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Use 91 at worst in my 2018 RS5. 93 everytime I see a station offering it. Getting about 21.5 mpg on first 3500 miles. Too early to tell re gas & performance, but I would certainly agree with those owners using 93 if available. 91-$3.08/gallon and 93-$3.16/gallon in KC. $1.20 diff for a full 15 gallon tankful.
A higher Octane rating does not mean more power. That's what gasoline companies make us think it does. A higher Octane rating just means that the duel, when compressed based a certain ratio, does not detonate prematurely. If the car manufacturer recommends 91 Octane, you are just wasting good money on 93 for no gain. Your car's engine was designed to perform optimally on 91 Octane. Just use 91. In the event you find your car low on gas in a place with no 91 or 93 octane, then filling up with 87 or 89 is also OK because the engine has the ability to retard timing and adjust itself to the lower octane fuel.
That is fundamentally true, however, there's a twist to this when it comes to European cars. If you've ever done European Delivery or driven in Europe you'll know that these very same cars require 98 RON over there, which is equivalent to our 93. In fact, and that's where it gets interesting, when I picked up my RS5 in Ingolstadt 5 years ago it had a different sticker that said 98 RON. Then when I reclaimed the car here in CA, the sticker had been changed to the 91 (95 RON). I specifically remember this, because I was wondering when I saw the 98 RON sticker after picking up the car, knowing that I can't get anything above 91 (95 RON) back home in CA. 95 RON is midgrade in Europe. So the question now is did Audi detune the engine when the car got here to run optimally on 91 or do they just leave it up to the ECU to sort it out. Either way, in theory both would result in a slight loss of power that could be regained by filling it with 93. I never felt a difference, but I'm pretty sure that the potential loss of power due to the lower grade was probably offset by the gain in power living at sea level vs the higher altitude on average in Europe, although I did visit places at sea level as well. While in Germany, I mostly filled up with BP Ultimate 102 Octane, which was readily available. I figured since I was actually hitting the top speed of 174 mph regularly I might as well fill it with the best available.
Last edited by superswiss; 07-11-2018 at 12:54 PM.
My guess is that Audi left the ECU the way it is and the engine is indeed tune for 98 RON. That would explain why most Audi in the US seems under rated power wise. I have owe a few cars with 400+ HP and this S5 feels faster.
I agree. Realistically, why wouldn't they leave it tuned for 93?
Half of the US gets 93 gas always (half by population, that is) and the car is fully capable of adjusting on the fly for lower octane gas with no ill effects.
As others have said, probably dependent on where you live, but I use 93 octane since I've never seen 91 here, and I only buy from Top Tier approved brands. https://www.toptiergas.com/licensed-brands/
Seems to be a big love affair with Shell, but I don't like that the ones near me play the game of the prices for regular unleaded being the same as the BP across the street, but premium is often more than 20 cents higher at Shell vs BP.
07-11-2018, 07:06 AM
