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

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!

[FrayAdjacent]

Probably not a HORRIBLE idea, yet not a GREAT idea either.

You might try to save a buck or two by using MID GRADE. The idiots at the dealer I bought my Box from put $20 worth of mid grade in it. It ran fine, but ran noticeably better when I filled up with premium.


BTW, I drove 1000 miles to Phoenix and then back a little over a month ago. I averaged 31mpg for the whole trip!

[markab986]

old link...not saying this is the fuel gospel, but good points

http://www.straightdope.com/columns/041008.html

[dmenn]

You probably paid at least $50K for a brand new Porsche - and you're worried about saving 20 cents a gallon on gas? The least you can do is put the right gas into it. Buying the car is one thing, actually driving and maintaining it is another thing, and can be quite pricey.

[Cloudsurfer]

Just as an aside, higher altitude, less dense air does not deter knock, but increases its likelihood. This is a phenomenon known as "density altitude" in aviation, and it has to do with reduced aircraft (and thus for us car guys, engine) performance due to high humidity, high temperature, high altitude- all of which cause lower air density and reduced performance.

Patrick