Can someone explain the whole higher octane gas is not better thing?

95Vert · Jul 22, 2006

I know someone said this wasn't true but I don't remember the reasoning behind it. I know that when I switched back down to regular from 93, my car felt "better". And I know it wasn't just my head.

illwood · Jul 22, 2006

Octane # is essentially a resistance to igniting. So a higher octane is harder to ignite than a lower octane #. High compression engines use higher octane because if they didn't, the fuel would ignite on the compression stroke before the spark plug created a spark and the engine would knock.

If you run high octane in an engine that doesn't need it as knock prevention, then you would suffer lower power from the fuel being harder to ignite.

95Vert · Jul 22, 2006

thanks matt, now I have to explain that to my parents since they're running 93 oct on their 05 grand am and 02 sport trac.

1slow95 · Jul 22, 2006

Some places put additives the higher octane gas to help keep the engine cleaner. Other than that, if their cars are not pinging then there's no reasone to run higher octane in those cars.

95Vert · Jul 22, 2006

So when would it be appropriate to run a higher octane?

illwood · Jul 22, 2006

On a stock car, the owner's manual will tell you which octane is recommended.

When you start modifying the car, like higher compression and or a more aggressive timing curve, you then need to run a higher octane to prevent detonation.

1slow95 · Jul 22, 2006

illwood said:
On a stock car, the owner's manual will tell you which octane is recommended.

When you start modifying the car, like higher compression and or a more aggressive timing curve, you then need to run a higher octane to prevent detonation.

:Word:

Pokageek · Jul 22, 2006

Right on. Higher octane doesn't mean your car will be faster with it lol. Higher octane just means it is less "explosive." Right gas for the right car.

95Vert · Jul 22, 2006

My parents don't think they'll go faster but they think that it's cleaner and will help them get better gas mileage.

Pokageek · Jul 22, 2006

Interesting. The whole cleaner thing was shot down years ago by congress. One of the gas companies were claiming that there gas was cleaner by directing your attention to a clear glass window in the handle of the pump - Amaco I think. That advertising was banned because they rules out the possibility of one gas being cleaner than another as false advertising. If you want your car to run cleaner, put some additive in it from Pep boys to clean the injectors. You would think that if the 93 is less combustable then the car won't run as well with 93 if it is supossed to have 87. Wouldn't that result is lower efficiency and worse gas mileage? Any chemical engineers want to comment?

HISSIN50 · Jul 22, 2006

Some folks do notice slightly higher milage with higher octane. I also wonder if a bit has to do with the additives that Mike mentioned.

Nacho, if you're not pinging now (on lower grade fuel) and you didnt change timing, you very likely DID improve performance.

To answer your question another way, another time to up the octane is when one sees pinging and cant back timing down anymore. At that point, higher octane can be appropriate.

Your parents cars' likely have knock sensors, which kinda adjusts for fuel grade anyhow (to an extent).

Good luck.

95Vert · Jul 22, 2006

Thanks guys. I just wanted to have an explanation to give them when they ask me WHY?

Blackened302 · Jul 22, 2006

so if you bump the timing up, to say 14*, which octane should you run?

mo_dingo · Jul 22, 2006

Punisher302 said:
so if you bump the timing up, to say 14*, which octane should you run?

87. if it pings, back the timing down. Running higher octane just to have a more agressive timing curve is like putting a humidifier and a de-humidifier in the same room and letting them battle it out. Very counter-productive.

95five-oh · Jul 22, 2006

not trying to steal the thread, but my car is bone stock with 150k on the odometer and the timing has not been fooled with to my knowledge, but if i run anything but 93 octane, it pings and knocks like a diesel...anyone know what would cause this?

bill302 · Jul 22, 2006

95five-oh said:
not trying to steal the thread, but my car is bone stock with 150k on the odometer and the timing has not been fooled with to my knowledge, but if i run anything but 93 octane, it pings and knocks like a diesel...anyone know what would cause this?

1st thing to do would be to check the timing and repost results...and go from there..

mo_dingo · Jul 22, 2006

95five-oh said:
not trying to steal the thread, but my car is bone stock with 150k on the odometer and the timing has not been fooled with to my knowledge, but if i run anything but 93 octane, it pings and knocks like a diesel...anyone know what would cause this?

Yup, as bill said, check your base timing with the spout out. It could have been bumped. Also check your balancer for rubber degredation as this will make your timing light useless.

But a search on this forum for "pinging" will bring a multitude of solutions and the implimentations of these fixes, first and foremost being cleaning the MAF/IAT and checking the ECT's proper operation.
Scott

69clark · Jul 22, 2006

Also usually a lower octane fuel is a faster burning fuel, know as fast burn. Race gas has a lower burn rate, however some race gas is formulated to be a faster burn than others. So if that is confusing than just remember that pump gas usually has a faster burn rate than av gas or race fuels.

69clark · Jul 22, 2006

One more note, usually this is why it is very important when selecting fuels or building an engine, you must build the engine around what fuel you will be using to make the most power. This isn't neccessarily as important for street cars running on pump gas as it is for purpose built race engines.

nmcgrawj · Jul 23, 2006

mo_dingo said:
87. if it pings, back the timing down. Running higher octane just to have a more agressive timing curve is like putting a humidifier and a de-humidifier in the same room and letting them battle it out. Very counter-productive.

So are u saying that you wont see any improvement when bumping the timing and running 93 to eliminate chances of pinging?

Can someone explain the whole higher octane gas is not better thing?

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