MyDogWally

Thinking of buying an A5 for my wife, but I'm a bit put off by Audi's recommendation of premium gas. Just wondering if I can use a lower grade of gas and, if I do, will I suffer any performance or MPG issues?

findalex

YES, use premium. The A5 uses a high compression turbo, so a high octane gas is required.

If you want to save money on cheap gas, get a Toyota.

KBoltz

High compression engines (especially turbo charged ones) absolutely require higher octane gas to keep from getting knock and pre-detonation issues.

Doesn't matter what manufacturer you buy from, I owned a Corvette and had long tube headers, full intake and exhaust mods and a tune from EFI Alchemy in Jacksonville. Premium fuel was a necessity. When I ran her at autocrosses or HPDE's I got the highest octane fuel I could.

My 2015 Cadillac ATS had to run premium as well, the one time I had no choice but to run regular (I lived way out in the sticks, and they had not gotten the tanker truck with premium) it ran like ****. I lost almost 7 MPG, and acceleration was crap was well. I added octane boost to try and alleviate the problem, it helped, marginally. As soon as I got down to half a tank, I filled up with Premium.

There is a reason that manufacturers recommend the fuel they do.

If you are put off by using premium, go with a car designed for a lower grade of fuel. Y

MyDogWally

Thank you both very much. I appreciate the replies.

leifmb

Most people either don't "believe in" or want to pay for High Octane gasoline, or simply think its a scam somehow! Well, it's not. Higher compression and usually higher performance engines are tuned for high octane fuel and if you use the mid or low grade fuels, the engine should run but the Powertrain control module for the engine (primarily) will "retard" the (spark) timing to compensate. The computer knows to do this by several factors but the primary one is the engine "knock" sensors. The "knock" sound comes from the air-fuel mixture in the compressing cylinder, igniting too soon, causing the piston to want to travel down while its still going up! The computer literally hears this condition and keeps retarding/backing off the timing until the knocking is no longer "heard" or it reaches it maximum timing (redard) setting. Driving the engine with sub-standard (low octane) fuel for that engine spec can cause the pistons to become damaged as well as other rotating surfaces and eventually lead to engine failure. However, if you do use lower octane fuel, AND you drive very light pedaled AND the engine is running cool (helps), AND you don't hear any knocking, I would think you would be just fine to drive. I just wouldn't make a habit out of it. Sometimes however, and depending on the factory tuning parameters of the vehicle, there is a little more leeway and you can use the next grade fuel down with little problems, as long as the timing variance needed is capable within the adjustment available to the computer! But again, prob not the best idea to make a habit out of it as the computer can "hear" knocks you cant...big brother is listening to those knocks. The question is, what are you going to do about it? lol

Leif

uberwgn

Wally: T O Y O T A

harveylove

Definitely due to the high compression

Neil L F

As indicated it is the high compression and forced induction (turbo, supercharged). Octane level is an indicator of a fuels ability to ignite. Higher octane has a greater resistance. If a lower octane is used predetonation can occur when the piston is too early on the upstroke causing damage to the engine. Higher compression also results in higher temps which can also cause fuel to ignite too early. You can used 91-93.

Fithian

Sure, you can use any grade of gas that you want. The engine management system will take care of the possible knocking problem. You will get slightly lower MPG and performance, not linearly with the reduction in price for regular fuel. That said, I always get 93 octane (91 W of Mississippi) when I fill up. I won't be using any gas in my next car.