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Premium gas anyone?

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rockitcity

rockitcity

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Well on my usual weekly fill-up, my local Mobile station was out of standard and mid grade gas (I like the Fast Pass they offer as I don't have to use a debit card at the pump having been skimmed that way once before), so I decided to fill up with Premium. What the heck, it's only 3.5 gallons, so the price is negligible.

So, maybe it's my imagination or the weather, but it seems my 07 1250 runs smoother on Premium. Start-up idle this morning seemed to stabilize quicker and the bike just seems a bit "friskier" than on regular. Not enough so I would switch over on a regular basis, but subjectively feels better.

Anyone else try it and notice a difference? My bike's fairly stock with the exception of a Power Commander III and a Yoshimura exhaust that were on the bike when I got it. Maybe it had been tuned for higher octane?
 
I run Premium in my 05 FZ1, she also seems to start easier and ready to rev sooner, I do miss FI that my former 07 Bandit had but that's another story, the FZ compression ratio is 11.5, it runs fine on Regular but runs better on Premium, just the opposite on lower compression engines, from my experience they will run worse on higher octane gas.
 
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rockitcity said:
Well on my usual weekly fill-up, my local Mobile station was out of standard and mid grade gas (I like the Fast Pass they offer as I don't have to use a debit card at the pump having been skimmed that way once before), so I decided to fill up with Premium. What the heck, it's only 3.5 gallons, so the price is negligible.

So, maybe it's my imagination or the weather, but it seems my 07 1250 runs smoother on Premium. Start-up idle this morning seemed to stabilize quicker and the bike just seems a bit "friskier" than on regular. Not enough so I would switch over on a regular basis, but subjectively feels better.

Anyone else try it and notice a difference? My bike's fairly stock with the exception of a Power Commander III and a Yoshimura exhaust that were on the bike when I got it. Maybe it had been tuned for higher octane?
Click to expand...

PCIII may have something to do with it?
 
If the engine is of a higher compression, you can see gains in power. Most bikes won't see anything you will feel unless it is equipped with knock sensors/tuned for higher octane fuel. You also need a timing advance of a few degrees to get the extra pony or two that you could gain.
In lower compression engines, high octane is slower to burn, actually causing less power. You will get more of a gain by cleaning you're air filter in most cases than running premium.
 
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i need help with your statement that higher octane burns slower in an engine designed for low octane?
 
wanabeguru said:
i need help with your statement that higher octane burns slower in an engine designed for low octane?
Click to expand...
No problem
So octane rating number that tells us how difficult it is to ignite. Ethanol is 108 Ron, propane is 112, among your other flavors of petroleum. Ever wonder why people complain that e85 gives them less performance in most engines? It has a higher octane rating. The higher the number, the harder it is to make it go boom. Even if the engine can handle it from a corrosion standpoint, likelihood of it being optimized for it is next to none. Only turbos have this capability as they can adjust the input pressure prior to compression. This is why you see ethanol/methanol run in race engines. They have a high compression/boost level.

During compression, a fixed amount of gas (the physical state, not the fuel) is in a container (cylinder) that has its volume decrease, therefore pressure goes up, temperature goes up. We can thank the laws on thermodynamics for this. Fire pistons are another example of how this works.

Problem arises when flashpoints are taken into account. As you increase pressure, flashpoint goes down(assuming you keep temperature =). This is because the molecules are closer together. This is why msds will list a closed vs open cup flashpoint. Anyway, the closer you are to flashpoint prior to ignition, the faster it burns because of how pressurized the gas is. For instance, take black powder. Place it in an open pan, and its rate of combustion is lower. Place it in a confined space and it combusts quicker. This is because the initial phase of the combustion increases the pressure and heat causing the remainder to auto-ignite.

Back to fuel, if you're running a high octane in a low compression engine, you're further from the autoignition temperature at tdc. When your spark occurs, you burn a portion if the mixture to increase pressure for autoignition. But your cylinder is starting its power stroke, reducing volume, so it further takes longer for autoignition to occur, because the additional pressure has to build. If it never occurs, sometimes you will see it just flame out the exhaust and/or miss. To counter this, adjust your timing. Modern cars will usually have separate octane maps for ignition to help optimize this. Worst case, they just retard the timing if you put too low of an octane, but it is a short term solution.

Help any?
 
I run the cheapest gas possible. Only reason to run premium (aka Higher octane) is if the manual calls for it, or if you have done some modifications to increase the compression ratio.
 
rpcraft said:
I run the cheapest gas possible. Only reason to run premium (aka Higher octane) is if the manual calls for it, or if you have done some modifications to increase the compression ratio.
Click to expand...
Or irregardless of what your manual specifies if you're getting pinging/knocking best up the octane. That can harm an engine pretty quick.

_
 
Great subject.
When I had my '97 1200S there was another forum that had a couple of drag racing engine builders on it. This very subject turned into a debate and to prove their point they took a stock motored Bandit and dynoed it with various octane gas. The octane that produced the most power? 88. As they tested higher octane gas the H.P. was reduced. Once they started changing internal components, pistons, cams, head work, different head heights etc. that's when higher octane is necessary.
You may get additional additives with premium but otherwise it's a placebo effect. Another point is gas stations, especially rural ones, sell far less premium so you could potentially get stale gas to.
 
Everything I've read tells me that the best fuel to run in any motor is the one that it was designed for. If it is designed for premium, then it will run to it's best potential with premium. If it was designed for regular, then you will get the best performance with good ol' regular.
 
OK, I am going to break this down as simply as I possibly can. Octane rating is actually the controlled burn rate of the fuel. The higher the octane rating of the fuel the harder it is to ignite and burn completely. If you put higher octane in a motor that does not have high enough compression then it will produce less power because the fuel is not burning as completely as it could be. If you have knocking, then the fuel you are running is pre-igniting and you should increase the octane rating, or decrease your timing (if possible). It takes higher compression to make the fuel burn more completely. Higher compression is what is increasing the power of the motor combined with other improvements that involve air flow and fuel atomization (and spark timing, strength, and duration). That is why when you see race motors they usually have to run high octane race fuel, otherwise they would grenade the engine from detonation due to the lower burn rate of lower octane fuel. If you had the ability to run a constant wideband read on your o2 sensor you could actually see the bike running more richly when you run higher octane fuel (if it is sensitive enough). The reason the bike seems to run more stable is because it is actually running slightly richer, due to the larger amount of unburned fuel from reduced timing (on fuel injection it kind of happens right away). That is all theory but it gets supported when you can really get serious with a dyno and really accurate feedback loops.

When you go to a dyno to start tuning for peak power you ideally want to start off with a motor that has very little baseline advanced igntion (spark) and a nice fat fuel curve (rich). This ensures that you can get the motor to fire up, run cool, warm up to operating temp quickly, and break in ( if it is a fresh built motor) in a stable and as controlled manner as possible (meaning no backfiring or weird timing hickups that could cause detonation). Once it is broken in or baselined you start advancing the ignition until there are diminishing returns, and then you start leaning down the fuel curve to get a perfect AFR across the rpm spectrum. Once you get to that magic number you should be pretty darn close to making max power.
 
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Indeed, to put it even more simply. Octane has nothing to do with energy content, its only a measure of a fuels resistance to knock.
 
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