Confused by Octane - PeachParts Mercedes-Benz Forum

PanzerSD · #1 07-19-2011, 02:41 AM

K, so I've recently discovered the advantages of running premium and advancing my timing. With that said, I ad been buying my fuel at the Shell station, at a RON of 91 (as advertised) it contained 0% Ethanol.
Tonight I discovered that the Husky station around the corner has 94 on tap, but contains 10% ethanol. Higher octane, is higher resistance to knock.
From a performance aspect, 94 octane fuel should be great! but I read online that the energy contained in the fuel, ANY fuel, is reduced by volume.
is 94 @ 10% essentially diluted 91?

400Eric · #2 07-19-2011, 03:56 AM

No, but the 10% ethanol stuff will get slightly poorer fuel economy. Ethanol is good for octane but bad for fuel economy. (It's bad for power too unless the fuel is richened a bit when ethanol is added to the mix and your A/F ratios are not electronically controlled.)

The 94 octane fuel is beneficial to you only if the 91 fuel is pinging.
Regards, Eric

JayRash · #3 07-19-2011, 05:12 AM

ok the 450 usually runs slightly rich and i am more than sure that 10% eth will give u the right AFR just advance the timing a little so u really feel the power gain. how i wish they gave us such fuel mixes here. and 94 rating is due to the 10% ethanol in the fuel. try it and ull see u wont regret it.

OzC36 · #4 07-19-2011, 08:07 AM

Many references indicate that Ethanol may damage engines and fuel systems of Mercedes Benz cars manufactured prior to 1986. This use to be a direct quote from Mercedes Australia...but subsequent politically correct web site information on the subject now seems somewhat muted...

http://www.onlinemechanical.net/ethanol-E10.html

The octane rating of Ethanol is higher but the available energy (potential power) per unit of volume/weight of Ethanol is lower than the same amount of petrol.

JayRash · #5 07-19-2011, 09:54 AM

well i dunno, i used to spray ethanol into my engine all the time, but yes thats diffrent than running it thru the injection.

400Eric · #6 07-19-2011, 11:01 AM

Every poster in this thread so far has brought up some very valid points. I say if the OP has several cars he can fall back on if he hurts something, he can and should go ahead and follow Jay's advice and crank up the timing a bit to take advantage of the higher octane.
Regards, Eric

JayRash · #7 07-19-2011, 11:11 AM

im sure if he ups the timing he can get some really good midrange pull and atleast some 15 hp top end.

If my AMG didnt run on the lean edg of things from factory i would mix some ethanol in my tank. i already have the timing trick done but i hradly use it since i usually burn my HG using it, but the power increase is very very noticable.

400Eric · #8 07-19-2011, 11:26 AM

And that improved mid-range may also give back whatever fuel economy he may lose from the ethanol!
Regards, Eric

PanzerSD · #9 07-19-2011, 02:38 PM

Quote:

Originally Posted by 400Eric

And that improved mid-range may also give back whatever fuel economy he may lose from the ethanol!
Regards, Eric

I like this!

With 91 I run a bit off full advance, I'll put it to full advance (now that my timing light has returned to me) and see. the ETM Specifies 98RON for full advance.

JayRash · #10 07-19-2011, 02:39 PM

yes and 91 mon is = to 95 ron
thus 94 mon (E10)= 99 ron

PanzerSD · #11 07-19-2011, 08:22 PM

Fuel companies add Ethanol to their fuel to appeal to the "green" demographic, if it reduces the stored energy, and ultimately the efficiency of whatever engine it goes into, why is the industry striving for 85%+ Ethanol?? it defies common sense and logic to make a fuel, that's green, but you'll need more of it to do the same work as with regular fuel....just seems silly to me.

The numbers that are displayed on pumps. is that the RON or the MON? They don't specify, and nobody know locally.

bahaimus · #12 07-19-2011, 10:50 PM

Quote:

Originally Posted by PanzerSD

Fuel companies add Ethanol to their fuel to appeal to the "green" demographic, if it reduces the stored energy, and ultimately the efficiency of whatever engine it goes into, why is the industry striving for 85%+ Ethanol?? it defies common sense and logic to make a fuel, that's green, but you'll need more of it to do the same work as with regular fuel....just seems silly to me.

The numbers that are displayed on pumps. is that the RON or the MON? They don't specify, and nobody know locally.

Well, according to Wikipedia

Quote:

In most countries, including Australia and all of those in Europe, the "headline" octane rating shown on the pump is the RON, but in Canada, the United States and some other countries, like Brazil, the headline number is the average of the RON and the MON, called the Anti-Knock Index (AKI, and often written on pumps as (R+M)/2). It may also sometimes be called the Pump Octane Number (PON)

Now, from a performance perspective, and given this is the Performance Paddock, E85 fuel is a ****ing marvelous thing!

Sure you need more of it, but it's resistance to detonation allows a lot more power to be made for a given engine configuration (forced induction mostly) so long as your engine internals are strong enough to support that power.

It will be my fuel of choice for my track car where I am intending to run my M104 with stock internals and 10:1 compression ratio turbocharged. I'm thinking that so long as I can keep intake temps under control, up to 15psi might be alright.

So I am all for fuel companies making it more available!

bahaimus · #13 07-19-2011, 10:53 PM

Quote:

Originally Posted by JayRash

yes and 91 mon is = to 95 ron
thus 94 mon (E10)= 99 ron

Be careful here, there is no real equivalence between RON and MON unfortunately.

PanzerSD · #14 07-19-2011, 11:26 PM

Quote:

Originally Posted by bahaimus

Be careful here, there is no real equivalence between RON and MON unfortunately.

hence my confusion

So far, I do think that Husky's 94+10% goes a long way to smoothing my idle, allowing me to turn it down a bit, and move to full advance, but lacks the *bang* that Shell's V-power has. The flip side is that Shell's V-power, has kick, but even at 91, my idle suffers some, and my acceleration slugs when it's hot.

400Eric · #15 07-20-2011, 01:11 AM

Quote:

Originally Posted by PanzerSD

Fuel companies add Ethanol to their fuel to appeal to the "green" demographic, if it reduces the stored energy, and ultimately the efficiency of whatever engine it goes into, why is the industry striving for 85%+ Ethanol?? it defies common sense and logic to make a fuel, that's green, but you'll need more of it to do the same work as with regular fuel....just seems silly to me.

The numbers that are displayed on pumps. is that the RON or the MON? They don't specify, and nobody know locally.

If you want people to be forced into needing more of your product, it does make sense.

I can't address your second question because you live in the Great White North but down here they use a rating that is a cross between the research octane rating and the motor octane rating.
Regards, Eric