What octane gas do you run?, Is higher always better ? Or just a waste of $$$ Options

[Michael N]

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. (IMG:style_emoticons/default/sad.gif)

[rjames]

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.

[So.Cal.914]

As high as available otherwise it runs like dodo.

[Dave_Darling]

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

[porschecb]

102! Custom mixture!

[turboman808]

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.

[orange914]

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 (IMG:style_emoticons/default/chair.gif) (we cant always drive a porsche) (IMG:style_emoticons/default/confused24.gif) acually lost m.p.g. on 92 octain. (IMG:style_emoticons/default/headbang.gif)

[double-a]

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. (IMG:style_emoticons/default/biggrin.gif)

~a

[Gustl]

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 (IMG:style_emoticons/default/confused24.gif)
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 (IMG:style_emoticons/default/biggrin.gif)


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

(IMG:style_emoticons/default/wavey.gif) Gustl

[type47]

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)

[maf914]

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! (IMG:style_emoticons/default/laugh.gif)

[TROJANMAN]

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

[Bleyseng]

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.

[Jake Raby]

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...

[Dave_Darling]

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)

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

[Toast]

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 (IMG:style_emoticons/default/tongue.gif)

[Jake Raby]

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

[Leo Imperial]

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.

[swood]

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

[Allan]

What about the newer cars?

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