Fuel Grade Used - 986 Forum - The Community for Porsche Boxster & Cayman Owners

RandallNeighbour · 07-17-2005, 01:00 PM

My mechanic told me that premium fuel is truly not required in my boxster. The middle grade offered will be fine. He said the computer will shift a little and it will run the same and do no engine harm.

But, mechanics often say things like this because they don't see the need for the added expense, but don't have lots of long-term personal experience.

I know that probably 99% of the boxster owners on this list use premium at every fill up. No doubt in my mind. But I would like to hear from anyone who's consistently run the middle fuel grade in their boxster for months on end and can tell me it hurt performance, fuel economy, did engine damage, etc.

At the expense of being seen as dogmatic, I don't particularly need posts from premium advocates who feel the need to tell me why to use it and only use it. I too am a premium advocate and don't need the preaching to the choir. I just want to read what users of middle grade fuel have found, and you know who you are... the non-conformists who don't care or actually know better than what the manufacturer recommends.

For most everything I've asked my mechanic, he's told me to follow the factory recommendations for brake fluid, oil weight, etc. But on this one he just blurted it out when I told him I was expecting $2+ a gallon for premium by the time we got to CA next week.

deliriousga · 07-17-2005, 01:40 PM

I tried it for two tanks, one running 87 and one running 89. Since my computer has not been chipped, it does as your mechanic said and adjusts the engine to compensate. And compensate it does. Lost power and fuel economy, especially with the 87. I didn't run it for months on either because the performance difference was not worth $1.50 per fill-up.

Btw, if yours is chipped you most likely cannot do this. The computer has built in compensation as mentioned above and the chips fine-tune the engine to run at peak performance so it can't handle lower octane fuels.

Brucelee · 07-17-2005, 04:30 PM

Your mechanic is a moron. I can't run lowest grade in my wife's Subaru without her noticing that the car has lost power.

I actually wouldn't even try it in any of my Porsches.

RandallNeighbour · 07-17-2005, 07:46 PM

OK, this is good input. Hans isn't a moron overall though... everyone says stupid things from time to time. I just caught him doing it and will avoid the lower grades of fuel.

Thanks for your input! I had a feeling I was right to ignore him, but I wanted it validated and validated it is! I love this forum.

Brucelee · 07-17-2005, 08:44 PM

My apologies to Hans. I spoke too hastily.

SD987 · 07-17-2005, 09:42 PM

I don't know what gas stations are like in the Houston area, but when I lived on the east coast, gas was available in - 87 -89 - 91 -93 (94 for Sun). Now 93-94 is sadly not available on the east coast, 91 is the top. But if 91 is a "middle" grade where you live, perhaps this is what your mechanic OKed. The Box owner's manual states that if 91 is the best you can get, this is just fine and the engine will compensate.

Incidentally, I have heard that 96 grade is available at select 76 stations in the LA area, has anyone found such a station and experimented with this super fuel in their box?

trube78 · 07-17-2005, 10:54 PM

1. If you have performance software you will notice it in HP and MPG. The new software gets some of its gains by decreasing tolerances to allow for a specific octane rating (among other things). Factory software allows for a larger range of octane ratings although engine performance data (HP, torque, and MPG) is taken with higher octane rating i.e. the recommended octane.
2. I tried midgrade vs high test (never considered low test) in a 3.0 Z3 and an MDX and found.
a. In the city negligible gas mileage change about 1/2 MPG. Power may have been decreased but it was not really noticable (IMO). Others say it is but I found it unusual to be pushing the car in the city that I might notice.
b. On the highway, lost about 2 MPG with Midgrade. Power loss was noticable in the mountains but not so much in the flats. Did not compare 0-60 times as that required a good place/way to measure and more than a few runs to get enough data. I even made some identical long trips 300+ miles with both fuels and the results always showed a loss of about 2 MPG.
3. As far as engine damage, your mechanic is right the computer will sense knocking and other problems historically (in older cars) associated with lower grade fuel and compensate. However as I stated above MPG, HP, and Torque will be affected.
4. Finally, for highway driving if you are getting 20 MPG with midgrade and 22 MPG with premium. At current prices (i.e midgrade at about 2.50 per gallon). High test would need to cost over 25 cents per gallon more to make midgrade a financial bargain.
Hope this makes sense.
ATB,
Tom

roman · 07-18-2005, 04:12 AM

Just a correction to a previous reply . . .

I've been using Amoco (BP) for years . . . their gold pump is 93 octane. Shell's high test is also 93. I haven't checked out the rest, but 93 octane is certainly available on the east coast (the Wahington, DC area anyway).

RandallNeighbour · 07-18-2005, 05:43 AM

Quote:

Originally Posted by Brucelee

My apologies to Hans. I spoke too hastily.

On his behalf, your appology is accepted. He'll never know though cause I remember what you posted last week.

What's said on the forum stays on the forum.

Or was that only with spousal discussions?

RandallNeighbour · 07-18-2005, 05:45 AM

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 · 07-18-2005, 06:27 AM

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 · 07-18-2005, 06:52 AM

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

jmabasa · 07-18-2005, 09:18 AM

Quote:

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 · 07-18-2005, 09:32 AM

Quote:

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 · 07-18-2005, 09:43 AM

Quote:

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

ho2go · 07-18-2005, 10:57 AM

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.

Quote:

Originally Posted by Perfectlap

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

Perfectlap · 07-18-2005, 11:09 AM

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

deliriousga · 07-18-2005, 11:48 AM

Quote:

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 · 07-18-2005, 12:01 PM

Sweet, thanks!

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

Quote:

Originally Posted by deliriousga

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

Rail26 · 07-19-2005, 03:03 PM

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.