FO2K

Not "Bling Bling". but "Ping Ping".

slalom44

By design, our engine has high compression. High octane gasoline burns slower and is less prone to predetonation, especially when the compression is high and the fuel mixture is rich (like when you are accelerating heavily). If you use a low octane fuel, your engine will predetonate, or "knock". The knock sensors will pick this up and retard your timing to eliminate the problem.

But retarded timing has consequences. It robs your car of horsepower and efficiency. But it does not do any damage to your engine. Contrary to popular belief, running on low-octane gasoline is not harmful to your engine as long as you knock sensor is operational. It also does not void your warranty. But it would not be surprising if your car seemed sluggish when you used low octane gasoline.

If you use an octane rating higher than is designed (and recommended) for the car, you are just wasting money. A 93 octane gas doesn't do anything that a 91 gas will do. A cushion against knocking is of no benefit to the engine.

When I go on a long trip and I'm going to burn an entire tank of gas getting soemwhere, I use 87 octane fuel. I'm not doing any heavy accelerating, and the knock sensor isn't retarding the timing. And I ususally get my best mileage using low octane fuel on these trips.

tritium_pie

good info! thx. I'll have to try this the next time I know I'm going to be going on a long trip. I might just go down to 89 though. in the end, it's only a difference of maybe a buck.

I'm curious about the science behind mileage gains from a lower octane fuel. could it just be that since you know you have only 89 in the tank, that you drive extra conservatively, and thus your mileage gains are actually a result of your modified driving style?

alexf20c

OK Bill Nye.

I was kidding about the 87 octane. The joke was that shitty fuels = carbon buildup = higher compression. Let's not get all technical.

Hyper-X

IMO, it's not worth the risk of having detonation occur in the first place by using the lowest octane fuel. By recording the engine knocks via OBD2, you'd be able see the % of the occurance by using differing fuels and such.

RazorV3

we don't have 91 here, so i only use 93...or sometimes 94 from sunoco.

alexf20c

That's exactly it.


slalom44:
If the engine ran best with significantly retarded timing, the base parameter for closed loop would be significantly retarded. Yes, a functional knock sensor will sense the spark knock and pull timing, but that doesn't mean the engine is not being hurt. Even still, once the knock goes out of the knock sensor's range, and/or the ECU has accommodated the spark knock as much as possible (pulled as much timing as allowed), it will cut the spark and/or the injectors to individual cylinders. If you don't consider scored cylinder walls, burnt valves, fouled plugs, and seized rings to be harmful to your engine, then you'd be correct.

alexf20c

Look at it this way...

You're doing an alignment on your car, and the front camber spec is -4

CrazyPhuD

......91 for me.....the % premium get smaller as gas prices rise

pjkwong

I would say if don't plan on getting pass 5500 rpms on that tank you should be fine.