[oldopelguy]

dollarage

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]

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.

 

[greensmurf20]

my GT gets about 20MPG with regualr grade fuel, 26 with midgrade, and 26 with premium. so i just run midgrade, as i get the most miles per dollar of fuel.

 

[Sparky73]

Well my problem is, I have never even had my engine the least bit torn apart, nor do I know what the previous owner put in for gasoline. The few times that I have put gas in just to try to get it started..it was just plain old Regular unleaded. Seemed to run fine.. Once I start driving and such, I am probably going with a higher grade though. I have heard that some of the newer model GT's were already switched to take unleaded because it was around the time that laws were being changed..

 

[Wolf Spyder]

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.

What could bew the expected damage?

 

[Crusher]

octane

As mentioned by Kwilfor in an earlier tread...
The reason for using High Octane is because low octane fuel burns too fast...lets say the fuel is completely burned when the piston gets half way down...thats power lost...half the piston travel is wasted ( Low Octane ).
You need to get the fuel to burn slower (higher octane) so it will burn further down the cyclinder which also increases the efficiency and actually lowers the initial detonation pressures in the cyclinder which makes for a smoother burn.

 

[rockytopmark]

No sure answer?

I have read many comments saying to "keep in mind compressions of motors when selecting fuel," but I don't see a glaring "correct" choice for either compression. I do summize, though possibly inaccurately, that higher octane may be better overall, but do not see which octane is better for Low comp and which for high comp. Please clarify if possible.

Thanks, Mark

 

[bear]

Mark, there's no hard fast way to tell what the octane requirement is for each engine, there are just too many variables. Location, being one of them, engine mods, ignition, exhaust system, ad infinitum. The best way, and this is an oldie, but goody, is to set the ignition as close to optimum as you can, find a fair steep hill and floor the gas pedal going up the hill in as high a gear as you can, with the highest octane gas number you can find. If the engine pings, retard the timing until it doesn't ping. Run that gas out of the tank and do the whole mess again with the next lowest grade octane. Then do it again with the lowest octane gas you can get. If during this trail and error process, you cannot get the engine to quit pinging, you have to go the the next higher octane gas cause that's the minimum octane your car requires. Or you can read what's in the Owner's Manual for the year car and just go with that. HTH.

 

[jordan]

I always use the highest octane I can find though if it doesnt ping with 93 there is no sence getting 105. Basically if I have a choice between regular and the difference in the 2 premiums are under $.10 difference I'll go with the highest, better safe than sorry.

 

[OrangPeEL]

correct pump octane rating & why

… I don't see a glaring "correct" choice for either compression… which octane is better for Low comp and which for high comp. Please clarify if possible.

Thanks, Mark

Assuming you just seek glaring answer of “real world” practicality on which of three pumps you should pick. The minimum required octane rating, established by OEM testing on their stock engine, is likely correct for that engine. When we modify an engine, the correct minimum octane rating required may change. The correct octane rating of fuel to use is: the one that’s high enough that it doesn’t cause engine to knock.

To possibly clarify… advance sorry if this becomes TMI -

An octane rating is a comparison of that blends spontaneous combustion point… to the known spontaneous combustion point of a true octane% blend fuel. A 92 octane rated fuel “could” contain 0% octane and still spontaneously combust at same level of compression as a fuel containing 92% octane + 8% heptane … & is why it’s possible to have an octane rating higher than 100 (it’s simply a spontaneous combustion point higher than that of 100% octane)!

Higher comp. ratio (of same disp.) engines pack the same volume of air/fuel into a smaller area. From this tighter packed/same quantity of fuel, when efficiently and timely burned, comes potential of greater transferable power. This is obviously the desirable combination.

With either high or low compression engines, what you want to avoid is knocking… when fuel combusts before piston stroke is ready to use it… bad for engine parts! This can happen spontaneously under compression (before the spark plug lights off). Fuel mix becomes more volatile the greater it is compressed… higher octane rated fuel can be compressed more before it spontaneously combusts. You will pay extra for this feature at pump.

A lower compression engine will burn higher octane pump grades just fine- but lacks the proper timing and mechanical advantage to transfer those extra octane points into more power. So, when I run premium (92 octane rated) in my stock low-comp ’73 (and I admit I sometimes do ‘cause it makes me feel good ), I’m throwing away the extra octane points I’ve purchased at the pump.

-Dan

 

[jeff denton]

Has anyone here ever played with oxygenated fuels? Some of the racing gas suppliers' websites have numerous choices, very confusing, but one I found claims up to 15% more power in an engine at 11:1 compression ratio.
Since our rules forbid oxygenated fuel, it must be beneficial, but I want to know why and how to use it properly. Perhaps some of our geniuses here can help me understand how this works.
Not that I would ever break a rule, of course. I just prefer to disregard ALL of them, anything to kick ass. It's just for fun, remember. The four year old Compact Class track record was recently bettered by three one-hundredths of a second. Was awarded without inspection or teardown. Next week the same car broke his own record by three TENTHS!
It hit the fan in the pits. How does he do it?
We know how. Tech man does too, but doesn't care. It's just for fun. I wanna play, too! Like, in a couple weeks.

 

[bear]

Jeff, all the gas here in SoCal is oxygenated as mandated by the CARB folks. It's supposed to help cut down on pollution. Whether it helps as far as performance I can't say. I sure haven't noted any difference in the monza using it. One thing I will say about it. It caused an engine fire in my El Dorado motorhome when the fuel ate through the fuel line and did the same on numerous other cars as well, and most of those were VWs. It was not uncommon to see 3-4 cars a day on the side of the road with evidence of a fire, when it first came out. So if anyone choses to use oxygenated gas, change the rubber fuel lines first. :yup:

 

[RallyBob]

Has anyone here ever played with oxygenated fuels? Some of the racing gas suppliers' websites have numerous choices, very confusing, but one I found claims up to 15% more power in an engine at 11:1 compression ratio.
Since our rules forbid oxygenated fuel, it must be beneficial, but I want to know why and how to use it properly. Perhaps some of our geniuses here can help me understand how this works.

As you know, the basic rule for making power is: Add more oxygen. Then add more fuel until A/F ratio is correct. So if you have a restricted engine that can only breathe in 'so much' air for one reason or another, adding oxygenated fuel allows you to increase the amount of oxygen in the engine for a given port size/cam size/carburetor size. You just richen the fuel mixture so that you don't run lean (like adding nitrous kind of).

When they used to change over CT fuels in the winter time to reduce emissions, they used an oxygenated fuel with MTBE. I had to increase my jetting by two jet sizes to compensate every fall, than lean the mixture again in the spring.

 

[Bill Hoffmann]

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

Ron

I realize I'm responding to a post from 2004, but yes, the sticker inside the glove box of my '74 Manta states the following:

"This vehicle is designed to operate on unleaded or low-lead fuels of at least 91 Research Octane. ...The engine does not require premium fuel. Therefore, its use would be and unnecessary additional expense."

This is seemingly a contradiction since I would consider 91 to be premimum in some markets, but if you notice on the pump, the octane rating is an average of Research and Motor octane, (R+M)/2 method. Therefore, you are not comparing apples to apples. In my experience, the low compression engine even with timing somewhat advanced from the factory setting will run on the lowest octane pump gas (86 or 87) with no knocking. However, the high compression (pre-71) engines probably require the mid grade (89 or so).

Using a higher octane than required will only be a benefit in newer high compression engines that can adapt to allow maximum spark advance before detonation occurs. It's surprising how high the compression is on some of these new cars through the wonders of modern engine management. Even my Saab 2.0 turbo will run on 87 octane without knocking, but I believe I would see an improvement in performance if I ran premium in it.

As far as oxygenated fuels are concerned, this got me in trouble a few years ago. I drive quite a bit, and I habitually reset my trip odometer when I fill up so that I can easily calculate my mileage as well as how many miles I have untill I need to refill. On my company Taurus when I lived in Chicago, I would routinely get 400 miles to a tankfull. All of a sudden I started running out of gas with only 300 miles on the odometer. This sounds stupid, but it happened several times and I have the extra plastic gas cans to prove it. I finally figured out they had switched to oxygenated fuel in Chicago. Now I try to fill up in rural Wisconsin, Illinois or Indiana if possible, since I know the price will be lower and my mileage will increase significantly. My question is, is there truly an environmental benefit if my mileage decreases 25% when using oxygenated fuel?

 

[CoriolisSTORM]

Offtopic but interesting nontheless, I saw a spec tag on a Willys MB the other day on another website I frequent and MINIMUM octane was somewhere around 61! Not sure if it ran on leaded or not, never heard it brought up with the old L and F head engines.

 

[jeff denton]

I just went through the VP racing fuel website, they show a lot of oxygenated racing fuels, and describe what applications each works best for. I chose one called CMP. They proclaim to give a more realistic three to five percent increase in power, and predict the carb to need the same percentage in jetting to the richer... makes sense.
They don't warn of any corrosive danger.
But just think. Three to five percent more power. That's easily five horsepower, maybe almost ten, in my perfectly stock and legal :haha: little 1.9.
Apparently this fuel has a very long shelf life, as it is not really comparable to pump gas in some chemical properties, according to a report I just read.
And in another forum, about weapons and destruction (amazing what pops up on Google) a backyard chemist/terrorist says you can distill it into a really nice nerve agent... gonna have to get some now!
I'll bet it's really expensive. I'll call the distributor and find out. Any guesses how much per gallon? I say fifteen dollars, easy.

 

[RallyBob]

I'll bet it's really expensive. I'll call the distributor and find out. Any guesses how much per gallon? I say fifteen dollars, easy.

These days? About $8 to $10 per gallon depending on your dealer.