110 octane safe?

[HellRaiser92]

I was talking with a friend of mine today and he seems to think that putting 110 octane wont hurt a car that doesn't need it. He mentioned how he needed some for his car.

He said it isn't good for lawn mowers but it doesn't hurt cars at all. So I said well then if I put some in my little 4 banger it won't hurt it? I thought motors with low compression were not supposed to have such high octane levels of gas. And oh yeah what does happen if you put really high octane fuel in cars that don't need it?

[PKRWUD]

Your friend needs to go back to school. Octane is what slows down a gasolines burn rate. Higher octane = slower burn. For optimum performance, you should use the LOWEST octane you can operate safely with. In otherwords, if it doesn't ever ping or detonate with 91 octane, try using 89. If it still doesn't ping, try 87. If it still never pings, you're good to go. The ONLY reason to use a higher octane gasoline is because you have modified the engine to the point where your current octane allows pinging under adverse conditions. Advancing the timing and increasing the compression both usually require the use of a higher than normal octane, but you still should use as low an octane as possible. High octane gasoline has a false reputation of increasing power by itself. This is not only false, but it will actually slow you down. Gasoline companies give their high octane grade names like "High Performance" to increase sales. The truth is that fast cars use high octane gas, but it's the engine mods that require the high octane, and that make the car fast, not the high octane gas itself.

Will 110 octane gas hurt your engine? Not really, but unless your engine is very modified, it will slow it down, and it will eventually leave unburned deposits.

Tell your friend to just leave his emergency brake lightly applied instead. It will have the same effect on performance, and save him a ton of money.

Take care,
-Chris

[1BAD89]

I thought motors with low compression were not supposed to have such high octane levels of gas.

They don't need it. It's a waste of money on low compresion motors. At almost $5 a gallon, it's some high dollar stuff. I have to run mostly 110 in my truck, otherwise it will knock pretty bad. Also strictly 110 will destroy your oxygen sensors.

[elmir50]

One of the most misunderstood things about fuels is the relationship between octane and burn rate.

Octane is simply the fuels abilty to resist detonation.

Burn rate is NOT related to the octane number.

All the pump gases that you buy at the gas staion will have approximately the same burn rate.

One thing with pump gas is chemists add what they call "low end volatiles". Low end volatiles aid in cold engine temp performance and starting your engine when it is cold. Race gases don't contain low end volatiles. These low end volatiles ignite at lower temps, they aid to create heat to set off the rest of the charge when the engine is cold.

So, if you tried using 110 octane race gas, your engine would be very hard to start and would perform very poorly when cold, this is assuming the 110 has the same burn rate as the regular pump gas.

As far as fuel requirement for low or high compression motors. Their are more variables to consider then I care to mention.

Just cause the static compression is low that doesn't mean squat. What are the actual cylinder pressures when the engine is running??? Maybe it's runnig a ton of artificial boost.

And now how about if the static compression is high, with alot of valve overlap, cylinder pressures will not be so great while the engine is running. This is an extreme example but it should show you that alot depends on the dynamics of the engine.

[PKRWUD]

Originally posted by elmir50
One of the most misunderstood things about fuels is the relationship between octane and burn rate.

Octane is simply the fuels abilty to resist detonation.

Burn rate is NOT related to the octane number.

Interesting. I was taught that octane and burn rate go hand in hand.

[Road Rage]

I do this for a living, and agree with the other posters abut the uselessness of adding octane to get more power in a car not designed for it.

Two other things worth mentioning:

1) Race gas, and especially AVgas, usually do not contain the fuel additives needed for longevity on the street, including detergent additives
2) When the octane rating greatly exceeds the requirements of the engine, the slower burn rate means that often the fuel is still buring as the exhaust valve opens, which can lead over the long haul to reduced exhaust valve service life. Just as bad, the unburnt fuel usually ends up in the first catalytic converter, where it can damage or melt the honeycomb.

Not recommended.

[mustangman65_79]

hmmmmmmmmm, Now I think I'm more lost then before???

[mustangman65_79]

I read it again, but who is right-who is right???

[elmir50]

There's lots of literature out there on fuels, just look.

I am a little puzzled by your reply Road Rage....are you a chemist?
In your response you are associating octane and burn rate to be the same when in fact they are different. Your other 2 points are well taken.

When determining burn rate, you use a distillation curve. This curve represents the amount of gas that evaporates for every 10 degree increase in temperature, until the fuel is all gone.

Books I have sourced my information from include, magazine articles and technical books. Nitrous Oxide book and a Smokey Yunick book.

[1969Mach1]

Wow that is interesting stuff. You learn something new everyday. I never quite new that was how it works.

Thanks for the indirect knowledge.
§am.