Gas Octane (...should probably save this for February)

[DucDave]

Wirelessly posted (BlackBerry Giggity: BlackBerry8330/5.0.0.438 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/104)

My bike is mapped for 93. Doesn't matter if it needs it or not, it's my preference and I'll continue to use 93.

Uh...

....you'll never ......


(never mind...to easy!)

[BSR6]

It completely depends on the motor, and how hard you push it. Look at what the manufacturer recommends. They are recommending it for a reason. Sure you can put 87 in a motor they suggest 93 for, but why? Are you really saving that much money?

When running a lower grade than recommended fuel injection will compensate and eliminate the knock, along with other conditions that result, but wouldn't you rather put the right fuel in and let it run the way its supposed to? To me this is better than letting the computers change everything to less than optimal settings to compensate for cheap gas that you put in to save a couple bucks on your last fill up.

[DucDave]

It completely depends on the motor, and how hard you push it. Look at what the manufacturer recommends. They are recommending it for a reason. Sure you can put 87 in a motor they suggest 93 for, but why? Are you really saving that much money?

When running a lower grade than recommended fuel injection will compensate and eliminate the knock, along with other conditions that result, but wouldn't you rather put the right fuel in and let it run the way its supposed to? To me this is better than letting the computers change everything to less than optimal settings to compensate for cheap gas that you put in to save a couple bucks on your last fill up.

How often do you change your oil?

[e30addict]

How often do you change your oil?

Now THAT question is best left until February

[TheIglu]

I always wave when I can.

[Stromper]

As a percentage the 93 is a better deal than it used to be

Can you get benzene anywhere

[Yamarider]

"Premium" isn't better. It is not a treat for the motorcycle.

Octane rating is simply the fuel mix's resistance to knocking (preignition).

"Premium" doesn't burn faster or hotter. It actually is harder to ignite.

Nowadays, because ethanol raised the octane number, if the fuel has more ethanol, there are fewer BTU's per gallon. If you let the bike sit, and the ethanol evaporates, the octane may go down.

Use fuel promptly!

Research octane (RON) is higher with a given fuel mixture than motor octane (MON) so the U.S. mandates the octane number on the pump be the average of the two.

I use 87 because that is the recommendation of Yamaha.

[e30addict]

Octane rating is simply the fuel mix's resistance to knocking (preignition).

"Premium" doesn't burn faster or hotter. It actually is harder to ignite.

I've always heard something slightly different....

Higher octanes burn faster and cooler once ignited, but they ARE harder to ignite in the first place.

Not really sure if it's accurate since I've never been able to measure it in any way.

[Kurlon]

Under equal conditions they burn slower and cooler. You make them burn faster by upping the compression ratio, and the CR bump results in more power from increased volumetric efficiency.

[fjrrider RI]

interesting discussion: I run 87 in my rav and two bikes. When my gf fills the ninja she puts in 93 only since she had to run it in her last bike. I have never noticed any difference with the two fuels and do not get better milage on my FJR with the 93. All vehicles run without knocks on either. I don't believe any of them have a higher octane mfg requirement. Didn't know about the engine cpu accommidating different fuels now.

[obsolete]

Under equal conditions they burn slower and cooler. You make them burn faster by upping the compression ratio, and the CR bump results in more power from increased volumetric efficiency.

I was under the impression that a higher CR increases thermal efficiency. How is volumetric efficiency increased? Does it aid in the exhaust stroke in some way?

[Kurlon]

I was under the impression that a higher CR increases thermal efficiency. How is volumetric efficiency increased? Does it aid in the exhaust stroke in some way?

Better initial draw as the piston drops and the intake opens.

[neuthunder]

my WRX was averaging about 28-30 mpg running on 93 (manufacturers suggested octane) on my trip to upstate NY and then got stuck with some 91 on the way back and ended up with a MPG of around 20.

[brewmaster]

I had too laugh at the English folks over here who kept telling me American fuel is Shit. The reason being that it has a lower octane. I tried to explain to them but they refused to believe a Yank might know something as they think we are all stupid and fat.

[R1]

Jim will never use all that octane!

[butcher bergs]

Didn't know about the engine cpu accommidating different fuels now.

Other than mechanical FI, a large percentage of FI systems will naturally accomodate for many conditions including altitude in addition to fuel octane, so long as the proper sensors are equipped.

You will find that alot of the vehicles which have been custom tuned to some extent will suffer more than the OEM-tuned types simply because the fuel mapping (the algorithm in which the ECU uses to operate the engine) will be more or less limited to similar condition to which the vehicle was tuned.

That's why you see the full on tuner cars suffering during extreme temps and/ or altitudes....they simply don't have the software to adjust for that.

[Quigs]

93 in my R1, 87 in my BMW. Filling the bike, it's like a 90 cent difference once a week. Filling the car, it's a few bucks a few times a week.

[obsolete]

Better initial draw as the piston drops and the intake opens.

Hmmm I was always under theassumption that the main gains seen in highercr where from more effective and complete burn. Now I gotta read.

[butcher bergs]

Hmmm I was always under theassumption that the main gains seen in highercr where from more effective and complete burn. Now I gotta read.

Combustion chamber/ piston top design, valve placement and size....lotta other factors go into determining recommended octane besides spark and timing in NA applications

[DucDave]

my WRX was averaging about 28-30 mpg running on 93 (manufacturers suggested octane) on my trip to upstate NY and then got stuck with some 91 on the way back and ended up with a MPG of around 20.

WOW....that's a huge difference. Oh wait, it was all downhill going out...???

10 MPG difference between 91 and 93 octane? You sure there weren't other factors? Like, you picked up a trailer full of lead that you brought back?

[Stromper]

Wind

I thought back in the day there were additives etc. in the premium that wasn't in regular

Prob no longer true

There is the perfect time for ignition and flame propagation during a power stroke. You CAN have the the fire a little too soon without generating real knock. All newer cars have a knock sensor that retards the timing

[Kurlon]

Hmmm I was always under theassumption that the main gains seen in highercr where from more effective and complete burn. Now I gotta read.

Combination of things, but that was one of the factors I could get numbers for when tweaking my cheazy motor sim proggie I toy with on the side.

[rice_rocket]

I can say I have never noticed a difference in octane for bikes, but since it's such a small tank, I don't mind putting in the 93.. only because I'm used to it for my cars.

I've almost always driven turbo charged cars.. and this is when you need the higher octane. Knocking will not only hurt your car, but it hurts the performance big time. Of course, if you drive your car like a grandma every day, it probably won't make much a difference. When the wife drove my audi turbo for a long period, she used to always put in regular gas. The gas mileage was less even when she drove it. Once I decided to hammer it and it actually put the car into "limp mode" which the ECU sees enough knock it puts it down to an alternate fuel mapping. The car felt like it was running 1 or 2 cylinders less.

When I drive non-turbo charged cars.. ie the CR-V or Accord, the lowest grade will do perfectly fine. I did do a longer term logging and at MOST it was a 1mpg difference. So.. it didn't really matter.

I was told my latest bike ran rich from the factory, so I'm more than happy putting in lower octane gas, and I don't notice an issue. Also told that the 05 model does NOT have ECU remapping capabilities, ie it won't "learn" on it's own, so I'm waiting to see if it has any detrimental effects. Longer term tests are waiting until next season..

[ZX-12R]

Nowadays, because ethanol raised the octane number, if the fuel has more ethanol, there are fewer BTU's per gallon.

Octane only relates to a fuel's resistance to detonation. It has absolutely nothing to do with the BTU's, combustion speed, combustion temperature, or any other metric related to a fuel's performance. Ethanol has fewer BTUs than an equivalent volume of gasoline because it's (like other alcohols) partially oxygenated.

When running a lower grade than recommended fuel injection will compensate and eliminate the knock, along with other conditions that result

Most modern fuel injected cars have knock sensors which retard timing when knock is present but most injected motorcycles have a much simpler open loop system without knock sensing. They are starting to show up more in current models but are still far from common in bikes.

Look at what the manufacturer recommends. They are recommending it for a reason.

I always question what the manufacturer recommends (especially with performance bike engines) because of all the little tricks they do to conform to government rules while still trying to make huge peak power. Since proving one grade of fuel being superior to another is pretty difficult to do, have a look at the shifting speed recommendations in my 12R's manual. At 34mph, I should be changing to 6th gear. The bike is barely off idle at that speed in 6th gear and if you give it a lot of gas, the engine pings just like any other high compression/high RPM engine.

Shifting to second at 9mph is funny since it idles at 7mph in first gear!

[DucDave]

That is hysterical....34 mph in 6th gear! Is that even possible?