Octane rating.

[Petrus]

The R18 like most modern engines has knock sensoring and will change ignition timing accordingly.

I wonder how critical this is in the R18 engine. In other words how sensitive it is to the octane rating of the petrol.

Tomorrow going for a two up trip through the interior involving several mountain passes, I will fill up with premium 98 just out of curiosity. Do not expect to notice any difference but still curious and with the limited fuel capacity it does not break the bank.

Any of you have experience, knowledge concerning ths?

 

[emgarciax]

All other things being equal, higher octane will not lead to better performance.
So from interpreting BMW's recommendations my understanding is that 89+ octane will lead to best power output and the alternative fuel would yield lower output (by retarding the ignition) but safely.
My local Wawa gas station has unleaded E10 from 87 (regular), 89 (don't recall the name) and 98 (premium)
However, they also have Ethanol-free 89 and that is my choice.

 

[Gr8adv]

All other things being equal, higher octane will not lead to better performance.

Haha ok. That’s a crafty statement. All other things are the same paint color will not make a difference.

If the ignition timing is advanced to take advantage of the higher octane then there is a noticeable difference.

If you run lower octane than the bike is set to, the knock sensors will reduce the timing and and associated performance to match the octane.

If the timing is set to perform properly at 87, 92 will not improve performance.

Recommended octane with my Brentune is 92 or 93 if I recall.

 

[Petrus]

All other things being equal, higher octane will not lead to better performance.
My local Wawa gas station has unleaded E10 from 87 (regular), 89 (don't recall the name) and 98 (premium)
However, they also have Ethanol-free 89 and that is my choice.

The octane rating only affects performance if the knock sensor triggers the ECU to choose a map with less ignition advance.
As such the perfomance ís probably affected if a fuel with a lower octane rating than specced is used.

If a tuned mapping is used it can very well be that this give room for more ignition advance when a higher octane rated fuke is used. The ZZ1 in my MR3 can do with 93 but as I have changed the MAF hight the ECU advances the ignition at lower revs meaning it needs 98. The 98 vs 93 is not affecting the power; the ignition advance is.
Same thing my stage 1.5 modified VAG EA888. It can no problem run on 95 as it smply adjust ignition timing and turbo pressure but it pumps out the max on 98.

This illustrates that if the air intake (air filter) is changed and/or exhaust, a remap is used or whatever a higher octane rating may very well be effective. In other words; if modification give a better BMEP, then the specs have shfited.

Imo the question is more to the point for the R18 engine than for most. For one because the combution chambers are relative large and the revs low (so the burn front a lot faster than the piston making ignition timing more critical) and secondly because of the three different engine modes. ´Rock´ will without a doubt operate closer to the margins.
My question is about how critical/sensitve the R18 engine is exactly because not all thing are always equal. Altitude, humidity, temp. and even how you ride are basics affecting the engine´s fule rating ´need´. Anything which affects the RAD and thus BMEP affects the optimal ignition timing.

A caveat about US and EU octane ratings. There are basically three different test procedures with a different rating each for the same fuel. Over here in Europ the RON is displayed on pumps.
Most common is 95 E5 but 98 E5 and E10 is still widely available.

 

[Petrus]

Recommended octane with my Brentune is 92 or 93 if I recall.

RON?

Even though using too highly rated fule makes NO sense whatsoever, the BMEP is directly related to the effective compression ratio which is directly related to engine output. As such octane rating and ignition timing are a hot tuning thing.

Apart from the servo delete I have not modified inlet/exhaust but a do plan to faff with the intake. Just a few % more in will see an equivalent rise in BMEP etcetera.

Hence my curiosity.

p.s. anyone remember when in the previous century a car engine with a caburettor would pink when pulling a heavy trailer in a lowish gear whereas it would be ok in that same gear at the same speed without trailer?
The R18 electronics will adjust the ignition timing in an akin case like two up lugging up a hill.

 

[Petrus]

A side step to the ethanol as that doés change the power output; it has a lówer caloric value than petrol. More ethanol = less energy per liter.
E85 is nót a more powerful fuel. It does have a considerably higher octane rating and runs cooler because for max output it must run rich. If an engine is built for E85, i.e. with a considerably higher compression ration, than thát, the higher c.r. makes the engine produce more power.
Ergo do not confuse the power produced on E85 in an engine built to use that with the energetic value of ethanol. This is léss than that of petrol. I.e. an R18 engine will put out a bit more on E0 than on E5 than on E10 than on E15.

 

[beemerboy22]

The R18 like most modern engines has knock sensoring and will change ignition timing accordingly.

I wonder how critical this is in the R18 engine. In other words how sensitive it is to the octane rating of the petrol.

Tomorrow going for a two up trip through the interior involving several mountain passes, I will fill up with premium 98 just out of curiosity. Do not expect to notice any difference but still curious and with the limited fuel capacity it does not break the bank.

Any of you have experience, knowledge concerning ths?

I prefer to use the highest Octane rating available in my BMW R1250R if I am working the engine hard over the mountain passes e.g. switchback hairpins in Switzerland.

However I will not put (waste?) premium fuel in for a Sunday morning ride on flat roads or for a freeway trip.

 

[Noelpolar]

Mmm..... I strongly believe that higher octane fuel provides a benefit in my R18 at low revs and fullish throttle high load type riding..... so 1500rpm to 2500 rpm high load..... motor pulls cleaner on 98 versus 95.

Ai says....

Higher octane fuel provides greater resistance to premature, uncontrolled combustion (knock), which is especially beneficial in high-load, low-rev situations where engine compression and stress are high, allowing for more advanced spark timing and thus potentially better performance and efficiency for engines designed for premium fuel. For engines not designed for high octane, or without a knock sensor to adjust timing, using higher octane fuel offers no benefit and can actually lead to a loss of power or efficiency


Anyway... last ride without my bren tune was sad/awfull.... really noticed it..... new tune just dropped so off I go to load it.....

 

[Petrus]

see post #142 in ´my 10 cts´.

 

[bdalameda]

If you are riding at higher altitudes in the mountains higher octane fuels won't do anything as the lower air density reduces the engine compression.

 

[Petrus]

If you are riding at higher altitudes in the mountains higher octane fuels won't do anything as the lower air density reduces the engine compression.

Completely true. I also visit the coast though and it is the in between which is the crux.

Point being that 98 makes little to no sense for touring the stock bike over lóng distances.
It does make sense flogging it up slopes with improved breathing. Two up even more so.