Simple octane question...

[Geo31]

Octane is NOT a rating of how fast the fuel burns. It is a rating of resistance to auto-ignition. There is a difference. Higher octane does not mean slower burning.

[Dantilla]

I guess there is no such thing as a simple question about octane.

[AaronM]

[QUOTE]Originally posted by Ferrara_racing

Originally posted by AaronM
104+ the Sunoco racing fuel?

Or "104+" the trade name for a fuel system cleaner that adds something like 0.02 octane points to a tank of gasoline but does do a pretty good job of removing gunk from injectors?

The latter will definitely give you an improvement if your injectors are getting a little dirty.

The former will not burn completely in an engine designed for 87 octane and will actually create excessive deposits.

EDIT: The majority of "octane boosters" also have very high detergent concentrations and the improvement that they provide does not come from the minute increase in octane rating, but rather from the cleansing ability. Running a bottle of Techron through your engine (something I like to do at least once a year, preferably twice) will give the same or better improvement.

I know the difference between injector cleaner and 104+, techron is supposed to be a good cleaner and is recognized by Porsche but provides no boost in performance that I could feel. A bottle of 104+ in a 944 provides a more preceptible boost than the bosch +4 plugs I had installed and any other minor mods I had made. Again, this is my own experience, it seems everyone else thinks it's BS, I respect their opinions...the 104+ didn't do **** in my boat but you can feel it in a 944.

It may clean you 944's engine particularly well for whatever reason, but I will guarantee that whatever boost you are feeling is from the detergents cleaning the system and not from any octane boost it might provide.

Let's put it this way, there are what, 12-20 ounces of 104+ in a bottle, right? A full tank in a 944 is just over 20 gallons (about 2,600 ounces).

To find out what the octane rating of pure 104+ would have to be to go from an overall tank rating of 92 octane to an overall tank rating of 93 octane, we can use the following formula: [(20*x)+(2,580*92)]/2,600 = 93

Solving for "x", we can see that the octane rating of pure 104+ would need to be 222.

If the octane rating of pure 104+ is actually 104 octane, then using that same equation we can see that adding a bottle of 104+ to your tank will raise the octane from 92 all the way up to 92.09. There is absolutely zero potential for an increase that insignificant to make a difference.

So to raise the octane rating of a tankful of gasoline by one single point, the octane rating of that bottle of 104+ would need to be more than twice the octane rating of the best, most expensive, racing fuel. We won't even begin to get into the astronomical octane ratings it would need to have to raise the octane to something like 100 or 103 (typical race fuel levels).

If you're feeling a difference in your 944, you've got something that's getting gummed-up somewhere and the 104+ is correcting that. But as I said, it pretty much scientifically impossible for the benefit to be coming from the miniscule increase in octane rating.

[AaronM]

Originally posted by Geo31
Octane is NOT a rating of how fast the fuel burns. It is a rating of resistance to auto-ignition. There is a difference. Higher octane does not mean slower burning.

Correct. However, higher octane does mean a lower per-unit-volume energy content.

And I believe that there have been some studies to show that the flame front travels marginally slower with higher octane, but the speed of the flame front doesn't have anything to do with how fast the burn occurs.

[HiFiGuy66]

Hi All,

Not really an octante question, but a related question nonetheless...

I'm waiting for my 944 to arrive from Arizona, and have been doing loads of research on the car so that I can care for it correctly.

I think we all agree that Porsche recommends 87 octane fuel for the 944 NA. However, I have also read that as motors age, a higher octane fuel is beneficial. Is this true? Do gasoline companies put more or better additives in Super Unleaded as opposed to the regular stuff? My concern here, of course is keeping the injectors clean.

The 2.5L engine in my 89 325is is notorious for building up crud on the back side of the intake valves, and I've been using name brand super unleaded for years, trying to keep the injectors cleaner (cleaner burning fuel.) Am I misguided here?

I have had the injectors cleaned at the Mobil Quick lube place. They run a tube directly to a vacuum line on the intake and drip cleaner into it, kind of like an automotive IV. I do notice a difference in idle quality and an increase in fuel ecomomy after I have this done (once a year.) The service is $59.

What do y'all think? It sure would be nice to save some money on gas, as the BMW gets a combuned 25/2 MPG city and Hwy. When the injectors get gummed up, fuel economy dops to 24.5 MPG. Is the fuel injector service and regular a good idea with a 944 wilth 128K on the odometer?

[GMingst]

Yes as motors age they can develop deposits in the combustion chamber that can lead to detonation. In these situations a higher octane fuel will help prevent that. BUT the days of accumulating alot of crap in the chambers really went away with the carburetor. Unless you are burning oil, the engine management in your car is so good that even after your mileage if you were to remove the head you would probably only see a light carbon coating at worst. Nothing really to cause pre-ignition. As far as cleaning injectors anything other than removing them and having them bench cleaned is a gamble as to whether it did any cleaning, or did even cleaning. The Mobil service you used does work, but you are guessing as to how effective it really was on the injectors. Your mileage may increase, but you could still have blocked, or a bad injector. Chances are yours are fine, as it sounds like you have kept up on the maintenance. If the 944 is laid up for the Winter it is not too difficult to remove the injectors and send them out for a cleaning. Cheap too, @ 10 - 15 per injector.

Regards
Graham

[Wolf1]

Originally posted by Ferrara_racing


A bottle of 104+ in a 944 provides a more preceptible boost than the bosch +4 plugs I had installed [/B]

This I believe.




Platinum plugs are not intended to be used a performance boost.

And the Bosch Platinum +4 is the most likely to actually affect driveability in a negative way.

Ever hear of indexing spark plugs? The Bosch plug is totally opposite of this, it is shrouded on four sides.