Fuel Grade Used

[RandallNeighbour]

In Houston, our fuels are usually 87, 89, and 91 or 92... but you've all got me thinking and I'm going to start checking every time I fill up. I'll put in 91 if I can find it and see if it runs the same.

[deliriousga]

If the highest available in your area is 92 octane then you probably won't notice much difference between 91 and 92, but you're still only talking a difference of $1.70/tank if it's empty.

With the different availability of grades of gasoline, they have to make the Porsches run on any octane fuel. Running and running well are two different things, though.

The biggest performance killer with the lower octane fuels is the knock sensor. Its' job is to help save the engine from being damaged by knocking in the cylinders. The lower octane fuel is more volatile so it explodes too early from compression and not from the spark causing the knock. The knock sensor feels knocking occurring and the O2 sensor notices left over fuel going down the cats. The computer starts changing fuel/air mix, timing, etc. to make the fuel combust when the spark occurs and to make sure all of the fuel in the chamber is burned. That kills your performance because the engine was designed to run best with the higher octane fuel.

A lot of people hate the knock sensor because of the retarding of performance it can cause, but I love it. Imagine all of the pressure put on the cylinder when it's on the way up and the gas explodes early putting all of that force down on the piston before it is supposed to. It's kind of like trying to throw your car in reverse while you are still moving forward.

The next time you're in GA head over to Road Atlanta. They have gas stations around there with 104 octane fuels.

[Perfectlap]

Chevron, Texaco, Sunoco: the only stations that don't buy imported crude oil from the the middle east.

[ho2go]

Pardon my ignorance but does this mean better performance? Or was that just a patriotic FYI? (I'm not at all being rude, I'm completely serious... I'll be moving to the US soon and any info on the fuel quality at various gas stations would be appreciated!) Thanks.

Originally Posted by Perfectlap

Chevron, Texaco, Sunoco: the only stations that don't buy imported crude oil from the the middle east.

[Perfectlap]

buying domestic oil is good for competition.
Dependence on foreign oil is making life very expensive nowadays.

[deliriousga]

Originally Posted by ho2go

Pardon my ignorance but does this mean better performance? Or was that just a patriotic FYI? (I'm not at all being rude, I'm completely serious... I'll be moving to the US soon and any info on the fuel quality at various gas stations would be appreciated!) Thanks.

What Perfectlap said AND Chevron with Techron is the best at keeping your fuel injectors and system clean.

[ho2go]

Sweet, thanks!

Sorry for taking this thread off-topic... Please continue discussing mid- vs. high-octane gas, knock sensors, etc.

Originally Posted by deliriousga

What Perfectlap said AND Chevron with Techron is the best at keeping your fuel injectors and system clean.

[Rail26]

HO2GO...Welcome to the US eh?! I have been in Toronto on business for the last month and love it! Both sides of the border have great things to offer!

By the way, I have had good luck with Chevron/Techron. If it is good enough for those cartoon cars it is good enough for me right?

Perfect lap...well said. Reliance on foreign oil has become very costly. As soon as they put out a hybrid Porsche with the same performance, I will be the first in line! I heard rumors of a hybrid Cayenne...don't really want one of those, but would love to stick it to the middle east again.

[jmabasa]

Originally Posted by deliriousga

The biggest performance killer with the lower octane fuels is the knock sensor. Its' job is to help save the engine from being damaged by knocking in the cylinders. The lower octane fuel is more volatile so it explodes too early from compression and not from the spark causing the knock. The knock sensor feels knocking occurring and the O2 sensor notices left over fuel going down the cats. The computer starts changing fuel/air mix, timing, etc. to make the fuel combust when the spark occurs and to make sure all of the fuel in the chamber is burned. That kills your performance because the engine was designed to run best with the higher octane fuel.

A lot of people hate the knock sensor because of the retarding of performance it can cause, but I love it.

Can the knock sensor get damaged in any way? What happens when the knock sensor is damaged?

[RandallNeighbour]

Originally Posted by jmabasa

Can the knock sensor get damaged in any way? What happens when the knock sensor is damaged?

Why it can no longer say "knock knock, who's there?"

[deliriousga]

Originally Posted by jmabasa

Can the knock sensor get damaged in any way? What happens when the knock sensor is damaged?

Yes it can wear out along with all of the other sensors. The knock sensor feels physical movement in the engine. It has an allowable amount of normal movement that won't affect it since the engine normally vibrates. If a cylinder knocks, the engine jumps and the knock sensor feels it. That's when it starts to compensate and keep the knock from happening.

If the sensor wears out or gets damaged and stops working, it will not adjust for knocking. The engine will be allowed to knock. If the damaged sensor takes in bad readings, it can tell the computer to change the mix and timing to a point where the engine runs rough or not at all.

The problem is almost any sensor can do the same adjustments. The sensors are constantly adjusting, several time per second. Every reading they take is instantly compared to other sensor readings and translated into adjustment. It's pretty amazing to see it work, but it also doesn't take much to mess everything up.

FYI: If you want to avoid future headaches, replace your O2 sensors at 100K miles if they make it that long. That's the expected life of the latest type of O2 sensor.

Here are some good articles on sensor diagnosis http://www.autotap.com/obdii_library.asp