I was wondering what most drivers are using in their 914's. 87, 92, 100?

I have heard that in fuel injected cars running with a higher octane gas than they were designed to run at can be a waste of money since they are set up to run on a specific octane and any more is lost. I have a Passat and the manufacture states 92 octane. My truck uses 87 and the dealer said I can do damage by running 92 ( although I have no idea why).

Please set me straight on my ignorance.

I always use 91 or better (as suggested on the silver sticker by my gas tank on my 914 that I assume is original to the car since it's in German). I'm interested in what others have to say too.

As high as available otherwise it runs like dodo.

The original stickers talk about "RON". US pumps are measured in "AKI", or the average of RON and MON. MON is 8-10 points lower than RON for a given batch of gasoline, so the 91 RON on your sticker is actually ~87 octane from a US pump.

Using higher octane than necessary is a waste of money, except to the extent that it makes you feel better about your car. It should not be able to damage anything (unless you put AvGas in the car, in which case you can have some interesting problems!!) but it won't really help anything. Not unless you can take advantage of it, perhaps by advancing the ignition timing or upping the compression ratio or the boost. (OK, so our cars can't do either of the latter in stock form...)

Actually, if you have a motor built for 80- or 85- octane gas (unlikely but possible if it's old enough!) and you decide to put some 100+ octane race gas in it, you might have problems with the mixture continuing to burn as it goes out the exhaust port. I believe some older aircraft did have problems with that at one point... But it is vanishingly unlikely to happen, or even come close to happening, with a car.

--DD

102! Custom mixture!

I had a camaro back in highschool. Nothing special. But I tried several times to put 87 in the tank. It would stop running completely. I changed the spark plugs and it ran again. At the time I didn't think to just try cleaning the spark plugs. But yeah it didn't run on anything below 92.

you only need and can use it if the design of the cumbustion camber requires it or compression demands it. i'm a m.p.g. checking fanatic and my old commutor (250.000 mile) 87 tempo 5-speed (we cant always drive a porsche) acually lost m.p.g. on 92 octain.

my wrench, who's worked with v-dubs and porsches for a few decades, says premium, so that's what i put in.

and it makes me feel like i have a high-end car or something.

~a

my engine is designed for 91 octain, so I fill in 91 octain

everything else would be a waste of money, IMHO

once I had to fill in 95 octain, because there was no 91 fuel available - I didn't feel any difference
and like a commercial for a Coca Cola wannabe drink here in Austria says: if you don't feel the difference - why pay the difference


I'd say it like Shakespeare - As you like it

Gustl

is there a compression ration/octane requirement type of guideline? (like, 7.4:1 to 9:1 requires 87 octane; 9.1:1 to 10.5:1 requires 89 octane, etc)

There is a married couple in my office and the guy is pretty much a car guy with a bunch of different cars. He's apparently a good mechanic as he does repairs I would never attempt. But for some reason he's hooked on high octane for all of his cars. One day I noticed his wife was driving the new Toyota SUV instead of her Civic. When I asked her how she liked it she complained about the lower gas mileage, larger fuel tank, the fact that he insisted she put in high test, and the resulting higher bills. I asked her what grade fuel the owners manual called for and she said 87 octane. I told her the high octane was a waste of money and convinced her 87 was fine. I also made her promise that she wouldn't tell her husband I said so!

91
i only fill it up about 10 times a year, so what's a few extra bucks

With my 2056 running 9 to 1 CR I have tried 87 and it pings alot....so its 91 and nice and quiet for me. I run standard 27 degrees advance too with the vac advance hooked up.

If you lack compression ratio higher octane fuel creates tuning issues, rich running and lack of power. The best rule of thumb is to try different fuels and note the power, temps and other engine characteristics and make the call for your engine by allowing the engine to TELL YOU what it likes...

Many, many times I see guys running race gas in engines that have street compression ratios, doing this requires more timing advance to help start the fire earlier to provide complete combustion- not doing this kills the power potential.

My 912E has ran 110K @9:1 on the current engine and I know the engine like a member of my family. In the summer it likes 91-93 Octane, but in the winter or even this time of year it likes 89 octane the best.

Try different fuels and drive with the radio OFF listening and feeling the differences... Take notes and use the fuel that the engine seems to like best.

I will say that I purposely build engines that operate best on premium fuel, the main reason being that the chances of getting a bad tank of fuel is greatly reduced when you buy the good stuff.. I buy my gas from the same station and even the same pump at every fill up that I possibly can- too many engines have been compromised with 87 octane fuel that was really 84 octane and filled with water...

Nope, not really. So many other factors influence it that there are no hard-and-fast rules that us mortals can apply. If you were a car manufacturer, you probably would be able to calculate it out (depending on combustion chamber shape, compression ratio, cam, etc.) but we don't have access to that kind of calculation.

--DD

I use to run 87 in the 914 for years (no comments please guys).
I started using premium lately, and have found that I get much better performance, not to mention much better gas mileage!!! For only .10cents more per gallon, its definalty not a waist of money. Actually, it saves me $24 a month to run 91!!!

My 86 toyota truck actually runs poorly when I use anything higher than 87. Dont know why. Maybe because its japanese and carburated

Dynamic compression ratios dictate the need for octane.. static CR, cam, valve sizes and even operating elevation and weather conditions dictate "Dynamic compression ratio"

Octane does not equate to a measure of how clean the fuel is. They are all transported in the same way in segregated tanks on clean product tanker vessels. The amount of water is a factor of residue in the tanks. When a ship cleans tanks between cargos they utilize heated water at high pressure to spray down the tank. After cleaning they pump the residue to a slop tank. They are never able to pump it all out and as a result a small precentage of water gets mixed in. The number of times it gets moved by a ship would increase the impurity levels. If the station is cutting the fuel I think the one to cut would be the high octane. Higher return on investment.

Isn't this as simple as "higher octane=greater resistance towards combustion"? A higher compression rating needs a higher octane fuel to avoid pre-detonation (pinging). It's all about providing the right conditions for optimal combustion in the chamber when that A/F mix is compressed to 8.5:1, 9:1, 10:1 etc. A low octane fuel in a 10:1 ratio compression chamber will most likely detonate too early.

My .02

What about the newer cars?

My wifes '01 Infiniti says 91 octane. Is it necessary?

Nope, BUT having talked to a rep from Chevron when I got a tank of bad 93 octane that melted a 20,000 buck engine on my dyno when it was really 87 octane I'd have to say that the lesser octanes have greater risks of impurities..

He told me that in my area they sell double the amount of 87 octane than that of 93, especially due to the current and recent gas prices. The more often the tanks are filled the greater the opportunity for impurities to be transferred from the tanker trucks into the tanks at the station..

That one instance is the only bad experience I have ever had with 93 octane fuel, I generally use 2500-3000 gallons per year on the dyno alone (as much as 3700 gallons in 2003 when I did a ton of cooling system testing)

Chevron paid for the engine in question because they had filled a 93 octane tank with 87 Octane-

Typically, yes, especially on newer cars. Today's calibrations are very complex and if the calibrators used premium, that's what your fuel/ignition maps are based on, not regular.

Ford uses the Jag V8 in the Lincoln LS and the calibration is for premium fuel. But, they were having a problem fouling plugs by the time the vehicles arrived at the dealers. So, they used regular for the 7 gallon plant fill just the keep the plugs from fouling. But then you had customers driving the cars when they arrived at a dealer and they would ping. No wonder Ford's losing money.

Many of you know I work in the motorcycle industry, and fuel is a major problem for several reasons.

At transport: fuel being removed from a sea going tanker, the fuel is not always segregated as previously suggested. but what is normally being shipped by a sea going vessel is the "base stock" of gasoline. This is what is delivered to distribution points and then different companies add their own additive packages. The important lesson here is when the gasoline is removed from the vessel, the removal of weight (fuel) has to be countered or else the ship can become improperly weighted, and that cg needs to be maintained. They do this by pumping sea water into the fuel tanks. Knowing that gasoline is heavier than water, the water stays down and the gasoline goes to the top, allowing for removal. Some one who must be a Mensa member thought this wasn't the very best idea, since that fuel contaminated sea water had to be pumped back out to refill the tank ata later date. In some of the newer tankers this method has been eliminated, by having a ballasting system that counteracts the "pumping off". One major drawback to the first system is the microbiological growth that can form (AND LIVE) in gasoline. It has a much higher chance of surviving in diesel fuel, as Jake and I (and others) know about from our background in aviation. Even though JP4 is good fuel, it can have microbiological growth that can lead to fuel tank sealant degradation, but thats another story, back to the question.

Once the base stock fuel is "refined", meaning the company has blended their additive package into the fuel, then it is normally trucked to a gas station or holding tank for consumers. The other way fuel storage tanks become saturated with water is condensation. This year in New England, we have had tremendous rainfall, and very high humidity. This increases the ground water levels, and provides for more condensation (water) to be distributed to the in ground tank. This can also lead to a ton of problems. Here's what is very interesting about blending, different chemicals that one company claims to "drive your engine clean" can raise the cost of the fuel by 10-20 %. If we know that the base fuel is the same, then we can easily conclude that the different price from regular (87)- super unleaded (93) is the cost of the additive packages. These addditive packages are what raise or lower the octane of the fuel. Some of the additives are detergents, some are octane additives.

The poster that earlier discussed the AKI standard, vs ron or research octane number. PLEASE UNDERSTAND WHAT OCTANE RATING YOUR BEING ASKED TO PUT INTO YOUR CAR. You may be camparing apples to oranges. Also remember that the profit margin on super unleaded will be higher than regular fuel. So it is in the gas companies best interest to market their higher octane fuel to you the consumer. I agree with Jake, listen to the engine, take notes on gas mileage, the engine will tell you.

Another thing in this post that I need to cover is ETHANOL. Most cars (not the 914) have closed loop O2 feedback that will monitor fuel mixture and compensate.
However the 914 is not one of them. Also many early FI systems do not rely on the O2 feedback when at WOT (wide open throttle). What we really need to know about ethanol is that the release of British Thermal Units (BTU's) is less than that of gasoline for the same volume. Meaning: to get the same amount of work from ethanol based fuel you will need more volume of ethanol based fuel to extract the same amount of work or horsepower. My testing on motorcycle engines using a four gas analyzer has shown a .75-1.0 % CO drop when using ethanol based fuel that has an ethanol content of 12%. When this happens, there is actually a RISE in hydrocarbon emissions due to lean misfires. So the EPA mandates this crap, presumably for clean burning, and it actually makes SOME vehicles run worse and produce more hydrocarbons.

On a political note, if ADM (Archer Daniels Midland) got their hands out of the pockets of the Senate and House of Reps, we would'nt have to deal with this shit.
Anyone thinking E85 (85% ethanol) is a good thing, needs to get a clue. Imagine how much more E85 you will need to burn to get the same power out of your car when using E85. This is not a smart plan. Forget about gas mileage or cost per mile of E85. The byproduct of straight ethanol can be very corrosive, you can plan on less engine life, and far more frequent maintenance visits for your car if you run E85. What a farce!

But anyway, what gas should you use in your car. The minimum octane so it doesn't ping, and does'nt run lean. I have always run my stock 914's on 87 octane fuel. Also remember that with carbon build up, your compression ratio could go up a little, and this may force you to run a higher octane. Again, only use the octane needed so it does not detonate. Anything else is an absolute waste of time......and money.


Erik Madsen

Couldn't the opposite be just as true? (Assuming that they don't clean out the holding tanks at the station.)

If a holding tank for 91 octane does get filled with gas that has impurities, then that gas sits in there longer (as people don't buy it as much). Therefore it's possible that it could actually increase the chances that your buying a tank full of gas with impurities as apposed to the low octaing holding tank that is being refilled more often. I guess you'd have to factor in how often you by gas vs how often a holding tank is being refilled.

Eric, That was an excellent post!

Thanks for all the input.

I have been running 91 octane in my car and it seems to be running well. I am going to drive the hell out of my car this weekend and wanted just a little more. The local 76 station sells 100 octane at the pump so I was thinking of running it hoping for just a bit more power. At @ $4.50 a gallon I was trying to decide if the extra octane may be worth some extra power. From what I can take from the answers I feel that I may just stay with the 91 octane.

I am running a 2.4 litre 6 from a 1973 911S with MFI and the compression is 8.5:1 . It runs like a raped ape with the 91 octane but I just wanted a little more kick for the weekend. For a extra $2.00 per gallon, I thought it might be worth a try.

If its been running fine on 91, leave it as is. Higher octane fuel, as stated above requires more CR to burn or advanced timing. If you have carbs don't be suprised if you need larger jets because the fuel viscosity is actually higher.. MFI can act similarly due to its characteristics.

So many times I see guys go to the track, dump in higher octane and then the car GOES SLOWER!!!!!!

If you don't want to retune a street engine won't make any more power on higher octane fuel if it lives well on pump gas normally.... BUT the engine will run a tad cooler..

If it runs fine keep your normal fuel in the tank...

Thanks

Now off to do some

If you put higher octane in.. turn up the boost too

I can safely run 18PSI on pump 91, but 22PSI on 108 VP. The 108 gets a bit more timing too

BJH

Erik,
What you posted is interesting. I do not wish to dispute any information other than that which is related to tankers. That is false information. CG is not maintained by displacing the cargo with sea water. The only displacement taking place is inert gas. I don't work in the motorcycle industry, so I will not comment on that. I will stick to the Maritime Industry which is my profession. I am curious to know what the classification of "base stock" is and what percentage of this stuff is transported in this form on clean product tankers? You seem to think that what I said was false, as it pertains to segregation. It is not. I wont even start to explain why even referring to CG as you did shows that you don't know.

Finding a sunoco with 94 octane ULTRA is like finding extra power with my Dellorto carbed, slightly modified 2.0 4-banger. Actually akin to pulling the bunched up floor mat out from behind the gas pedal in a typical car.... whatever those are..

-greg-

No test results, or reems of data, just that my life long Porsche mechanic & origional 6 racer said that 91 was not necessary. He said that I could use regular, which at altitude is only 85 octane. No problems yet although I do sometimes put in some 87.

When I use 87 my 914 will miss everytime . But when I use 92 or better there is never a miss This for me was a hard lesson to learn.

How often do the tanks get tested? once a year? I use 91 octane, but have noticed a variance in performance and milage from one tank to the next. Does anybody make a small test kit? I would love to be able to walk into the attendant and say, Why am I paying for 91 when the test here shows 87?

My $0.02...
Gas is LIGHTER than water. Erik, I know you know that by your description, just that you wrote "heavier" by mistake.

I don't know about gas tankers, but on my ship, a Spruance-class Destroyer, our engines were gas turbine units (4 @ ~20,000hp each ) and they used JP5 (jet fuel, which cars don't use). To balance the ship when fuel was transfered 'tween tanks sea water was used to "fill the gap". Since Combat Systems berthing -- where my rack (bed) was -- was directly on top of the fuel tanks we got to hear the loud transfers every time it happened. Point is, some ships use this method and some don't. For transporting gas I would think they would use methods to reduce polluting the product and filter/clean it as well before land transporting.

I run low grade in my 914 since she's stock. My other air-cooled (bigger engine) gets high octane due to higher compression and is jetted accordingly. Because I don't drive her as often the extra cleaning package that comes with the higher octanes give me the warm-n-fuzzies as well. My Jetta -- a daily driver and weekend SCCA'er -- gets high octane as well due to higher compression and as recommended by the after-market chip manufacturer (Techtonics Tuning here in Orey-gun).

I don't see the higher octane fuels as a complete waste of money since they contain their cleaning pacakages. And what swood wrote is the chief reason for high octane.

finally....some much needed validation in my life.

The owners manual recommends 92. I figured the engineers did it for a reason, other than owning gas stock.

In my stock injected 2.0 I ran regular (87 in AZ), sometimes midgrade (89 in AZ). For my stock injected 1.7 I ran super (91 here in az). So the extra MPG on the 1.7 was negated by the use of regular on my 2.0 - tank for tank.

Lower octain gas burns hotter and makes more power when compaired to the same motor running high octain gas. It also detonates easier.
But higher octain gas can be squeezed more, thus making more power as the lower octain would detonate too soon.

I run 87 on my stock 2.0 engine as recoemnded by Porsche on the sticker under the hood of my '76. I have never really seen much if any diference between the 87 and 93 octane fules. te only time I use 93 now is if I am also putting in a bottle of injector cleaner. Not sure why, but I feel like it is better to do it that way, although I have no evidence.

I was thinking about the octane ratings between the US and Europe a few weeks ago and when I was on my way to Stuttgart I popped off this picture of a pump there that clearly shows 91 ROZ is the equivalent of regular here in the states.

Click to view attachment

--Jason

I think the thing to take away from all of this is that the various types of pump gas are DIFFERENT. Premium is not better gas than regular - it is simply formulated differently in order to have different characteristics. Those characteristics allow it to be used properly in a higher performance (compression) engine than the regular gas, but premium is NOT in and of itself better or more powerful than regular.

Of course, that is how it is marketed, and how people perceive it. But like Jake said, your engine will perform better on one type of gas vs the other depending on your engines characteristics.

So people need to get over the perception that the higher the octane, the better and more powerful the gas is. You just need to run what is appropriate for your cars engine.

The fuel companies market the higher octane fuels as superior for a reason (it's also why they call it premium). They make more money from it. It doesn't actually cost more for them to formulate the higher octane fuel. It is artificially marked up in price in order to make more money. They can do this because they have created the perception that premium is really better gas and is better for your car. Also because those people who have the money to buy a car with a high performance engine can afford the extra cost of the premium gas.

I am only talking about pump gas here. Doesn't apply to race gas or avgas.

As I satated above a couple of times every engine is different and even the climate impacts the fuel that will make your engine run it's best..

I will say that my Pinzgauer military truck is the only vehicle I own that will run its best on 87 octane, thats because it has 7;1 CR and was made to run on anything... I have gotten 2 bad batches of fuel in one year in that vehicle (12000 miles), but have only gotten ONE bad tank in the past 109K in my 912E that runs premimum 90% of the time and at least 89 octane all the time.

Its a gamble every time you pull up to the pump, when you see as many melted pistons as I do from engine teardowns you'd understand why 20 cents a gallon is worth the expense if thats the fuel that your engine runs best on...

I build engines specifically to run on 91-93 octane, many times the added efficiency that I'm able to squeeze from the combo will gain the customer at least 2-3 MPG and thats certainly worth more than 20 cents per gallon-

On a NEW engine with computer controlled timing and fuel, put the grade recommended by the manufacture.

A higher grade won't do anything but cause excessive emissions and maybe poorer fuel economy. A lower grade will probably cause engine knock which the knock sensors will pick up. The computer will then retard timing to protect the engine, costing hp and efficiency.

The knock sensors will "hear" knock long before you do, so the old saying, "use the lowest grade that doesn't knock," does not apply to the newer cars.