I have concluded experimentally that my '05 Limited Couple was octane and air limited.

Replaced the air box with the MB V8 one with K&N filters, big improvement in throttle response, esp. at low to mid revs.

I'm in Phoenix, 91 octane premium sucks 'cuz of the air pollution-required stuff they do to it. By "splash blending" with 100 octane unleaded racing gas ($4.65 a gallon) I find that at 93 or so octane everything smoothes out remarkably - acceleration is continuous thru the rev range, sudden throttle openings at mid-revs are much smoother. Even my gf said something about how it felt, and when I had one of our race drivers drive it, he said I had made major improvements - thought I'd changed the computer !!!

I have now tried the 91 octane gas with 104OctaneBoost (one of the better octane boosters, and it didn't harm my Audi Sport Quattro or other German cars in extended use), and have the same results. BTW, I use either Techron or Shell gas here, seem to be the best and most consistent, not the cheap sh*t.

Tazz

 

You are correct in your conclusion... And here's probably why... Per the Bosch MotorSports Rep., the knock sensors on this engine are VERY sensitive, any hint of knock, or even the sound of valves clicking will cause the ECU to retard the timing and fueling. Even if you can't hear anything the knock sensors can. Also, since our engine runs dual plugs which are rated on the "HOT" end, the engine is prone to a minor amount of pre-ignition, that's why they recommend 91 or higher octane fuel...

So by increasing your octane level you are preventing pre-ignition thus allowing the ECU to run your engine without reduced LTFT STFT and retarded timing...

It was recommend to me that I should use a isolation spacer between the knock sensors and the engine block to prevent the sensor from detecting certain valve tick and minor knock... I'm going to build one that will work on our car since none exist in the aftermarket...

You also might want to try a small amount of MMO in your fuel... It will help lubricate the valve seats and prevent varnish build-up like you have seen on my other posts...

 

PS: Don't waste your money on octane boosters... Use Toluene... I have mixing ratios in other posts...

 

MMO?

Please spell out what this is for those of us not familiar with the acronym.

Thanks!

 

Marvel Mystery Oil

 

Just an added comment to gasoline brands.

In the USA most gasoline is piped to the distribution center from the different refineries using the same pipeline. Shell gasoline mixed with Mobil, mixed with Arco, mixed with independent brands.

The gas companies "Sell" the gas to the pipeline company and then "Buy" it back at the distribution center (Called Batching). If you observe the distribution center you will see that trucks (jobbers) from all Gas Companies and Independent dealers all get their refined gasoline from the same source (the rack). How would they know when Shell gas comes out the spicket (rack) VS Arco gas? They can't, it would not be efficient. Thus Gasoline is a commodity sold on the open market (spot).

The lesson is, unless the fuel comes straight from the refinery (trucked), there is no difference in fuel quality between brands, unless the gas station has leaky or contaminated tanks. And all gasoline is refined to a federal specification, with the specs are different for each region of the US. Western States have less sulfur requirements among other things.

One of my MBA teachers worked for Atlantic Richfield (now ARCO) for 20 years in the pipeline business. I could go on about how gas companies use this to inflate profits.

BTW - Pipeline delivery is very efficient, this why Ethanol fuel is a bad choice for our future. Gasoline and water don't blend and can be separated at the distribution center with a fuel/water filter or separator. Ethanol and water do blend (and this happens in the pipeline) and cannot be separated, thus creating a diluted fuel product.

Here are some links but you can google and learn more.

http://vettenet.org/octane.html

This link is great and a must read but as a pilot and aircraft owner, I disagree with the last sentence, empty fuel tanks allows water to condense water bad in planes, make engine stop, not good when airborne.

http://www.ftc.gov/ftc/oilgas/archive/061212.htm
http://www.eia.doe.gov/bookshelf/bro...05primerM.html

 

All true, except the premium is often diluted/mixed with cheaper gas by some distributors or stations, there is often a noticeable difference when I go to the cheapo station in a car that is more octane sensitive...

Tazz

 

Don't forget about all the Additives that different brands claim, such as Tecron, and other detergents and modifiers. When are those added? It would be false advertising if those additives aren't actually there. Further explanation on that issue would be appreciated. I think these additives and variations are the primary reason that people seem to be able to tell a difference between brands. I don't think it's all in our heads...

 

If this is true - report the station to the proper state authority. There should be a sticker on the pump with a number to call.

All Gasoline, regardless of "Brand" will provide the same performance in your car. Only differences being the Octane Level. Additives do not effect performance. That is unless the gasoline is diluted or contaminated.

Everything else is a marketing gimmick.