Low octane fuel for a 2,000 mile road trip to Phoenix

[ejmc11]

Hi folks,

I'm loading up my 2007 S tomorrow and moving out to Phoenix -- a good 2,000+ mile trip. In the interest of saving a bit of cash during the trip, I was thinking I could just put in some lower octane fuel throughout as I won't be doing any high revving with the car for the trip. Once I get to Phoenix I'll run the car super low on the low octane fuel, then go back to using 92+, so I should be rid of most of the bad stuff when I'll want to properly enjoy the car's performance again. Anyone have any compelling reasons to share to NOT do this ?


P.S. If anyone's in Phoenix, please drop me a line, would be nice to meet up, as I only know 2 other people out there at the moment!


Cheers,

Emmanuel

[unklekraker]

Originally Posted by ejmc11

Hi folks,

Once I get to Phoenix I'll run the car super low on the low octane fuel, so I should be rid of most of the bad stuff when I'll want to properly enjoy the car's performance again. Anyone have any compelling reasons to share to NOT do this ?

you already said yourself that it's a bad stuff, so why still put it

*my own experience*
It happen to my Suburban, use different brand (long interstate drive from CA. to Seattle) and low octane....I saved $0.20 per gallon but I end up changing my fuel filter after I got back

[Cloudsurfer]

Very poor idea, IMO. Just because you won't be doing any high RPM, spirited driving, these are still high compression, modern performance motors. The knock control in the DME will retard ignition timing to compensate for the lower octane fuel, and should save you from motor damage. However, you will have reduced the performance of the motor for a good bit of time, even after you have re-fueled with higher octane fuel until the DME starts to introduce more spark advance once it hasn't had any knock from the lower octane fuel. Hypothetically, a DME reset should start the clock over and force the engine to "re-learn" how to run on the proper fuel.

At the end of the day, how much are you going to save? Lets say you average 20MPG over 2000 miles, you're going to burn 100 gallons of fuel. Say you save $.25 per gallon, you just saved $25. If you average 25MPG (more likely in a highway cruise in your car), the savings are even less.

To me the risk is nowhere near savings that small. The motor was designed to burn Premium Unleaded, and thats all I'd put into it.

Patrick

You'll be using about 80 gallons. Where I am, premium is about .10 more and possibly .20 at some places. That's~ 8-16 bucks total difference on your trip.

The box has a knock sensor, however I'm guessing at least one knock must be detected before it backs timing out, therefore, there is some theoretical damage from the one ping. Also, I have no idea how long the DME takes to re-adjust maps.


Given the long trip, there may be sections where you might want to get on it, or you unexpectedly hit a hill while you're loafing around in low rpm's with a drink in your right hand (if you have a manual tranny).


That said, It's a coin flip for saving $8-16 bucks. IMO, if it were me, it's not worth it because I like knowing I can wind it out whenever I want

[SD987]

I think your idea is fine. Depending on the route you take, you'll be going through some pretty high altitudes where the less dense air deters knock. Furthermore, in several western states (most notably California, where Porsche sells the most cars) 91 is the highest octane you can purchase. Our cars run fine on 91 24-7.

[trube78]

On several occassions, I was forced to use regular (low octane) gas on a few highway trips in other high performance, 91/93 Octane recommended vehicles, when high test was not available. Although not a strict scientific test I always seemed to lose 2 - 4 MPG with the lower octane. Since the engine and DME were designed to run with high octane I suspect you operate outside the design parameters and thus less efficiently. Maybe if you ran it long enough the DME would fully adjust to the lower octane and your mileage would improve but maybe not. Since the MPG loss is about 10% of normal the cost savings from low test to high test would need to be about 10% for you to break even. So ... there would not be any immediate $$$ savings.

The anti-knock sensor should protect the engine from damage due to knocking unless you were attempting to drive at or near full throttle and pushing redline during acceleration. But I believe you would see more savings by using your cruise control and avoiding hard acceleration to pass or get up to speed. Driving at the speed limit and using cruise would probably be more effective at improving MPG and thus saving more money than using low test fuel.

ATB,
Tom

[Brucelee]

Saving $10 is that important?

[ejmc11]

Originally Posted by Brucelee

Saving $10 is that important?

I've got to be able to afford these payments somehow.. it's been 4 days since I've eaten anything, that last packet of ramen noodles really filled me up.

Just kidding of course.. you guys make some good points, thanks for all the thoughtful replies. I'm going to stick to premium after all, the car's made me smile so much from the last 3 weeks I've had her, might as well give some love back!