Recommended brand of gas for 550

I've been using whatever's available. There's a Chevron really close by, so generally I'll use that. We're paying out the nsoe here for 91 (2.43 I think), but whatever. Cheaper than crack (100 octane, on the other hand, makes the white stuff look cheap ).

One thing I've noticed that helps the car, and is battle tested (by some ferraristi, including one guy who uses it every tank in his insanely-fast, highly modded f40, did in his 100k+ miles TR, etc) is Swepco 503. It's a fuel improver / gunk remover that is (I think) ~$6 / bottle. I'll throw it in every couple of tanks (err, so twice a day ), and while there's no night-and-day difference, the car does seem to be a little smoother in general. Also, I don't get nearly as much 'idle flutter' at start-up (not that there's much, but you get the idea).

Unless you've got a directly line to good gas for cheap (Sears Point has 92 for $1.87, and 100 for $3 instead of the usual 5!!), go with what you know.

--Dan

 

By the way, that 97 is measured differently. 91 is the US equivalent (and minimum).

--Dan

 

850CSI - one of the single greatest cars to ever come from BMW.

I'll check my manual tomorrow to see what it says, just for kicks.

--Dan

 

Here's a summary that includes just about everything you'd ever want to know about octane, including the two different ways of measuring it.
(It's my opinion that the brand of gasoline is completely irrelevent.)

In addition to the many additives present in gas, such as, dyes, detergents, and alcohols, gases are also distinguishable by their grade. The grade of gasoline is usually specified by an octane rating number. The octane number is a standard laboratory measure of a fuel's ability to resist knock during combustoin in a spark - ignition engine. "Knock" is a harassing trait in engines that is linked to gasoline, characterized by a ping in the motor during operation that results in loss of power, mileage, and smoothness of engine performance. It is caused due to the ignition of some of the hydrocarbons that compose the gasoline by the high temperatures and pressure conditions inside of the engine cylinder before it is ignited by the spark plugs. A single - cylinder four - stroke engine of standardized design is used to determine the knock resistance of a given fuel by comparing it with that of primary reference fuels composed of varying proportions of two pure hydrocarbons, one very high in knock resistance and the other very low. A highly knock - resistant isooctane (2,2,4 - trimethylpentane, C8H18) is assigned a rating of 100 on the scale and normal heptane (C7H16), with a very poor knock - resistance, represents zero on the scale. Octane number is defined as the percentage of isooctane required in a blend with normal heptane to match the knocking behavior of the gasoline being tested.

The CFR (Cooperative Fuel Research) knock - test engine used to determine octane number has a compression ratio that can be varied at will and a knockmeter to register knock intensity. In the classic method of knock rating, the engine is run on the fuel to be tested, and its compression ration is adjusted to give a standard level of knock intensity. Without changing the compression ration, this knock level is then bracketed by running the engine on the primary reference fuel blends, one of which knocks a little more than the test fuel, and the other a little less. The octane number of the fuel being rated is then determined by interpolation from the knockmeter readings of the bracketing reference fuels.

Alternatively, the engine's compression ration can be adjusted to close to the limit for the fuel being tested, and then, while the engine is run on each of two closely bracketing test fuels, the ratio can be readjusted to a standard intensity reading on the knockmeter. Finally, the engine is again run on the test fuel, and its compression ratio is adjusted to give the same knockmeter reading. The octane number of the test fuel is then interpolated from the compression ratio settings.

Knock tests are performed under one of two sets of engine operating conditions. The Motor method (M) is designed to correlate well with the fuels and automobile engines of the 1930's, the time when this method was developed. The other method, called the Research method (R), was created later and was better suited to rate the gasolines that were made from the improved refining processes and engines gave gasolines better road performance than their M ratings indicated. Today, the arithmetic average of a gasoline's R and M rating usually is a good indicator of its performance in a typical car on the road. Thus, that average, (R+M)/2, is posted at service stations to show the antiknock quality of a fuel. Look at your gas pump and this equation is often shown on the front.

For fuels with a rating higher than 100 octane, the rating is usually obtained by determining the amount of tetraethyllead compound that needs to be added to pure isooctane to match the knock resistance of the test fuel. For example, if the amount is 1.3ml, the fuel's rating is expressed as 100 + 1.3 or extrapolated above 100 (in this case, about 110 octane) by means of a correlation curve.

The octane number of a gasoline can be increased by the use of reforming techniques and by alkylation, where gasoline components are recombined to build a larger molecule with a high octane number.

 

Sounds great, but this is what tax law must look like to most folks. Are you saying that premium is worth it due to the additional additives. Or, are you saying the opposite.

Thx, DrTax

 

Neither.

 

Then are you saying that I should try the cheapest gas I can find until that ole lump starts a knocking?

 

I have a friend that is a Jobber ( gas wholesaler ) He always runs Texaco, I run Shell or Texaco.

It is not a stretch to say you are what you eat or in this case your car is what you feed her.

There is alot to a tank of gas. Anti knock anti corrosion, who knows what all is in a gallon of gas. With all the aluminum and other alloys be carful of running cheap gas you could wind up spending way more on tune ups and overhauls. On the farm we get some pretty crappy gas from the local Co-op that due to their storage has water in it. Fine for a truck but not my F-car.

He also stated that when he pulls up to the huge gasoline storage tank in Portland he pulls from the top and pays a premium to do so. ARCO trucks pull from the bottom of the tank. Guess what you get when you go to ARCO to fuel up. The worst gas you can buy. Yes maybe here in Salem we get our gas from a pipe direct from Seattle refineriers. But how you ship and store and even mix makes a diff.