access to my local torrance municiapl airport, i have been thinking of filling up one day with a full tank of 100 octane, it cant hurt to try it, it hasnt killed an opel yet, he he he.

[RallyBob]

Run the lowest octane you can without detonation. Higher octane will do nothing but empty your wallet. You will also make more hp with the lowest (safe) octane. Dyno proven....

[GTJIM]

A little realised fact is that lower octane gas actually has more energy per pound than high octane gas. Plus the lower octane gas burns quicker and so needs less ignition advance.
The higher octane fuels reduce the tendency to detonate by being made to burn slower.

In consequence lower octane gas gives more power and better gas milage - as long as detonation does not occur. Just as Rally Bob says.

[mjewell]

my point with using aviation fuel is this:

burning unleaded fuel in an engine designed to use leaded fuel will cause the exhaust valves to eventually burn up. the valve seats in these engines are not hardened, causing them to heat up and erode faster.

aviation fuel contains lead, which does raise the octane, but it also helps cool the exhaust valves & seats.

true, lower octane (unleaded) fuels are cheaper, but just try to find a leaded fuel anywhere. the only place you can still get it is at a ractrack, and it's about $4.50/gallon. aviation fuel is around $2.50/gallon.

[baz]

it's about $4.50/gallon. aviation fuel is around $2.50/gallon.

i wish we were paying that in the uk its $6.47 for unleaded pump gas @ 95ron octane

[BQS4]

Here in Atlanta, GA, where gas is about the cheapest, it's $1.56 a gallon USD

[namba209]

Here's another thing to consider about using AVGAS. It is formulated to be used in aircraft engines that do not turn above 3750 RPM. They figure out the burn rate at the refinery. I found this out in A & P school. Had a friend way back when I was racing bikes, filled his tank with 110-145 octane, he ran like a bandit for about 3-4 laps, then his engine siezed up. He was jetted for the gas, but it didn't help. And he was running above 10,000 RPM.

Ron

[RallyBob]

Originally posted by mjewell but just try to find a leaded fuel anywhere. the only place you can still get it is at a ractrack,

True...but the reason is it's illegal to operate a motor vehicle on leaded fuel on US highways these days, courtesy of the EPA.
Aviation fuel has an added benefit too, it runs very cool EGT's. A friend of mine used to run it in his Opel racecar, mostly because of the cost. But we found the car ran about 10 degrees cooler water temps and about 200 degree cooler EGT's than with 'real' racing fuel.

Another problem in some states is that AV gas can't be sold to non-pilots (that is, to car guys). Here in Connecticut we have our own Department of Environmental Protection (DEP) which is tougher than the EPA. They have made if very difficult to circumvent a lot of these loopholes. Of course, I can drive 1/2 hour north to Massachusetts and they'll not only sell me AV gas, they'll pump it into my gas tank!

[tuckeroo85]

i buy regular unleaded and use a lead substitute addition in the tank. it seems to work fine. have not had any problems yet.

kevin

[bq97]

The REAL reason it is illegal to use aviation fuel in a motor vehicle is not the lead/EPA issue but the federal and state highway taxes we pay on the fuel we buy at the pumps. You can get "Farm Only" fuel which depending on locality can be 60 cents a gallon cheaper then the same grade/type highway fuel. The only difference is the tax issue and the dye used to distinguish the two.

Brian

[cherokee]

"The REAL reason it is illegal to use aviation fuel in a motor vehicle is not the lead/EPA issue but the federal and state highway taxes we pay on the fuel we buy at the pumps"

BINGO.

[bosco]

would 87 octane run cleaner than 91 octane......in an emissions test environment?

[jeff denton]

I think we should go into an explanation of how octane rating and ignition timing go hand in hand. And how ignition timing can affect horsepower.
You ever hear anybody say they switched from low octane to high and the car ran better? I call bull unless they advanced their timing.

[bosco]

timing is about 5 degree advanced.....given it doesn't ping with the regular grade will it be burning cleaner than with premium?

[GTJIM]

Originally Posted by bosco would 87 octane run cleaner than 91 octane......in an emissions test environment?

Not if the slightest amount of detionation begins to occur - and retarding the spart to prevent that will push the emissions up through the roof!

[jeff denton]

As far as the Opels are concerned, we have to keep in mind the "high" compression ones and the "low" compression ones, let's not get anyone confused and cause a mistake (holes in pistons, etc.).
Compression ratio, ignition timing, octane rating. Three factors to fully understand before playing with gas and timing...

[kwilford]

Originally Posted by GTJIM Not if the slightest amount of detonation begins to occur - and retarding the spark to prevent that will push the emissions up through the roof!

Emissions testing generally measures three things; Nitrides of Oxygen (NOX), Unburned hydrocarbons (HC's) and Carbon Monoxide (CO). All other things equal (in the absence of detonation, more about that in a moment), NOX goes UP with more advanced ignition, due to higher combustion temperatures, if I recall the basic engine theory that they tried to jam into my head in "Internal Combustion Engines: Theory and Practise" during a very hectic third year of Engineering. Unburned HC's go the other way, while CO has more to due with mixture. The curves relating to HC/NOS and CO are all a bit contrary to each other wrt to mixture, which is why three way catalysts and lambda-sonde O2 sensors with highly accurate fuel mixture feedback control is the norm is modern fuel systems. Well, they ALL are more affected by mixture, but let's stick with the issue of octane and ignition advance.

Octane is a measurement of the TEMPERATURE that gasoline will spontaneously (prematurely) combust. What goes along with that is also the HEAT of combustion, and the SPEED of the flame propagation. Higher octane fuel generally has a higher heat of combustion (more long chain HC molecules which have a greater specific heat when burned) but I believe that the flame speed is actually LOWER at higher octanes. Heady stuff! But in simple terms, if you aren't pinging (detonating) on regular gas, and your ignition is sufficiently advanced to get optimal thermal conversion (35 degrees at maximum advance), then higher (or lower) octane fuel will provide little significant benefit, regarding either power or emissions. Actually, clean crankcase oil has more benefit. Less off-gassing due to accumulated unburned HC's.

HTH

[oldopelguy]

One thing not mentioned so far is the fuel consumption with the different octane fuels. In my wagon, running a tank of 87 with lead substitute usually yields @24mpg. With no other adjustments, running 93 octane and the same lead substitute usually yields closer to 27mpg. My jeep is the same way. Since the car doesn't run markedly better either way, what I usually do is compare the dollarage of the fuel when I get ready to pump, ie how many dollars will it cost me to go 200 miles at 87 octane times its price vs. 93 times its price. That's my biggest factor in choosing.

FWIW, I haven't been able to justify premium based on cost with anything more than a few cents difference in price, and at today's prices I just burn the cheap stuff. I still get it once in a while, but not for any particular reason.

[kwilford]

Originally Posted by oldopelguy One thing not mentioned so far is the fuel consumption with the different octane fuels. In my wagon, running a tank of 87 with lead substitute usually yields @24mpg. With no other adjustments, running 93 octane and the same lead substitute usually yields closer to 27mpg. My jeep is the same way. Since the car doesn't run markedly better either way, what I usually do is compare the dollarage of the fuel when I get ready to pump, ie how many dollars will it cost me to go 200 miles at 87 octane times its price vs. 93 times its price. That's my biggest factor in choosing. FWIW, I haven't been able to justify premium based on cost with anything more than a few cents difference in price, and at today's prices I just burn the cheap stuff. I still get it once in a while, but not for any particular reason.

Makes sense, since the higher octane gas has more energy (greater specific heat), but usually you have to advance the timing to get the full advantage. Up here, Premium is about 10 cents per litre more than Regular, which is about 80 cents per litre. So that is about 12.5 % more, which is EXACTLY your increase in mileage. I have read that mileage with Premium might be as much as 10% more, so your result is better than most. And at 10% more mileage and 12.5% more cost, it just doesn't make sense, unless you want the additional HP associated with the advanced timing that you MIGHT be able to accommodate with Premium.

[Wolf Spyder]

What are some good lead substitutes that can ge found here in the U.S.?

[Sparky73]

This may be kind of a simple question but just to get to the point for some people, what is the best fuel to run in a stock Opel engine?

I have a 1973 Opel..should I put in Unleaded Reg, Plus, or Premium. Jared says that he just puts in Plus and it works just fine. With Premium, should I still add a Lead additive, or would I be fine not using it with the Year of engine I got.

Thanks in Advance,
Jon Samuel

[jordan]

the lead additive and octane are not related as far as I know. The prefered octane will be specific per engine (high compression vs low compression) ignition system ect. The lead additive is needed if you dont have hardened valve seats, if you haven't been using it the damage has already been done and it makes no sense to use it now.