True Confessions - Premium Gas
 

Curious how many Boxster owners are faithfully using Premium gas on a regular basis?

assuming 12k miles per year, 20mpg, $3 premium, and $2.75 regular, a switch from premium to regular would save you a whopping . . . $150 -- per year.

premium always.

Premium...Period. If the book says so I will comply!

Usually, premium but sometimes super or plus (the mid grade). From what I can tell there's no difference in performance.

'04S
bob

I use premium always. Dux above points out the marginal savings in going to regular which is usually .25 less. Respectfully, this is no place where you'd want to skimp.

If you use anything other then premuim make sure that you use Chevron Fuel System Cleaner every 3k.

Nothing but the finest premium unleaded Chevron fuel for my baby. Same goes for my Lexus LS400. The Honda Accord, however, gets the cheapest unleaded I can find in town!

Porsche knows a lot more about the car than I do. So it will be premium.

premium gas
 

Chevron Supreme 90% of the time, Shell Premium 10%.

Hi,

The reason you want 93 Octane or better Fuel is that higher Octane Fuel can be compressed more before spontaneously combusting. It does not have any more Power (read Energy) than Regular 87 Octane, in fact in some instances it may actually contain less Energy depending upon which Octane Boosters are used.

When your Engine takes in a mixture of Fuel and Air, the piston compresses it. This raises the Temperature of the Mixture a couple hundred degrees above ambient Temperature. The engine is designed to compress the Mix to just Under the point where it will spontaneously combust and the spark from the ignition supplies the final amount of energy required to get it to burn. It's important that the Fuel/Air Mix doesn't combust prematurely as the rotating Engine is in the wrong part of it's Cycle and serious damage can occur. By differing the Chemistry of the Fuel, one can change it's combustion point to match the compression which the Engine produces.

The Boxster M96 Engine has a Compression ratio of 11:1 which is really quite high for a Naturally Aspirated car. You need to use a Fuel which can withstand this degree of compression without spontaneously combusting.

Because these Cars are run in different climates, temperatures, and altitudes, throughout the World, the Octane actually required differs slightly as well. But, to be all-encompassing, Porsche has specified that 93 Octane Fuel be used. This Octane level will not detonate until the right moment in all circumstances.

But, this level Fuel is not always available in all markets, so the DME is capable of compensating for lower Octane Fuel - down to 89 Octane. It does this by literally listening for pre-detonation (or knock) to occur with a Knock Sensor located on each bank of Cylinders. A Knock Sensor is really a sort of microphone and when it picks up the sound from a knocking Cylinder, the DME retards the Spark, that is, makes the Spark occur earlier in the Engine Cycle to control the detonation of the Fuel. You can retard the timing only so much on an Engine. and in this case, it does so sufficiently to use 89 Octane Fuel. The downside to this is that when you retard the Spark, you also reduce the Power the Engine can make (in this case, somewhere in the neighborhood of 5-8HP).

You can use whatever Octane Fuel which does not produce Knock. The problem is, you can not always tell when your Engine is Knocking so using the recommended Grade is a smart thing.

Also, all Gasoline is essentially the same. The Various Brands do not operate their own refineries. All the Gas is produced in Bulk at one of a limited number of refineries and then shipped via pipeline to various Terminals throughout the Country. It is at these Terminals where the various proprietary additives, including some Octane Boosters, are mixed with the Raw Gasoline and it is then trucked out to the Stations to be sold. BTW, while many Companies have proprietary Additives, these vary only slightly from one another, and are in the same Chemical Families and do the exact same things. The differences are TOTALLY for Marketing Purposes - so you buy Brand X instead of Brand Y. There are no definitive tests proving one Brand is better than any other.

There can be wide variations in the actual Octane Rating of a Fuel. For instance, here in the Mid-West, and other parts of the Country, Fuel changes with the Season. Here, they add up to 10% Ethanol (grain alcohol) to reduce pollutants in the Winter months because the Cold inhibits their dispersal and concentrates them at Ground Level. Now, Ethanol is an Octane Booster, so when it's added, the Fuel's Octane raises about 0.5 - 1.0 points (even though the Pump still says 87, 90 or 93 Octane). But, Ethanol, while it will raise the Octane of a Fuel, contains less Energy than an equal volume of Gasoline, so you experience a slight drop in MPG as well.

The Rating on the Pump is the Minimum Rating for that Fuel. In actuality, the Octane can be several points higher as a result of different Crude(s), or Batches produced - there is a significant variation in refining it. This is why you can sometimes get by with using lower grade Fuel (because it's actually higher grade than the Minimum Rating it carries), but again, you can never be certain beyond the Minimum Rating posted for that Fuel, this variation can differ from Truckload to Truckload, or Tank to Tank.

Considering the minimal cost difference, the drop in Performance and potential for serious damage, in a Pinch it's OK to use a lesser grade, but I would not recommend a steady Diet of it for your Car...

Happy Motoring!... Jim'99

After purchasing my 98 4 weeks age, I started using 93 (Shell and sinclair) and the engine immeadiately ran smoother. I was surprised by the difference.

I agree this is no place to skimp. With the considerable cost of maintenance on a porsche, premium fuel is the only way to go. I prefer chevron 93, only go w/ another brand if I must.

Jim has some good points. In my previous life I had to inspect bulk fuel terminals. As Jim stated, they don't have separate tanks for each vendor. The only separate tanks are for the different Octane Ratings. Chevron tankers load up right next to Wal-Mart and others. Next to the loading stations is a VERY small shed containing tanks with each vendor's "proprietary" fuel additive. These tanks couldn't have been more than a few hundred gallons each. Compare this to the bulk tanks which are in the millions of gallons range. So, you know there's only a miniscule amount of additive per gallon. I'm not saying that some additives aren't better or more effective than others - but there is absolutely no difference in the base fuel.

As to getting more power from higher octane (or less power from lower octane), I'll defer to Jim on that one. But, I did see an interesting Speed Week last night where they actually took a 997 and dyno'd it with regular and then with premium. They reported a 5hp difference between the two.

Premium in my tank
 

Very instructional reading. You must be a mechanical engineer! Appreciate your insight on the subject. I do use premium all the time. Money wise it does not hurt the bottom line in my daily usage of 20 miles a day therefore I use the premium gas. I am a firm believer of what the manufacturer recommends for the car. Whether it is tires or gasoline I follow the prescribed recommendation.

The point there is that you're not getting MORE power from the higher octane fuel, you're getting LESS than you're supposed to get by using the lower octane fuel as the computer retards timing to compensate for the lower quality of the fuel.

Hi,

Thank you for your kind words. I am not a Mechanical Engineer, but do have an Engineering degree, also a Science degree and I took waay more Chemistry than any Human Being should ever have to.

The truth is, I've hung around Motorsports for so long, that you learn this stuff by osmosis if nothing else. Also, I have a longtime friend with whom I co-owned and raced a Formula Ford some years back. Coincidentally, he is the Safety Director at the Ashland Oil Company Refinery at Pine Bend here in Mpls., where about 80% of all the Gas consumed in the State is refined, so I've had the $0.25 Tour several times...

Happy Motoring!... Jim'99

93 Only
 

This would make a good survey, though it seems most people here are following their manual's recommendations. The manual notes that the less octane can throw the check engine light.

Hi,

Sure, makes sense. If the DME cannot adequately compensate for the lower Octane it would cause a MIL.

An Engine may operate fine on the Lower Octane, with the DME compensating for it. But, put the Engine under Load (High Speed, Passing, Going Uphill), or raise the Ambient Temperature (lowering the detonation threshold) and suddenly it cannot cope, which it signals to you in the form of a MIL. I suspect that you'd feel the loss of Performance just as the MIL came on too. Also, an Engine which is Knocking has to cause Havoc with the Emissions Readings from the O² Sensors too...

Happy Motoring!... Jim'99

I use premium gas at every fill up. Why buy a premium sports car only to use cheap gas? If Porsche recommends 93, then 93 is what my car drinks.

93 octane all the way, and if I can't find it I will add octance boost.
The way I see it, if you can't afford the $0.20 extra per gallon then sell your car and get a Honda.

Um, yeah, that was kinda my point. I simply thought it interesting that someone actually quantified the effect or timing retardation on a Porsche!

I am all for using 93 and don’t willingly go for less.

When we did our cross country drive though, we ran across a number of gas stations in the desert that didn’t carry anything above 87. Since the choice was 87 or nothing, we wound up going with that a few times. Honestly, I couldn’t tell any difference, but I imagine it wouldn’t be good to use for the long term.

91 octane Esso premium gas here. As far as I know, only Sunoco sells anything higher (94) in Toronto and there are none near where I live.

Sorry, it sounded like you were saying that the higher octane fuel makes power, but that regular octane fuel is fine. I just wanted to clarify that. If people get that in their heads, it might make penny pinchers start doing bad things. :)

But, I think it's also important for people to know that lower octane fuel WON'T blow up your car. If you end up having to fill up where they don't have the proper octane or anything close to it, you can still drive on it, but you would definitely have to do the "drive like there's a raw egg on your gas pedal" thing. Drive like a grandma, so to speak!

Hi,

A couple of points. There is a difference between the Power an Engine can make and the amount of Energy contained in the Fuel.

Gasoline contains about 30,000 Calories in a Gallon (one of the most Energetic Fuels in existence). But, once you start adding other compounds such as De-Icers, Octane Boosters, Lubricants (yes there's some light Crude in Gasoline), you no longer have a full gallon of pure Gasoline, it's been dilluted.

Unless those additives in combination contain 30,000 Calories/gallon or more, you have lowered the energy content of the mixed gallon of Fuel.

And few additives contain that many Calories/gal. so the higher the Grade, the less energy it contains. Your Engine may well make more Power (because the DME isn't retarding your timing), but you will not get as high an MPG from it - you will burn more of it to produce the same amount of work. This is significant because the closer you can stay to Raw Gasoline, the better your Fuel Economy will be and the lower your operating costs.

But before anyone thinks they can Cheat the Fuel Gods and fill-up half & half with Reg. and then Premium thinking they've saved a couple bucks, but raised the Octane content sufficiently to operate properly, realize that the different grades have different specific gravities, so one will Float on top of the other and you'll be burning Reg. for half a Tank and Premium for the other half.

I'm not sure I fully agree with your statement regarding not blowing up your Car should you run on 87 Octane. Aside from the issue of Knocking, you can have a variety of unburnt combustion products running through your Cats which will shorten their life as well as that of the O² Sensors. Plus, any ill effects on will be totally dependent upon circumstances. You may not have a problem driving an empty Car though the Nebraska Flatlands on a 30° Day at 50MPH with the CC on, but load up the Car with Passenger, Luggage, full Fuel Tank, or drive Up the Rockies or through the Desert at 120°F, and you could create serious problems. Ambient Temperature, Altitude, and Load are major contributors to Knock. Ever notice when you hear an old Car knocking it's usually accelerating or going uphill?

A better suggestion would be to carry some Octane Booster (a couple cans at least) if you're driving through a strange area where you're unsure of the availability of the proper Fuel. Also, inflate the Tires a couple of extra pounds to decrease the Rolling Resistance and reduce the Load. Don't run the AC or any other component which might cause the Engine to run Hotter either. Hope this helps...

Happy Motoring!... Jim'99

Which begs the question.. what are the recommended products for this? I have a feeling that there'll be alot of snake-oil in this market.

Hi,

To answer your question, not really. All of them work as advertised (the Chemistry is simple), so Price should be your only consideration, which varies widely - up to $80/gal. depending upon the Brand and the size containers you buy. This is why there's so much Hype between the various Brands, the Profit Margin is HUGE!

Octane Boosters can be broken into three types based on their active ingredients. Methyl Cyclopentadienyl Manganese Tricarbonyl (MMT) and Ferosene are used in limited amounts in off-the-shelf Boosters. The majority of Commercial Boosters use MMT.

Another type of Booster uses alcohols or aromatics as the active ingredient such as Toluene. Toluene, is an Aromatic Circular Hydrocarbon Chain with an Octane value of 110. It is a regular component of Pump Gas and is available in various grades at Chemical Supply and Home Improvement stores. Due to it’s cost compared to MMT and Ferosene, Commercial Manufacturers rarely use Toluene based formulas.

Premium Street Gasoline contains roughly 3 to 5% Toluene, to aid it's Octane characteristics. Unocal's 100-Octane Race Gas (which I use in my Formula Vee) contains almost 25% Toluene.

As a side note, in the 1970’s, when Formula 1 Cars were Turbocharged, they ran on Toluene. This allowed them to run the Turbo Boost to about 2 BAR (almost 30 PSI). Because of Toluene's lower Combustion Temperature (as compared to Gasoline), and somewhat unique detonation resistance, the Boost could be raised about .5 Bar (7.25PSI) Higher than if 100-Octane Racing Gas was used. In order to comply with the Rules, it was laced with a 10% mix of 87 Octane Pump Gas to Lower the Octane rating to the regulation 100 Octane, while keeping the advantages of a 110 Octane Fuel.

One drawback to any of these Additives is the diminishing effect they have on Higher-Octane Fuels. Adding the Booster to 87-Octane Gas will raise the Octane Value much more than adding a bottle to 91-Octane Premium Gas.

Excessive concentrations of these Additives can also damage Emissions-Control hardware, such as Spark Plugs, Injectors, O² Sensors and Catalytic Converters. This is why off-the-shelf Boosters have an emissions-legal street formulation which meets the Government-Regulated concentration of MMT or Ferosene. In any event, you should restrict it's use to no more than a 15% mix.

There is such a thing as Too High an Octane Fuel. If the Octane is too High, not all the Fuel burns in the Combustion Chamber and can lead to Burned Valves and Exhaust System Damage.

Probably the two most popular Commercial Octane Boosters are: Nitrous Oxide Systems' (NOS) Octane Booster, and Outlaw's Super Concentrated Octane Booster. Nitrous Oxide Systems' (NOS) Octane Booster uses MMT as its active ingredient, while Outlaw's Super Concentrated Octane Booster uses Ferosene.

A Home-made Octane Booster using Toluene can be made for about $14/gal. by combining 1 Gal. of Toluene, 31.25 fl.oz. of Mineral Spirits, and 3.5 fl.oz. of Automatic Transmission Fluid (to act as a lubricant). IMPORTANT: Use appropriate MSDS and Flammability cautions if making at Home. If added to 10 Gal. of 87 Octane Fuel (a 13% mix), this will give you an Octane Value of 89, the minimum required. If added to 90 Octane Fuel, it will raise the Octane Value to 91.5.

As I said, if you are traveling to unfamiliar remote areas, bring some Booster along. Buy only enough lower Grade Gas to get to an area selling the proper Grade. Hope this helps.

Happy Motoring!... Jim’99

Just a quick correction...

Retarding the spark actually makes it happen *later* in the cycle, not earlier. The earlier the spark happens, the more *advanced* the spark is.

Just didn't want anyone to go down the wrong path based on this...

Jack

Hi,

Of course you are right! Oops.. You guys don't let a thing slip (which is good!)Didn't catch that one - fingers faster than Brain... again!

But, the DME does retard the Spark, that is, produces it Later in the Engine Cycle. It does this so some Fuel remains unburned and consequently, the Pressures and Temperature in the Combustion Chamber are lowered, raising the Knock Threshold.

Happy Motoring!... Jim'99

MNBox wrote: "But, the DME does retard the Spark, that is, produces it Later in the Engine Cycle."

You are correct in your revised statement... The DME *retards* the spark timing when it detects knocking from the use of low octane fuel.

The low octane fuel burns quicker, igniting faster, which forces the retarded timing.

That just flies in your earlier statement, which bears correcting.

Happy motoring!

Jack :)

Hi,

Not at all, well sort of... I gave an incomplete answer. I was trying to give a brief answer without giving a Course on Internal Combustion Engines. I suppose you could start every explanation with: In the beginning, God created the heaven and the earth. And the earth was without form, and void...then in the 1880's, Gottllieb Daimler and Karl Benz...... just kidding...;)

In addition to retarding the Spark, the DME interupts the Fuel Injector Cycle, shortening the duration and therby injecting less fuel.

By adding less Fuel, you effectively increase the volume of the cylinder (by the amount of volume the Fuel would have taken up). This means that the Piston can travel Higher in it's Compression Stroke before reaching a Detonation Threshold.

Then the retarded Spark is supplied to add an extra measure of insurance against continued Knock for the reasons I have already stated.

Happy Motoring!... Jim'99

This is why I said "drive like a grandma". Do not put a lot of load on the engine--drive the car like you're trying to get the World's Greatest Gas Mileage. Any kind of load is going to cause problems so yeah, doing a hill climb with a trailer attached probably isn't a good idea. :)

My point is simply that if you're in a bind, 87 won't blow up the car. I didn't say anything about it being bad for the cats or what not. Sure, it's not going to be the greatest thing for the car and hell, you might even hear some backfires, but it's not going to destroy the engine. If your choices are to tow the car a hundred miles out of your way and lose a day's worth of travel, it's not a big deal--the computer is your friend!

I'm a bit surprised to see you suggest octane booster though. That stuff has been pretty universally shown to not raise octane by any appreciable amount--in most cases it raises octane by less than one number. You'd need a couple gallons of the stuff to bring 87 up to 91.

Here's one page that has some test figures, veracity unverified by me though:

http://www.gtatech.com/news_au_articl.html

Hi,

I think our disagreement is a matter of degree. I agree that gingerly operating the Car can, in some instances, get you out of trouble without the expense of a Tow, but not in all circumstances. I believe one should be over-cautious when giving this type of advice to those who may be less knowledgeable.

I just read a post on another forum where the lister heard a strange noise from the engine, but didn't want to pay for a tow, and the engine was still running, so he figured he'd be OK. After the noise didn't go away in 30 minutes, he decided to pull over. Diagnosis: Blown Engine! Sounds incredible to me, but there are people out there like this.

So far as Octane Boosters, the figures I quoted are from an independent test in which over three identical tests - the same operator, on the same CFR Engine got results within 0.02 Octane. 3 identical tests by different Operators, on different CFR Engines confirmed these results within 0.07 Octane.

You can find many conflicting tests, and those which are Dyno-based are within the degree of accuracy of the improvements, so offer little definitive proof. As you know, Internal Combustion is a very controlled and predicatable process. The Chemistry doesn't lie - these Additives MUST raise the Detonation Resistance of Gasoline, unless one is operating in some Parallel Universe where the Laws of Physics do not apply. And, the difference of even a few 10ths of an Octane can prevent Knock. And, don't forget, the Oil Companies use these very same additives to do exactly the same thing - raise the Gasoline's Octane Rating.

But I agree with you that in 6oz. or 12oz. quantities (like the packages sold in Auto Parts Stores), the results achieved are on the order of tenths of an Octane Point. You need at least a 10% mixture (which on a Boxster's Full Tank amounts to some 1.7 gal. of the stuff). We are talking about an Emergency situation, similar to your advice to driving "like a Grandma...".

I do not advocate it's use in day-to-day Driving on so many levels. Potential Damage to Valves, Exhaust and Emissions Equipment. And the fact that it costs about a third again the cost of a Fill-up. But, in this context, I would recommend having a bottle or two along with you on a trip, just in case...

Happy Motoring!... Jim'99

I agree that temperature, altitude, and load are contributors to knock. But that old car knocking is generally because that vehicle doesn't have the modern computers capable of adjusting the spark timing and air-fuel ratio.

In truth, an increase in altitude would decrease the necessary (R+M)/2 number by 1-2 per 3000' elevation. As such, octane numbers for gas in the Rocky Mountain region are lower than those in lower altitude areas (87 is considered "mid-grade" with 89 to 91 as the "premium" here). As such, wouldn't you actually be better off increasing in altitude with 87?

I always put Premuim in my car, never once cheated :)

I always put in the premium stuff, never cheated

KRZ

Hi,

Agreed on all point. My mention of the Rockies was not in reference to the Altitiude, but to the Load imposed on the Car by going UP (I should have been more clear). I agree tha lower density raises the detonation threshold, because lower compression pressures are achieved and there is less O² to oxidise the fuel...

Happy Motoring!... Jim'99

Mmm, yeah I see your point, I agree with you on all of that. None of this is recommended!

At these prices buying anything but premium seems like your overpaying.

Incidentally there are some differences other than marketing between different brands. Some use only imported middle east Crude. My understanding is that Texaco, Sunoco and Chevron don't use mid east crude and have drilling in South America and other parts. Something to consder while we are at war.

btw, this gas bull**************** has me investing heavily into energy. Valeo Energy (VLO), Sunoco, XTO, NOV, EOG ALL up up 100% in 12 months. I don't know who are going to make more dough in 2006, the energy guys or the financial services/credit card guys who just increased mininums payments on the staggering credit card debt of America.

Me too, I mean, what are you saving by using other than premium?