[Hunter399]

Costco 93

[ACF90M5]

Shell 93 only unless I absolutely need gas. The extra cost is worth it for piece of mind imo, especially for engine longevity. When I had an oil issue with my last car a tech from Germany had to look at it and, despite having 50,000+ miles, told my advisor that the engine was "immaculate and looked like new." I attribute that directly to the 93 VPower formula (even though I guess 50,000 isn't a lot of miles but to me it is).

https://www.toptiergas.com/licensed-brands/
Here is the link for anyone who needs the Top Tier list. Sunoco just met their standards early last year I believe as I know it was not on there before.

[Pimpsy]

Originally Posted by ACF90M5

Shell 93 only unless I absolutely need gas. The extra cost is worth it for piece of mind imo, especially for engine longevity. When I had an oil issue with my last car a tech from Germany had to look at it and, despite having 50,000+ miles, told my advisor that the engine was "immaculate and looked like new." I attribute that directly to the 93 VPower formula (even though I guess 50,000 isn't a lot of miles but to me it is).

https://www.toptiergas.com/licensed-brands/
Here is the link for anyone who needs the Top Tier list. Sunoco just met their standards early last year I believe as I know it was not on there before.

Shell 93 for me also. Dependably high quality.

[devondragon]

I'm in CO and 91 is the only thing available, but I normal augment with Royal Purple octane booster (did some research and it seemed like the best one). But am open to other recommendations.

[btsmith]

Costco 93 for me!

[wanesso]

Just started using 91 no-ethanol, which is available in limited way in the northeast though at high price, and notice actual improvement in mileage in my GTR. Haven't driven the M5 yet as I await snow tires but I'll try it there too. When it's not available, I use the 93....

[JOHNBMWM5]

Here in the UK I use TESCO 99 or Sainsbury 97, car loves it, shell complete rip-off, never touch it.
Tesco and Sainsbury £1.26p/Litre
Shell £1.45/Litre for 98

[F90M5C]

Shell V Power 98 here at home and Aral Ultimate 102 when im in Germany .

[vtknight]

There is a great deal of misinformation when it comes to octane levels North America vs Europe ratings and especially ethanol. Once you go the performance path - specifically FI vs NA - it is good to know your fuel.

The negatives to ethanol enriched fuels is not - in my opinion - what people think. Because most people think damage to their engines. The good news is we are not bikes or boats - or in our case cars pre-2001. The real issue with ethanol added fuels is stability of rating. Batches of fuel can vary. Pure octane rated fuel is superior here. Ethanol also evaporates quicker and you need more volume which means less MPG - although ethanol is usually cheaper.

That said - there is a reason why almost all new FI builds are using E85 or E98 (or their numbers in between). Ethanol doesn’t produce its power from octane rating alone - it is actually lower than straight race fuel in that regard. What it DOES do is two things: cools and via an increased fuel volume - decreases detonation due to an improved fuel vaporization - about 3 times that of regular octane. This creates a cooler charge temp - which combined with the octane of ethanol (which is 113 octane) reduces the chance for knock and increases power. You can expect about a 30-40% increase in fuel demand to achieve this (based on your builds power/boost levels).

As an example - the car I race used Q16 race fuel. An oxygenated 116 octane fuel. Using E98 - I made an additional 200 awhp because the fuel allowed more timing and boost. That said - that build drank 3 gallons of fuel for one 1/4 mile pass. But - I’m not using fuel octane to save money. It’s about saving my engine and performance.

So - for me personally - I used the highest octane I can - always. Pure 93 is great - and is my first choice for a regular stock car because it is the most stable. 94 if I know the batch is solid - because of the above points (113 octane added - as 10% of the fuel typically kicks up the overall octane level two points - so base 94 is usually 92 octane - so it’s a win win). For 93 with 10% octane - that would mean the base is 91 - which with a bad batch is crappy. I never put 91 RON/MON into my car (I know it’s all you have in Cali and that sucks).

Lots of good reading on the subject - I will be back with a link or two.