karasha

iTrader: (5)

The Shells down in my area are just outrageous when it comes to price... and I've always filled up 93 at Chevron and no complaints at all.

Byprodrive

iTrader: (1)

When I worked at Shelby American I took a Series 1 to the GM Proving grounds in AZ for emissions compliance development, the engineer in charge said to be sure & fill the tank with Chevron Premium 91 octane minimum. This was in 1998.

isFiend

Very interesting responses; thank you all for your time.

Seems like one can't go wrong with Chevron premium, although again like I said I'm still not truly convinced that there's anything subpar about Shell (most of these responses claim that while both Chevron and Shell meet the national standards for detergent amount, Chevron adds more).

IS-SV

I use nothing but Chevron premium (91) in California, no problems.

rebs

I'm going to add my 2 cents on this topic (and probably regret it).

One poster said that all gasoline has to meet federal guidelines for detergent. That is true, but that low standard (because the feds were reluctant to alienate anyone in the oil industry) was originally set almost 15 years ago.

Top Tier gas is more then a marketing gimmick. Top Tier Detergent Gasoline standard(s) was actually started in 2004 by BMW, General Motors, Honda, and Toyota. These car manufacturers are generally in competition with one another, and you'll also notice that the gas/oil industries that have made the list generally compete with one another as well, so it's a little more than a conspiracy or marketing gimmick.

Now having said that, a lot of gasoline is the same (and often may come out of the same pipeline), but the additives are usually different. Now, whether or not those additives are effective (or more or less effective than a different companies additives) can definitely be debated. I've often seen conflicting information/results when independent labs are involved, and I'm not 100% convinced of many of the additives out there.

However, I would be reluctant to completely discount Top Tier gas. There is some good information about some of their requirements here: http://www.toptiergas.com/deposit_control.html

Although, I'm a penny-pincher to a certain extent, I've had some bad (diagnosed) experiences with some cheap gas and also know of people (friends, co-workers) that have as well, so I usually utilize a top-tier gas at a *reputable* station (the peace of mind on this fairly expensive vehicle is worth the extra $2-$3/tank).

Personally, I generally use Chevron or Shell, but despite the comments on here I haven't really noticed a difference yet.

...and that's my 2 cents.

Koz

Shell and Chevron both meet the Top Tier standards in detergents additives which far exceed the EPA's standards. These are the top tier standards;

1.1 Retail Gasoline Performance Standards. The deposit control performance of unleaded gasoline conforming to section 1 of this document shall be met at the retail level in all grades of gasoline sold by a fuel company in all marketing areas of a selected nation. In addition, conformance to the standards shall mean gasoline sold in the selected nation shall not contain metallic additives, including methylcyclopentadienyl manganese tricarbonyl (MMT).

1.2 Deposit Control Additive Requirements. The deposit control additive used to meet the performance Standards described in 1.3 shall meet the substantially similar definition under Section 211(f) of the Clean Air Act. Also, the additive shall be certified to have met the minimum deposit control requirements established by the U.S. Environmental Protection Agency (EPA) in 40 CFR Part 80. Lastly, the additive shall be registered with the EPA in accordance with 40 CFR Part 79.

1.3 Deposit Control Initial Performance Standards. Initial deposit control performance shall be demonstrated using the tests shown below.

1.3.1 Intake Valve Keep Clean Initial Performance Standard.

1.3.1.1 Test Method. Intake valve deposit (IVD) keep clean performance shall be demonstrated using ASTM D 6201, Standard Test Method for Dynamometer Evaluation of Unleaded Spark-lgnition Engine Fuel for Intake Valve Deposit Formation. Tests demonstrating base fuel minimum deposit level (1.3.1.2) and additive performance (1.3.1.3) shall be conducted using the same engine block and cylinder head. All results shall be derived from operationally valid tests in accordance with the test validation criteria of ASTM D 6201. IVD results shall be reported for individual valves and as an average of all valves.

1.3.1.2 Base Fuel. The base fuel shall conform to ASTM D 4814 and shall contain commercial fuel grade ethanol conforming to ASTM D 4806. All gasoline blend stocks used to formulate the base fuel shall be representative of normal U.S. refinery operations and shall be derived from conversion units downstream of distillation. Butanes and pentanes are allowed for vapor pressure adjustment. The use of chemical streams is prohibited. The base fuel shall have the following specific properties after the addition of ethanol:

Contain enough denatured ethanol such that the actual ethanol content is no less than 8.0 and no more than 10.0 volume percent.
Contain no less than 8 volume percent olefins. At least 75% of the olefins shall be derived from FCC gasoline as defined by CARB (advisory letter, April 19, 2001).
Contain no less than 28 volume percent aromatics.
Contain no less than 48 mg/kg sulfur. At least 60% of the sulfur shall be derived from FCC blend stock.
Produce a 90% evaporation distillation temperature no less than 290°F.
Produce IVD no less than 500 mg averaged over all intake valves.

1.3.1.3 Demonstration of Performance. The base fuel from 1.3.1.2 shall contain enough deposit control additive such the IVD is no more than 50 mg averaged over all intake valves. Results for individual valves and an average shall be reported. The unwashed gum level of the fuel containing deposit control additive shall be determined according to ASTM D 381 and reported.

1.3.2 Combustion Chamber Deposit Initial Performance Standard.

1.3.2.1 Test Method. Combustion chamber deposits (CCD) shall be collected and weighed along with IVD using ASTM D 6201, Standard Test Method for Dynamometer Evaluation of Unleaded Spark-Ignition Engine Fuel for Intake Valve Deposit Formation. ASTM D 6201 does not contain a procedure for collecting and measuring CCD. Adapting a scrape and weigh procedure developed by CARB is recommended (see referenced test method dated March 12, 1999). Results for individual cylinders and an average shall be reported.

1.3.2.2 Base Fuel. Combustion chamber deposits shall be measured for the base fuel from 1.3.1.2.

1.3.2.3 Demonstration of Performance. The base fuel from 1.3.1.2 treated with additive at the concentration meeting the standard found in 1.3.1.3 shall not result in more than 140% of the average CCD weight for the base fuel without additive.

1.3.3 Fuel Injector Fouling Initial Performance Standard.

1.3.3.1 Test Method. Fuel injector fouling shall be measured using the TOP TIER fuel injector fouling vehicle test available from GM. GM will run the test on a first-come-first-served basis and shall make the method available to those who wish to run the test on their own.

1.3.3.2 Base Fuel. Two options for base fuel are available:

1.3.3.2.1 Option 1. A full boiling range hydrocarbon gasoline or gasoline blending component, without oxygenates and without deposit control additives, that results in at least five inoperative injectors when tested by the method in 1.3.3.1.

1.3.3.2.2 Option 2. Federal emissions test gasoline specified in DFR 86.113-04, into which 4-methylbenzenethiol (WARNING: Flammable solid; irritant) has been blended at a concentration of 56 mg/L. The blended fuel must result in at least four inoperative injectors when tested by the method in 1.3.3.1. the Federal emissions gasoline, without deposit control additives, available from Haltermann Products (1201 South Sheldon Road, Channelview, TX 77530; tel.: 800-969-2542) has been found to be satisfactory.

1.3.3.3 Demonstration of Performance. A demonstration of injector fouling shall be done first. At least five out of six injectors (with Option 1) or at least four out of six injectors (with Option 2) shall be inoperative for the test to be valid. A demonstration of additive performance shall be done after the fouling tendency demonstration; no other test shall be conducted on the vehicle in the interim. A demonstration of additive performance shall be conducted using the same vehicle (including the fuel drain and flush procedures and installing new injectors) with the same batch of base fuel, but now containing the same amount of deposit control additive as in 1.3.1.3. A pass is defined as no more than one inoperative injector.

1.3.4 Determination of Deposit Control Additive Performance Concentration.

1.3.4.1 Methodology. The concentration of deposit control additive needed to meet the standards in 1.3.1.3 and 1.3.3.3 should be equivalent. However, if the concentration of deposit control additive in 1.3.3.3 is grater than in 1.3.1.3m the higher value shall be regarded as meeting both standards. Also, if the difference between the two concentrations is grater than 15%, 1.3.2.3 shall be repeated using the higher concentration.

1.3.5 Intake Valve Sticking Initial Performance Standard.

1.3.5.1 Test Method. Intake valve sticking tendency shall be determined using either the 1.9 L Volkswagen engine (Wasserboxer according to CEC F-16-T-96) or the 5.0 L 1990-95 General Motors V-8 engine (SWRI IVS test). Two options are available for demonstrating intake valve sticking tendency.

1.3.5.2 Option 1. The valve-sticking tendency of the test fuel by itself will not have to be demonstrated prior to testing the candidate additive. The following shall be required of all tests:

Test fuel shall be either the same as in 1.3.1.2 or CEC valve sticking reference fuel.
Concentration of deposit control additive in the test fuel shall be at least twice the amount determined in 1.3.4.1.
Test temperature shall be -20°C.
Three 16-hr cold soak cycles, each followed by a compression pressure check, shall constitute a complete test.

1.3.5.2.1 Demonstration of Performance. A pass shall result in no stuck valves during any of the three cold starts. A stuck valve is defined as one in which the cylinder pressure is less than 80% of the normal average cylinder compression pressure.

1.3.5.3 Option 2. The valve-sticking tendency of the test fuel together with an additive known to cause valve sticking shall be demonstrated prior to testing the candidate additive. The following shall be required of all tests:

Test fuel shall be either the same as in 1.3.1.2 or CEC valve sticking test reference fuel.
An additive known to cause valve sticking shall be selected, and, when blended into test fuel, shall demonstrate valve sticking tendency as follows: (a) for the Volkswagen engine, at least two valves shall be stuck; (b) for the GM engine, at least three valves shall be stuck.
Test demonstrating performance of the candidate additive shall be conducted at a concentration that is at least three times the amount determined in

1.3.4.1.
Test temperature shall be -20°C.
One 16-hr cold soak cycle followed by a compression pressure check shall constitute a complete test.

1.3.5.3.1 Demonstration of Performance. A pass shall result in no stuck valves during the cold start. A stuck valve is defined as one in which cylinder compression is less than 80% of the normal average cylinder compression pressure.

As you can see the standards and testing is very specific.

Koz

Eldr1dgE

Interesting...here in san antonio our octane levels are 87 reg, 89 plus, 93 prem...so basically i fill up premium all the time...i also use chevron or shell...i also think you should stick to one brand of gas because each brand has there own types of additives...i know it probably doesn't matter but i do feel a little difference when i switch up brands during the month..it's probably just me but i think the engine senses when i switch from chevron to shell..

kickin8

iTrader: (1)

anything above 91 would be fine.....

isFiend

Sounds good guys. I just filled up on 93 premium Chevron and everything seems to be in great order. I'll go ahead and make Chevron my gas of choice just to stay consistent.

GiantsFan

iTrader: (9)

man... no 93 where i am in CA .... only 91

juice14

I get the most expensive one no matter what. lol

Kurtz

iTrader: (1)

For a car that requires 91 (like the 2IS) there'll be no difference whatsoever between 91 and 93. Higher-than-needed octane doesn't do anything for you (except waste money in the case of say a car that only requires 87 but some guy keeps putting in 90-something anyway thinking it's "better")

What a station calls premium can vary between 91, 92, 93, and 94 octane depending on your state (or sometimes even within a state)

Byprodrive

iTrader: (1)

You don't think a IS350 will dial in more timing advance for 93 over 91?

I drove mine crosscountry when I first got it & it SEEMED to respond to Ammoco 93 which I got instead of my usual Chevron 91

Koz

For as often as the timing is retarded there is no need to use higher (then 91) octane (expensive just in case). You will hear the knock if the system can't retard the timing enough. Each State/climate/altitude has different formulated gas.

Koz

GQD_GS4

+1...strange but true on my rx400h