I just don't understand it. Why would MB make a V6 engine that consumes Premium fuel? My mom's Cadillac is a V8 with 320 horsepower, and takes regular. Why couldn't Mercedes pursue this path too? I don't get it...

 

Well I would say that it is because of the 10.5:1 compression ratio... You put crappy gas in you get predetonation and in turn you get timing pulled which creates less horsepower overall.

 

Because they make this a 10:1 high compression engine. The up side is that it creates more horse power on each explosion, but the down side is it cost more to the user, it require premium gas.

If you use lower octane gas on this engine, it may cause knocks. This pre-exlosion will cause damage to the engine because of the incorrect timing. However, this engine has knock sensors that will retard the timing of the engine and should run with no problem.

I'm actually trying a few tanks of regular gas on my car, I'll share the results over here later.

 

Some cars will get less mileage on regular gas so buying regular doesn't save you anything in the long run.

The major concern I have with using regular is the possibility of having warranty work denied. I don't doubt that the engines will run just fine on regular - even in the SRT6. But I would also not be surprised if the ECU records the timing retardation to account for the lower octane, and Chrysler using this as a reason to deny warranty coverage because the car was not operated as intended per the Owner's Manual.

 

Because its not a Caddy

 

Its A "Premium" engine!
There have been several unofficial forum tests (i tried it twice to see) and the difference in MPG (lower for regular) makes it a push dollar wise, like using synthetic oil vs regular oil with the extended life of the synthetic making the price the same so why the complaint on either one. Use whatever you want but your performance and reliability will probably suffer for zero net savings.
Just MHO and $.02.

 

I have been using the in between grade for six mos and not having a problem

 

The way I look at it is... yesterday I filled up 12.789 gallons at the price of $3.129 for premium, to a total of $40.02. Now lets say I had filled up the same amount at the price of $2.852 for regular, to a total of $36.47. Looking at it from this perspective the difference in price is so marginal that I definitely choose to purchase higher octane gasoline. I am a college student and thrifty when I can be, but this is just an example of weighing the pros and cons. Pay $4 and get better mpg, smoother performance (in my opinion), and peace of mind your engine has what it needs.

 

Because in Europe they use better quality fuel, thats why most European cars need to use at least 95RON, or 91 in US.
From Wikipedia
In most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in the United States, Canada and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 8 to 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, would be 91-92 in Europe. However most European pumps deliver 95 (RON) as "regular", equivalent to 90-91 US (R+M)/2, and even deliver 98 (RON) or 100 (RON).

 

The simple fact is that the 3.2L engine "requires" premium fuel to obtain maximum performance. It will not make as much HP at full throttle with less than 90 (R+M)/2 octane fuel.

Contrary to what some have said on this site, the NA Crossfire's 10:1 compression ratio is not a high compression engine by today's standards. Many other vehicles with comparable compression ratios run just fine on regular gasoline. My daily driver is a 2.2L 04 Olds Alero (no laughing please) and it has a 10:1 compression ratio. We also have an 01 V6 Ford Escape that is 10:1. The Ford Escape Hybrid has a 12.3:1 compression ratio and it still requires just regular unleaded! So, the answer is obviously more complicated than just compression ratio. Valve timing profiles, engine materials, configuration and operating temperatures greatly influence the combustion process as well.

Here's a good article on regular vs. premium from a few years back:

http://www.usatoday.com/money/autos/...emiumgas_x.htm