What about premium gas...

I'd like to chime in a bit. Knock (detonation) and pre-ignition definitely are very different, but they are also related. And detonation will certainly damage an engine, but its not like little pockets of fuel burning after the flame front has passed. Inside your cylinder you essentially have a little thermal cracker/reactor. The configuration of some gasoline molecules is such that they break down easier under the conditions in the combustion chamber to different hydrocarbons that are more prone to effectively exploding than burning smoothly like the flame front does as it passes through the combustion chamber. This occurs actually right up there at the flame front. This explosion not only creates a high pressure wave, but can strip off the boundry layer of cooler gas at the piston, cylinder wall and valves and allow for much greater heat transfer so that you wind up with pistons and other parts overheating and deforming. However, damage will not occur if the period of time that detonation takes place is short.

Pre-ignition gets you in a couple of different ways. One is that it effectively advances the timing significantly, which results in overheating among other things. The higher temperatures in the combustion chamber then lead to detonation as the gasoline that normally doesn't break down to explosive components does break down when exposed to higher temperatures for a longer time.

I've had to use regular instead of premium a couple of time and had no problems. But then, I avoided the conditions that zrider mentioned-high temperature (wasn't been too hard to avoid these this winter) and lugging the engine.

In a dire emergency, I'll use anything that will burn! Yes....I'll sacrifice my bike, even R² to help you, if duty calls. I've done it before. I'd do it again. That was my primary point. But, one need not panic if one can truly wait or pursue an alternate exit strategy. You know....measure twice and cut once.

HF

p.s. Lotsofwheels is technically very correct. I was merely trying to put it into simple laymans terms in a manner that helps everyone remember the primary difference between pre-ignition and detonation.....so they wouldn't worry so much. If we really explained it thoroughly, I guess we could fill up a couple of pages and folks would wonder what they just read. So, I tried to keep it simple. But I really like how Lotsofwheels explained it. That's better than how I said it.

We design (& hope) for a smooth flame front propagation thru the combustion chamber. For various reasons, parts of the fuel components, sometimes don't cooperate. They have mini explosions (so to speak) instead of smooth burns....for several different reasons affected by several varying factors. That's detonation (more or less). But its not nearly as complicated to resolve it: increase Octane rating.

Now, WHY that works so effectively.....I hand it back over to Lotsofwheels to explain. He's got a better handle on this than me. And I'm not being sarcastic. I'd love to read your explanation, if you know.

I'm not sure what HighFive is looking for since he said it all when he said that if you want to avoid knock(detonation), raise octane. Since octane is just a measure of resistance to knock, if you raise it then you're less likely to have knock. So if you modify your engine by raising compression ratio or advance timing you are changing the conditions in that tiny thermal reactor that we call a combustion chamber to conditions that are more prone to causing a gasoline molecule to break down, and thus you need more octane.

How is the octane of a fuel measured - in special engines for that purpose. Research Octane (RON) is measured in an engine where the compression ratio can be varied until knock is created. Motor Octane (MON) is measured in a similiar engine, but the intake charge is preheated and the compression ratio and timing are varied. Since the MON conditions are more severe and are more likely to cause a fuel to break down into the components that essentially explode rather than burning smoothly, MON is lower than RON for the same fuel.

The different ways of measuring octane is why there is sometimes some confusion in forums in discussing it. The average of RON and MON - (R+M)/2 - is posted on pumps in the US whereas in much of the world RON is what is given. Since MON is typically about 8-10 units lower than RON, the US posted pump octane winds up being 4-5 octane units lower than what would be shown for the same gasoline in say, Europe. So, sometimes apples and oranges wind up getting compared when talking octane.

The octane rating is actually based on comparing the resistance to knock to that of two different compounds that may be found in gasoline - normal Heptane = 0 and iso octane = 100. This just means that n heptane breaks down easily into components that detonate and iso octane doesn't do so as easily. What they actually break down to I don't know, but it's likely a whole soup of things. Whatever it is, the resistance to doing so - octane - is dependent on the configuration of the gasoline molecule, which affects the bond strength. Molecules that have carbon atoms aligned in a straight chain have lower octane than if the same number of carbons are in a branched configuration. Take the carbons and arrange them in a ring and the octane goes up. Knock off some hydrogen atoms so that you have double bonds between some of the carbons and the octane goes up. That's why something like Toluene has high octane - It has a benzene ring, which is six carbons in a ring with alternating double bonds between the carbons, and then has a methyl group attached to one carbon. So, it is the best of all worlds, a ring with a branch with alternating double bonds in the ring.

One thing octane is not is a measure of how fast a gasoline burns. It is a measure of how prone the gasoline is to breaking down into compounds that detonate. I suppose you could say that if you have knock you have extremely fast burning, but if there is no knock because you have sufficient octane, a higher octane gasoline doesn't necessarily burn faster than a lower octane gasoline. Also, at least with motorcycles with no knock sensor, you don't get anything by using a higher octane gasoline than what you need to prevent knock. Once knock is stopped by raising octane, you don't have to go any higher.

Blending gasoline in a refinery gets interesting because if you blend two components with different octanes the resulting octane of the finished blend is not the volumetic average of the octanes of the components, but something different. There's all sorts of correlations for doing gasoline octane blending, which range from something simple like having a constant for a gasoline component to add (or subtract) to its measure octane, to involved routines that take into account aromatic percent (benzene ring materials ), olefin percent (double bond materials) and even the octane of the mix. When you have numerous components that are blended into various grades of gasoline and you have to hit specifications not just for octane, but distillation, RVP, vapor/liquid ratio, driveability and a whole slew of reformulated gasoline requirements, and then have the specs vary from state to state, and sometimes city to city, and make sure you don't run out of the components or overflow the tanks because you aren't using them enough, and then try to come up with the most economic recipe, it can get complicated.

I've run on here and I doubt it provides anything useful. The best thing to remember is to have enough octane in your fuel to avoid knock, but more than enough doesn't get you anything. A little bit of knock every now and then isn't likely to damage your engine, but you don't want it to go on for long.

Superbly stated....LotsofWheels! Reminds me of those long staff meetings in my refinery days.

And you summed it up well, by restating the most important point about Octane....which is all anyone really needs to remember: Higher Octane won't make your bike run faster. It just helps eliminate Detonation, if you are experiencing that. If 91 Octane does the job, you won't gain any significant benefit (like more HP) by running 93, 96, 101, etc. Don't worry about some periodic Detonation over the short haul (a few hundred miles). Just change to higher Octane at next convenient opportunity. It will hurt your engine over the long haul, if you ignore it.....i.e. thousands of miles of frequent Detonation.

If your engine is NOT Detonating on 87 or 89 octane gasoline, then its just fine. Run it forever on that stuff, and save some $$. Unless, for some unjustified reason, it makes you lose sleep at night. In that case, run 110 octane. A good night of sleep may be worth every penny!

Case Closed.

HF

What an outstanding explanation of octane and fuel mixtures and what it means to us mere mortals! Thanks so much -- I feel more confident in baffling the bar guys on trivia night now!

I can vouch for the difference in performance when using regular over premium... Shewolf can back me up on this one... How much better was my bike running after we swapped the fuel out for some 94 octane?

Crap...your bike ran like a half dead lawnmower on whatever shit you had in there. Works awesome as drip torch fuel.

SheWolf wrote:

Crap...your bike ran like a half dead lawnmower on whatever shit you had in there. Works awesome as drip torch fuel.

Just call me and Torch the drip torch fuel delivery system

ZED wrote:

Around town here premium is pretty common. In the backwoods places it can be tough. If I go touring on the WRX I'll likely carry a small bottle of octane boost like I do on my Ducati or Z1000. Pre-ignition is bad and that's what can happen from low octane fuel in an engine which specifies a minimum octane rating.

perfectly said. cant find fuel in a high enough octane? bring a BOOST!!!!!! ya know,,,,like in the video games??? seriously though...i wouldn't go anywhere without an octane booster. it never hurts. and if it does at least youll be on you motorcycle.

pemex crude is often refined in the us and sent back for MX doemstic consumption.
http://www.wharton.universia.net/index.cfm?fa=viewArticle&id=1711&language=english

oldirt wrote:

I am not sure about the "leaded/unleaded" race gas. a friend at a dealer that sells race gas claims that they blend the race gas with pump gas. I have read that this is not a good thing, I am not sure of the ratio they are blending at, but I think the only reason they blend is to reduce the cyclinder and head temp in their dirt bikes.

BTW, last year at the Baja 500, we were putting "Pemex" premium through a 500+ HP fuel injected Trophy Truck Pre-runner. ODDLY enough the truck ran good for the 4 days of pre-running and chasing the BAD BOY race truck. I may not have done that, but it was not my truck. BUT it worked !!

bocaj wrote:

another plus to premium is no ethanol. At least at my nearest station it isn't. i also look for stations with separate pumps for premium.

fuel grade & ethanol are not related. when a driver pulls up to a refinery he has 30 or so choices/variables in what goes in the tank. he can get branded (say conoco which is just the base gas stock with certain predetermined things added) or unbranded (everyone all gets the same refined base gas. independant drivers/gas stations can buy/use any gas they want to pay for. company truck driver put their brand in their trucks, but the refibnery will sell them anything), different grades, different additive packages, ethanol or not added. gas stations receive tax credits from selling gas with ethanol added. it makes their gas cheaper & thus they make more $ per gallon. a few gas station owners will not sell ethanol gas as they know it's negative affects, even if they price match and loose some $ compared the competing shop accross the street. i support these gas stations & owners.

sorry to resurrect an old thread but:

If my choices are 90 octane which contains 10% ethanol (has to be marked as such by law) or 87 octane which doesnt - which is better to put in?
Alot of the rural petrol stations over here only sell these two choices.

Octane wise they are probably pretty equal since ethanol will give false boosted octane numbers (from what I have read). I would try the the non-ethanol (assuming it's cheaper) & see. Besides non-ethanol stores longer & you can always try an octane booster as well. In a perfect world -- super non-ethanol.

If it was me......I'd go lower octane. That ethanol sucks ass.

After hitting some small town country stores and seeing bags on the pumps except the 87 grade I decided to get and carry with me a bottle of octane booster. The Mom and Pops stores have some nice people to talk to a few minutes but the fuel is not always good-or free of water.
Since the Georgia mountains have a lot of motorcycle traffic the stores carry decent fuel but a bit farther south of where I live in Athens are small farm towns and the fuel issue is not so good. Generally 87 grade, diesel and kerosene only. Now if I had a Hayes M1030M1 or MD670F I could run diesel or kero with no problem.

HmmMmmm Well, here is my experience on the premium only vehicles.

I have an Acura RSX-X that requires premium only. When it was new and somewhere around 4K miles, I was running on fumes and the station I went to only had regular, so I pumped in about 5 gallons until I could find some premium. The car ran exactly the same, with no knocking or pinging under load ... so as an experiment, I filled up with regular and ran the whole tank out. Still no knocking or pinging. I couldn't even detect any drop in gas mileage. The car has 120K miles on it now and runs great ... so much for premium only. Oh, I forgot to say, at one point along the way, I went back to premium to see again if I could tell any difference, but I couldn't.... so regular it is!.

I also have an 02 Yamaha R6. I've run regular in it since day one and it runs like a scalded cat! Never a ping or knock. I'm betting if I raced, it could benefit from premium, but I just ride on the street and it's happy as a clam on regular. It now has 10K miles.

I just got the WRR and it probably came with premium in it .... I'm going to try a tank of regular just to see if it knocks or not. Most of my riding is easy street riding, so I'm not too concerned.

The only things I own that get pissed off with running regular is an old H2 Kawasaki and a 98 CR250. Those bikes will knock on regular and I gotta keep em happy with 93 octane.