Is there a REAL need to use premium fuel?
05-13-2008, 05:02 PM
#32
Fear the Miata!
Join Date: Jul 2004
Location: Chicago
Posts: 20,146
Likes: 0
Received 0 Likes
on
0 Posts
westcoast are you for real? of course i know what a dollar is....been self employed making money for
over 13 years now....what i have learned is that you have to prioritze everything....if 20 bucks is a lot of money for you, then maybe you should be driving a buick
05-13-2008, 05:17 PM
#33
AudiWorld Super User
Join Date: Dec 2003
Posts: 7,152
Likes: 0
Received 0 Likes
on
0 Posts
You're assuming the mileage will be the same with both fuels...
But if the ignition is retarded with 87 then it won't be the same. It will be lower.
I love how people start worrying about this as the price of fuel goes up. Yet the spread between 87 and 93 in absolute terms stays the same. In percentage terms, the spread is actually falling as the price rises. What that means is that the higher octane fuel has to increase mileage by a smaller and smaller amount to justify using it. This is exactly the opposite of the subjective feeling that most people have. When fuel is $1/gal they don't care about paying 20 cents more for higher octane. When fuel is $4/gal. they moan about the 20 cent difference.
As the price of fuel goes up and up, I'm more and more likely to stick with the higher octane fuel on a turbocharged car.
Stephen
I love how people start worrying about this as the price of fuel goes up. Yet the spread between 87 and 93 in absolute terms stays the same. In percentage terms, the spread is actually falling as the price rises. What that means is that the higher octane fuel has to increase mileage by a smaller and smaller amount to justify using it. This is exactly the opposite of the subjective feeling that most people have. When fuel is $1/gal they don't care about paying 20 cents more for higher octane. When fuel is $4/gal. they moan about the 20 cent difference.
As the price of fuel goes up and up, I'm more and more likely to stick with the higher octane fuel on a turbocharged car.
Stephen
05-14-2008, 05:25 AM
#36
AudiWorld Member
Join Date: Dec 2007
Posts: 523
Likes: 0
Received 0 Likes
on
0 Posts
Is it worth risking damage for less than $4.00 a tank?
I personally wouldn't take the chance. The ~$0.20/gallon savings is insignificant even over long periods (for instance, it'll take you more than 25 fill ups to save $100 by going with cheap gas).
Dropping the octane increases the likelihood of knocking, even with sophisticated knock sensors. One good rattle and you're replacing head gaskets (although on a non-boosted car, this is less probable). These are relatively high-compression engines, so pulling out spark may not cure knock under all conditions, either.
I'll also wager that mileage will go down, since the car will not be running at peak efficiency any longer, and with less power, you'll need more throttle to make it perform normally. At best, it may be a 0 gain.
For four bucks, I'd skip it.
Dropping the octane increases the likelihood of knocking, even with sophisticated knock sensors. One good rattle and you're replacing head gaskets (although on a non-boosted car, this is less probable). These are relatively high-compression engines, so pulling out spark may not cure knock under all conditions, either.
I'll also wager that mileage will go down, since the car will not be running at peak efficiency any longer, and with less power, you'll need more throttle to make it perform normally. At best, it may be a 0 gain.
For four bucks, I'd skip it.
05-14-2008, 05:37 AM
#37
AudiWorld Super User
Join Date: Sep 2000
Posts: 2,771
Likes: 0
Received 0 Likes
on
0 Posts
A *much better* solution:
Drive all the time with the instant fuel economy being displayed in your DIS. Pay attention to it; try to keep it as high as possible.
Then, if you need it, you'll still have all your horsepower available because you haven't crippled your engine with low octane fuel.
This has been shown to increase fuel economy measurably. If it increases fuel economy by 1 MPG (this is about what I've gotten over the last 4 tanks) over the course of the tank, that buys you the same savings as switching down to the cheap gas.
(I read about this technique in a magazine that had some figures to back up the idea, but I'm now struggling to fine an online citation, though)
Then, if you need it, you'll still have all your horsepower available because you haven't crippled your engine with low octane fuel.
This has been shown to increase fuel economy measurably. If it increases fuel economy by 1 MPG (this is about what I've gotten over the last 4 tanks) over the course of the tank, that buys you the same savings as switching down to the cheap gas.
(I read about this technique in a magazine that had some figures to back up the idea, but I'm now struggling to fine an online citation, though)
05-14-2008, 05:39 AM
#38
AudiWorld Member
Join Date: Dec 2007
Posts: 523
Likes: 0
Received 0 Likes
on
0 Posts
Check your math: $4.00/fillup x once a week x 1 month = $16.
Not that you should be throwing money away (and I don't consider this to be frivolous spending), but I really don't see how someone who can afford such a car is going to sweat over this smallish sum of money. It'll take 25 fillups (nearly 6 months by your estimates) for this number to even approach $100, which is a good chunk of change. I'll bet there are a dozen other places where you can carve $100 out of your budget over 6 months and make it a non-issue.
If the car runs fine on the less expensive stuff and doesn't break, great, you've managed to save $4 a week. If it does break, how many $4 weeks will it take for you to pay for it?
Are you a gambling man?
If the car runs fine on the less expensive stuff and doesn't break, great, you've managed to save $4 a week. If it does break, how many $4 weeks will it take for you to pay for it?
Are you a gambling man?
05-14-2008, 07:02 AM
#39
AudiWorld Member
Join Date: Feb 2007
Posts: 524
Likes: 0
Received 0 Likes
on
0 Posts
Not sure about Audi, but my old car waited a certain amount of time before the ECU advanced timing
after retarding timing because knock was detected. That might be why you didn't detect anything. Plus I don't know if a Stock 2.7T would take advantage of anything over 95RON (91 Octane).
On my old car it was hours if not days before the ECU would adjust and forward the timing. I got really good at resetting the ECU but that had its own chalendges too since the ECU would have to relearn again.
On my old car it was hours if not days before the ECU would adjust and forward the timing. I got really good at resetting the ECU but that had its own chalendges too since the ECU would have to relearn again.
