Fiat 500 Forum banner

1 - 20 of 30 Posts

·
Registered
Joined
·
25 Posts
I'm interested to know the answer to this as well... my guess is premium because it has a high compression engine. My Smart Car is the same way.
 

·
Registered
Joined
·
393 Posts
always better to go with the higher octane. Being this is a new car, do it right from the start put 91 at the minimum. 94 octane is widely available where im at, and works out to be a few dollars more on a tank of gas compared to 91. 94 just makes sense!
 

Attachments

·
Registered
Joined
·
19 Posts
Most modern performance cars that recommend premium will be just fine on regular, but they may not produce all of the horsepower they can. Octane only reduces the tendency to pre-ignite, so ignition timing can be advanced a little more without pinging. In most of your driving situations, you would not notice a difference in performance. Your engine should have some sort of knock-sensing technology (there are several) that will allow it to adjust to crappy fuel. Ever been to Montana? Last time I was there, regular was 85 octane. Not much power on hills, but the car survived.
 

·
Super Moderator
Joined
·
1,385 Posts
Premium -- because of the high compression ratio. Using a low enough octane could cause piston knock from premature ignition. The yahoos at the dealership filled mine up with 89 octane, but it seems to be running all right.
 

·
Registered
Joined
·
1,550 Posts
Yeah the dealer said it takes regular and filled her up with 87. I topped it up with 91 once I hit a 1/4 tank. I only use 94 octane in my Volvo, but then again it is turbocharged and modded. The higher octane makes a noticeable difference.
 

·
Registered
Joined
·
233 Posts
Yeah the dealer said it takes regular and filled her up with 87. I topped it up with 91 once I hit a 1/4 tank. I only use 94 octane in my Volvo, but then again it is turbocharged and modded. The higher octane makes a noticeable difference.
Wow, you already modded the engine after having the car for a week or two? Not worried about the warranty I take it?
 

·
Registered
Joined
·
13 Posts
Yeah the dealer said it takes regular and filled her up with 87. I topped it up with 91 once I hit a 1/4 tank. I only use 94 octane in my Volvo, but then again it is turbocharged and modded. The higher octane makes a noticeable difference.
Wow, you already modded the engine after having the car for a week or two? Not worried about the warranty I take it?
I believe it's the Volvo that's been turboed and modded.
 

·
Registered
Joined
·
99 Posts
I only use 91 octane E 10. Such a small engine needs all the help in can get. I figure the difference in cost on a fill-up to be abut a dollar or so. I really don't pay attention.

A modern engine should be able to run on anything this side of lighter fluid without knocking and damaging the engine. They can sense detonation and retard the timing accordingly. To some limit. I have no idea where that would be.
 

·
Super Moderator
Joined
·
1,385 Posts
Bottom line, the recommendation in the owners manual is to use a higher octane fuel, not regular. I take this very seriously, because it's like the "dishwasher safe" label. You know darn well if there was any way they could recommend nice old cheapest price point Regular, they would have. The fact that it is written there in black and white should be a word to the wise, or in fact, anyone with a normal IQ.
 

·
Registered
Joined
·
19 Posts
OK, let's start with what octane does: It decreases the volatility of the fuel, and thus helps stave off pre-ignition. It will not make a given engine more powerful unless the engine is tuned (or has the electronics to tune on the fly) to take advantage of the resistence to pinging.

High compression ratios and advanced ignition timing are ways to take advantage of higher octane ratings to make more power. Obviously, comression ratio can not be varied in a production engine right now (although much research has been done on the subject by SAAB and others) but ignition timing can be easily changed. Most modern engines have a knock sensing system in place and will change ignition timing and mixture to keep the engine from damaging itself.

10.4 to one is not that high a compression ratio for a small-bore engine; motorcycles are routinely 12.5 to one or higher. You may make more power on premium, but in a normally-aspirated engine you are not likely to cause any damage by running regular or mid-grade. The engine will simply adjust around it.

Fiat recommends premium. It is the easiest way to make sure there is a safety margin for all conditions, loads, and fuel qualities that owners may encounter across the country. As they say, "Your results may vary!"
 

·
Registered
Joined
·
18 Posts
Most modern performance cars that recommend premium will be just fine on regular, but they may not produce all of the horsepower they can. Octane only reduces the tendency to pre-ignite, so ignition timing can be advanced a little more without pinging. In most of your driving situations, you would not notice a difference in performance. Your engine should have some sort of knock-sensing technology (there are several) that will allow it to adjust to crappy fuel. Ever been to Montana? Last time I was there, regular was 85 octane. Not much power on hills, but the car survived.
This topic has been beat to death on the smart car forum -- it actually requires premium, but even it will run on regular. Running premium allows the computer to adjust and you can get a little more HP out of it (are you using it anyway?). My Honda van was the same as the 500 -- premium, recommended [for highest performance (it's a van, right?)] but 87 was OK. I put 180,000 mi on it before the daughter parked it on it's roof in a ditch (everybody was OK they were wearing belts like they were taught). I got as good or better mileage as anyone else and never had ANY problems with it. If you live in the Mountains or really load up your 500 then you MIGHT notice a bit of difference, but my guess is that 95% of people won't notice any difference at all. Now the turbo motor (in the Abarth) should be run on premium due to the higher compression ratios.
 

·
Super Moderator
Joined
·
1,385 Posts
I just feel safer running premium. Unless/until someone explains to me exactly how the system "senses" and adjusts. Not saying that it doesn't adjust, I believe the modern systems can do this. But is there any damage incurred while "sensing" the octane? I don't think the system is doing a chemical analysis of the fuel. It's probably detecting the pistons getting knocked back sooner than they should be. And if that's how it works, I will pay the extra couple dollars per tank, to avoid that scenario.
 

·
Registered
Joined
·
4 Posts
I just feel safer running premium. Unless/until someone explains to me exactly how the system "senses" and adjusts. Not saying that it doesn't adjust, I believe the modern systems can do this. But is there any damage incurred while "sensing" the octane? I don't think the system is doing a chemical analysis of the fuel. It's probably detecting the pistons getting knocked back sooner than they should be. And if that's how it works, I will pay the extra couple dollars per tank, to avoid that scenario.
The engine has at least one, and more likely two sensors called knock sensors (one high frequency one low frequency) the type of engine knock that you'd be likely to hear (on an old car this would never happen on a new EFI car) is a low engine speed knock if you were lugging the engine, however this is not the type of knocking that is dangerous or damaging to the engine- the damaging knock occurs at high RPM and at a frequency too high to be heard by humans.

The computer "listens" for knock something like 1,500x/second, if any knock occurs it automatically retards the timing to avoid the knock.

I'm not sure about modern 2011 systems but in the late 80's when these systems were first developed they were capable of retarding the timing and avoiding knock somewhere around 50 adjustments per second, they were surely limited by processing times.

In other words, I personally do not believe that running 87 or even 85 octane would damage your engine. Electronic fuel injection is incredible because it can almost infinitely compensate for anything you throw at it, temp/altitude/bad fuel etc.

I believe fuel quality far outweighs AKI rating, my BMW doesn't like 87 but it will run it, at the same time 93 from Shell or Mobil runs worse than 87 from Arco.

Finally, you'll get better mileage on 93 so it's all a net wash anyway:cool:
 
1 - 20 of 30 Posts
Top