87 octane in a M60 eat? mark?

[tim]

Yeah I know. Don't run with scissors, pet wild animals, etc.
But the physics of it suggest that you would get more power- at the risk of detonation-and a savings of $7/tank.
But for the favored few who own the big block 8, wouldn't vanos compensate for the higher/faster burn of the lower octane fuel? And still preserve the performance/mileage gains from the chip? On the pre-vanos 6's I can clearly see why you couldn't/shouldn't.

My m62 goes like a scalded dog on 87. apples and oranges yes, but I'm just curious. Is it safe to experiment? Seems like a backdoor way to further tune the fuel mapping, by altering octane in a chipped car.

I don't want to be the first, but I'm pretty sure it's not going seize up just trying it. I know what pinging sounds like but I've never once heard it in any alusil m60 or m62.

[DaCan23]

I would think that using 87 in a M60 would actually cost you more as your power and mpg would drop significantly... and at the possible cost of trashing your injectors or engine.

You can try to run 87, but would go for a MobilExxon or Shell or etc... that uses good additives, but non additive 87 would ping like crazy.

With most "chips", especially in a V8, I think they recommend 91 octane, so I'd be pretty scared using 87.

[DaCan23]

I think that it is highly unlikely that your car (or any car for that matter) will get better mileage with a grade of fuel that is higher than what the manufacturer calls for in the manual. Why? Simple, if an engine is designed to operate at peak efficiency, said efficiency will degrade to a certain degree as you move away from the recommended fuel grade.

The whole thing is that the different grades of fuel take different lengths of time between the spark event and when the flame front is fully organized. The lower the grade of fuel, the quicker the flame front is developed. Engines are designed with certain combustion chamber configurations and compression ratios so that when fed the proper grade of fuel, the Peak Pressure Point (PPP), which should theoretically happen at about 15 degrees after TDC. If you use a lower grade of fuel than what is called for, your PPP occurs sooner at say 10 degrees after TDC, and that is where "Pinging" or "Detonation" (sorry Shifty, "Pre-Ignition" is where the fuel combusts on its own before the spark event, hence the name "Pre-Ignition", this condition WILL destroy and engine very quickly) occurs. Detonation is in essence the flash combustion (instead of the flame front smoothly burning all of the fuel in the combustion chamber) of some amount of end gas due to the higher pressures associated with the early PPP. The issue here is the degree of detonation, a very little is considered harmless by some and beneficial by others, personally, I'll refrain from comment. Moderate detonation, where you can hear light "Pinging", is where the problems can start. A brief Pinging event when you first press the throttle is most likely harmless, however, if said Pinging continues, engine damage (in the form of burned valves, burned pistons and broken rings) can result. Severe detonation, a condition which is extremely rare in modern engines, can destroy an engine in a matter of moments.

The flip side of using too low of a grade of fuel is using too high of a grade of fuel. Now the flame front takes too long to get fully organized, resulting a late PPP of say 18-20 degrees. Now what happens is that your fuel is far from being fully burned before the exhaust valve opens, and as such, the flame front continues burning fuel right past the valve and into the exhaust manifold. Basically harmless, but since it doesn't convert the resultant heat into mechanical energy, it is also highly inefficient.

Now let us add modern electronics into the equation. My BMW, which carries a "Premium" fuel recommendation from the manufacturer, can run safely on lower grade fuels, however, the computer senses that detonation is occurring and retards the spark event. The delayed spark keeps the PPP at that engines' designed in optimum point. Unfortunately, since the ignition has been retarded (resulting in cooler temperatures in the chamber), the engine is not running at peak thermal efficiency, hence lower mileage and power.

Regarding cars that carry a "Regular" fuel recommendation, it is unlikely that the engine in said cars was really designed for "Premium" fuel, and as such, said engines will not benefit from higher grades of fuel. Using higher grades of fuel in such a car will most likely result in LOWER mileage per gallon of fuel, and possibly INCREASE combustion chamber deposits, which is never a good thing.

Rule of thumb. Use the fuel that your manufacturer recommends.

[632 Regal]

I think the whole issue with premium in these engines was to avoid higher sulpher fuels such as in lower octane fuel.

Sulpher is what causes the infamous Nikasil falure syndrome...also contributes to burned up cats.

The engine requires mid grade 89 octane factory, 10.5:1 complession on the 3 litre and 10:1 on the 4 litre engines is why they need the higher octane.

Dont forget that lower octane burns cooler and slower so the only way to make it work is retarding the timing which would make the engine more inefficient using even more fuel.

It is possible to use lower octane with a well designed water injection system.

[uscharalph]

I thouhgt you had to run at least 91 octane with an eat chip because of the anti-knock sensors. I don't have a chip yet, but that is what I remember reading.

[JonE]

Hi Ralph,
I think our M30 and M20 engines did not come with knock sensors, thus, making it even more important to pick the correct octane. Since ours don't automatically adjust timing, our margin of "error" with octane theoretically will be smaller. Personally, I have the EAT chip in my 535i and it seems to run fine on anything between 90-92 octane. I haven't noticed any pinging. On the other hand, I will NOT risk it with 87 octane!
JonE