Question on Octane Used on my Wife's Car

[TheWatchGuy]

Originally Posted by JamesNoBrakes

I think in general ECUs limit the car to the rated/designed HP. This means when you put higher octane in, it "doesn't care". It doesn't try to do anything with this at all. If you have a tune, and especially if you have a turbo, you can take advantage of this, but otherwise, it just "doesn't care". The cams won't support more power and it just doesn't care.

The whole thing about "higher octane doesn't benefit" is limited to those lower performance cars and the people that buy high octane for them. My Hyundai Elantra GT N-line was specifically designed to give max performance on "regular". A little 200hp 1.6 turbo-4. With a tune and a couple mods like wastegate solenoid and boost control solenoid, I was running it on premium and it ran well, but then I was asking a little more out of it than stock. Stock, it didn't care if I put premium in or not, that's how they designed it. Cars like my SS 1LE or Stinger, they crave pretty high octane. Lower octane makes a noticeable difference.

I'd be surprised if there was more than a 5% decrease in power on 87 vs 91/93

On your stinger, have you logged 87 vs premium stock? Cause I've logged my g70 and stock, there's not a huge difference in timing/ boost. Haven't had it on the dyno to say for sure yet though. With a tune, yes it will be noticeable. I suspect it would be more noticeable with cars that have more aggressive stock tuning. The 3.3tt in the stinger and g70 is pretty de-tuned stock.

[chris719]

It really depends on the engine. I would not want to be the guy running 87 in a BMW S65 or S85 lol.

[TheWatchGuy]

Originally Posted by chris719

It really depends on the engine. I would not want to be the guy running 87 in a BMW S65 or S85 lol.

it may run rough initially as the ecu adjusts, but BMW is pretty good with having their ECUs adjust for fueling.

i dont see why someone wouldnt run premium, especially with how many places add cleaners to their premium fuel, but it wont do any damage in a modern engine. S85 might be different though, since that engine shits the bed even if you give it top tier fuel and baby it.

[F32Fleet]

Originally Posted by jpy1980

So I leased my wife a 2019 Audi Q7 3.0T back in 2019 for a 3 year period.

Now for all of MY cars, I treat them better than my first born, but since this was a lease and we decided we would definitely re-lease a new car at the end, I decided to use 87 octane instead of the recommended 91 octane. I know, I know. Bad bad cheap me. BUT now that the car has served us so well, my wife wants to keep it. UGH. The car drives fine and I have followed the maintenance schedule, but have I done any real harm? How could I check and see if it's worth keeping? I'm usually the type of person that even treats rental cars well, but with this car I just didn't think it was worth it since we weren't going to keep it.

Thoughts?

Unless Audi states an absolute minimum octane you're fine.

[The Libertine]

Originally Posted by KennyFSU

The ecu just compensated for the lower octane so I'd assume it didn't cause any damage but who knows long-term. If there haven't been any CEL then I'd say it's fine.

Talk about karma biting you back in the ass lol.

I agree. Might as well make the switch to the higher octane now!

[Fritzer]

The only issue I can really see arising from this is extra carbon build up and more wear on the fuel system as a whole. You just have a dirtier fuel system is all. The engine certainly identified the lower octane and adjusted accordingly, there should be no issues in terms of that. Using 93 will clean the fuel system slowly, maybe use a Liqui Moly fuel system additive which has additional powerful detergents.