Forgot to touch upon this.

Running the proper grade of gasoline allows the engine controller to maintain sufficient ignition advance to extract the maximum amount of power from the burning of the gasoline.

While the engine controller can sense incipient knock/detonation, and retard the ignition timing, thus saving the engine from destruction, it is not an ideal situation. In fact, it should be looked upon as simply the lesser of two evils.

Performance and fuel mileage will suffer. Enough so that one finds what he saves on gasoline at fillup is eaten up by having to fill up more often. IOWs, you end up burning more of the cheaper gas for a net gain of nothing.

Plus, or worse, because of the retarded igition timing, the fuel starts burning later in the power stroke and this results in exhaust gas temperatures being higher. Thus everything from the combustion chamber is subjected to a higher heat load.

Many think that octane matters only under full throttle but full throttle is a piece of cake, cause the engine controller can and does go open loop, thus it can ignore emissions and enrichen the mixture to provide protection against detonation without having to retard ignition timing.

It is those part throttle moderate loads to moderately hard loads that really cause problems. The engine controller must mind emissions so it can't go richer, so it retards ignition.

Not good.

Running a high performance engine on gasoline below its recommended grade of gasoline is false economy. In a pinch, not a problem. But for a steady diet....

Sincerely,

Macster.

 

Stale gas, do you really believe that? Gas stations refill their tanks every couple of days - it does not go 'stale' on that sort of cycle. That claim is bogus.

I also doubt the claim that higher grade fuel would go 'stale' faster - it's a hydrocarbon - it does not degrade that quickly, unless attacked chemically, or thermally cracked at high temperature. The additive package may change with time, but that would apply to all of the grades equally (assuming the same package used across all the grades of a particular brand). The timeframe for degradation is not days or hours, try several months - not something that can happen in a gas station that has customers, or a car that is getting used.

Octane variation is also bogus. All gas within a formulation has to be tested to be within spec. when it is transfered from the pipeline to bulk storage. You can't vary outside an octane range once it becomes a formulated fuel grade, it is what it is sold as... not unless the UK is less stringent on fuel formulations than the US and I doubt that.

As I said in my post, the additive package is not relevent in the US. Regulations ensure that the additive package prevents engine fouling and carbon build up. Sure you can go beyond the regulated minimum, but it has little effect, other than a marketing boost.

Your comments on octane are otherwise correct.

The fact that people buy into the comments in the article just goes to show how effective marketing can be.

 

Now, one issue we have not gotten into yet is the subject of fuel fraud, i.e. gas stations selling fuel that is not what it is claimed to be - not the franchise brand, or adulterated in some way.

This has been an issue in recent years and fuel companies go to great lengths to detect counterfeit fuel and will test for it on each delivery and during random inspections.

 

You certainly are kidding about this point. Variation exists in everything. Just because the government "certifies" it does not mean much. The measurement systems alone can vary greatly. I have not specifically studied these measurement systems, but have studied FAA and FDA certfied measurment systems for 2 decades and found many to be are entirely incapable (so much for government certifications). Do you know the spec, BTW?

All in all though a good discussion.

 

Sure there's varation, but the question is whether it's significant variation and I would argue not, otherwise it's pointless having a spec. and measuring towards it.

I don't know the spec., but I'm sure we cold find out easily enough.

 

20 Gallon

 

So, that's basically a 3 mpg difference and within error. I know when I fill up my SUV (a 21 gallon tank) that my milage varies by as much as 4 mph on a regular basis.

 

It is incorrect to state that: " engine controller can and does go open loop, thus it can ignore emissions and enrichen the mixture to provide protection against detonation without having to retard ignition timing as this is independent for what octane you are running". The ONLY control related to octane at WOT besides the pre determined program are the knock sensors. If you knock, you lose timing and power. There is no change in fuel enrichment regardless of whether you are running 100 octane or 87 at WOT.

 

Good catch - I'd missed that.

With regard to octane specs. A quick Google search reveals that octane ratings are mandated minimums, therefore, you only gain by variation - if it's 91 octane, then it really means that it's 91+ octane. i don't think we can really complain about that kind of variation.

 

The summary of this thread so far is that there are lot of myths and untruths out there.

 

Just me being a smart*ss, but we've also learned you are not capable of editing one of your previous posts and so you just keep adding posts?

Sorry, just a statisticians sick form of humor (ignore the man behind the curtain).

 

but simply the engine controller's attempt to meet the required torque demands by the driver. At most other times, the driver's demands are tempered with emissions compliance among other things. (In some cars, torque output is limited to prevent drive train damage.)

But at WOT the assumption is -- for now anyhow -- that meeting the driver's demands is paramount, albeit not at the risk of letting the engine detonate itself to pieces.

At WOT (or at some point a bit below that) the engine controller can and does go open loop and enrichens the mixture some (not gobs but enough) to provide maximum power.

I see this while driving my car while monitoring various engine controller parameters, outputs during various engine operating scenarios.

Sure, if knock or incipient detonation is detected the engine controller will still attempt to counter it by retarding ignition, but under wide open throttle ignition advance is not as advanced as it will be at other times, under less severe throttle openings.

The engine controller also goes open loop under closed throttle coast downs....

Sincerely,

Macster.

 

The computer does exactly what the program was written to do based on various sensor inputs. It has no idea nor does it care what the driver wants. It is a calculation and will ALWAYS do the same thing if input is equal.

If your timing is programmed to be at 26 advanced at WOT under specific temps, air flow, etc, then (everything remaining the same) it will be at that setting whether you run 89 or 93 octane fuel UNLESS the computer receives a signal from a knock sesnor telling it shut down the timing.

 

Ouch. Justified, but ouch.

 

I have learned a lot from your posts guys. Excellent links. Sounds to me like there is definately different gases out there sold by different companies but that you cannot be assured that the say exxon gas you are buying is not shells because of economies of shipping vs swapping from competitors. Furthermore most of the base fuel is the same it is the additives we are interested in. Very interesting stuff indeed.
I still kind of wonder if one manufacterer has a prefered additive package, especially since all these articles seem to say the additives are expensive. So one would think a cheap brand may not add much compared to a "high end" brand. Wish there was more info on this.