Octane ratings and what they mean......

Ever facepalm at the completely inept that say "Run Premium in everything" but couldn't really find a write up to get your point across? I've been looking for something like this to explain why the bike saw a 5whp gain from just running 87 vs 93, and a guy with a '94 sho who thinks 93 octane is made from super special unicorn farts and pixie dust......

Well then, bookmark this.

http://www.brocksperformance.com/absolutefm/attachments/392/The%20Gas%20Factor%20by%20Don%20Smith%20from%20Throttle%20Nation.pdf

Enjoy, its a great writeup

If you focus purely on octane, that's true. But there's more to it than just that.

Stability is a big one in my experience. Low octane ethanol blended fuel in the gas can turns into some sort of non-combustable liquid quite a bit faster than high octane fuels do. Low octane fuels are quicker to gum up fuel systems.

It sound stupid, but ever since I quit running cheap fuels in my gas cans and therefore lawn mowers and weed wackers and dirt bikes and such, I've had far less trouble with gummed carburetors, hard starts, etc. Yep, I'm spending more money on that high octane fuel, like ~$5 a year more. I think I'm more than making that up in reduced repair times.

Not a problem or issue with my toys that get run regularly. Those machines have fresh(ish) fuel in the tanks at all times because of it. But for those that spend time sitting, I can honestly say I've found it worthwhile.

It's also very worth while to make sure those toys and the gas cans get stored out of the weather. Let no rain fall upon anything containing an ethanol blended fuel. Avoid condensation as well, if at all possible.

In reply to foxtrapper:

Actually even the "Ethanol safe" lawn tools extremely dislike any ethanol blend. This is why we use Countrymark's 90 plus NO ETHANOL. And yes is costs more than 93 octane blend.

If I found a supply of ethanol free fuel nearby, I would do it. I hear ghost stories about it being around, but when I investigate, it's not there.

Honestly, I'm not sure that's the end-all be-all of the story anyhow. I bought a Spitfire a few years ago that had been parked in the garage since the 1980's. When I popped the gas cap, the fumes just about bowled me over. I'd forgotten how strong gasoline used to smell and fume up. Almost wish I would have kept some of that fuel just for the novelty of opening up the can I stored it in.

Anyhow, I burned it because when I put power to that Spitfire it promptly started right up. After having sat for decades, it just ran. So I drove it and went with the modern fuels (which gave me separate problems with the ethanol dissolving various components).

Yep, where are you located and do you happen to have any countrymark/harvestland co-op's around.

there are a few stations in Portland ethanol free....

typically the ethanol free stuff sells for 10% ish more

yamaha wrote: Ever facepalm at the completely inept that say "Run Premium in everything" but couldn't really find a write up to get your point across? I've been looking for something like this to explain why the bike saw a 5whp gain from just running 87 vs 93, and a guy with a '94 sho who thinks 93 octane is made from super special unicorn farts and pixie dust...... Well then, bookmark this. http://www.brocksperformance.com/absolutefm/attachments/392/The%20Gas%20Factor%20by%20Don%20Smith%20from%20Throttle%20Nation.pdf Enjoy, its a great writeup

It's been a long time since I have seen a V6 SHO, but if the fuel door says premium fuel, you need to run premium fuel.

I couldn't begin to tell you how many times a car (that requires premium) will fail for NOx and the customer pinky-swears that they aren't running 87. Then when it comes down to "well, we have already checked/repaired everything else, you will need a catalyst" then they say "Well, I have been running 87, but it all comes out of the same nozzle so it's a ripoff." Nissan Maxima and 4.9 Caddy owners were the worst for this.

Always do A-B-A tests. You'd be surprised. I had one car get fuel economy better enough on 93 that it more than paid for the difference in price.

yamaha wrote: Ever facepalm at the completely inept that say "Run Premium in everything" but couldn't really find a write up to get your point across? I've been looking for something like this to explain why the bike saw a 5whp gain from just running 87 vs 93, and a guy with a '94 sho who thinks 93 octane is made from super special unicorn farts and pixie dust...... Well then, bookmark this. http://www.brocksperformance.com/absolutefm/attachments/392/The%20Gas%20Factor%20by%20Don%20Smith%20from%20Throttle%20Nation.pdf Enjoy, its a great writeup

I had a couple of minor issues with the article, but the only that really needs pointed out- what knock really is. The article said that it was just self combustion, which tries to back run the engine- and that is really bad.

That description is more like pre-ignition. And that's not good, but it's not knock. It does cause knock in many cases.

Knock is actually an explosion- in the technical sense. Where the flame front travels at the speed of sound, and has shock waves. It's those shock waves that bounce off of the wall that cause big problems. That's the sound of a hammer on metal you hear. It's what puts the small pits into surfaces, and hammers the rod to make the bearings contact each other.

Other than that, it was good. And most likely, the above explanation isn't that needed.

Knurled wrote: Always do A-B-A tests. You'd be surprised. I had one car get fuel economy better enough on 93 that it more than paid for the difference in price.

I have noticed this too. I wonder if some fancy computers now will advance timing until knock and then back off a bit to optimize for whatever gas you put in?

rcutclif wrote:

Knurled wrote: Always do A-B-A tests. You'd be surprised. I had one car get fuel economy better enough on 93 that it more than paid for the difference in price.

I have noticed this too. I wonder if some fancy computers now will advance timing until knock and then back off a bit to optimize for whatever gas you put in?

For the most part, yes. They will run the best that they can.

rcutclif wrote:

Knurled wrote: Always do A-B-A tests. You'd be surprised. I had one car get fuel economy better enough on 93 that it more than paid for the difference in price.

I have noticed this too. I wonder if some fancy computers now will advance timing until knock and then back off a bit to optimize for whatever gas you put in?

Yes, many newer cars have active anti-knock systems that will do just that.

oldeskewltoy wrote: there are a few stations in Portland ethanol free.... typically the ethanol free stuff sells for 10% ish more

locally I've got one station that sells 87 ethanol free … it costs more than 93 blended

rcutclif wrote:

Knurled wrote: Always do A-B-A tests. You'd be surprised. I had one car get fuel economy better enough on 93 that it more than paid for the difference in price.

I have noticed this too. I wonder if some fancy computers now will advance timing until knock and then back off a bit to optimize for whatever gas you put in?

That's a given in anything new enough to have a knock sensor, the real question is whether or not it hits the ceiling for max timing before it gets the car to start pinging on 92 octane. This is why you're unlikely to see much of a gain putting premium in your crapcan, its designed with timing parameters for 87 octane fuel.

In reply to Knurled:

It claims premium, but theres a signifigant number of us in non-emmissions states that have run the cheap E36 M3 for years(and most of us lack catalysts at this point due to Ford's retarded design of them)

The guy with the '94 sho I referenced in the first post most likely filled up with E85 like a dumbass. 87 octane will not cause a misfire/rich smelling/lack of power versus running 93.

Sky_Render wrote:

rcutclif wrote:

Knurled wrote: Always do A-B-A tests. You'd be surprised. I had one car get fuel economy better enough on 93 that it more than paid for the difference in price.

I have noticed this too. I wonder if some fancy computers now will advance timing until knock and then back off a bit to optimize for whatever gas you put in?

Yes, many newer cars have active anti-knock systems that will do just that.

Newer cars? A lot of OBD1 cars have at least a primitive version of the same feature. For example the stock ECU in a 4AGE will retard ignition a bit based on input from the knock sensor. You have to set the static ignition timing to a good-enough position yourself though.

honestly.. I started running premium in everything back in 1999 when I bought my Hyundai Tiburon. It was the first car I had owned with fuel injection. I found that with running 93 octane, I got mileage that was good enough to offset the price increase I was paying.. the added power was just a bonus at that point.

ever since then, all my cars have been "premium fuel only" so I have not had much of a choice

Ah me. All of this rhetoric ' As far as ethanol, as I have said many times I have a 19 yr. old snow blower and a 27 yr. old mower. Both are put away at the end of the season with a little stabil. Both always start right up and I have never had to replace any rubber parts. Both are fueled with 10% ethanol Sunoco fuel. As far as octane. Octane numbers are just a measure of anti knock ability. The higher octane numbers do not equate to any magical ingrediants. If your engine knocks on 87 then going up a notch in octane will improve things. Of course those that are convinced that 93 octane is the cure all, dream on and be happy with your choice. And people still add "dri-gas" in the winter.

that is just it.. most modern cars -will- knock at 87 octane.. the adaptive fuelinjection/ignition just retards the advance enough to keep it from happening. This cuts power.

The ultimate test though requires maths. In my Tiburon I did the math.. running on 87 and on 93.. and I actually got better mpgs on 93 than I did on 87

iceracer wrote: If your engine knocks on 87 then going up a notch in octane will improve things.

I don't agree with all of your post, but this is the absolute truth. Every automotive authority will tell you the same thing, and that trumps any one persons own experience. New cars are rated for a certain octane. That's what they need and nothing more.

the thing is though.. modern anti-knock systems are so good.. you never notice them in action. That is why I said you need to do the math. Do a couple tankfulls on 87 and a couple on 93 (or 92) and compare... if your MPGs go up, your car needs better octane gas

GameboyRMH wrote:

Sky_Render wrote:

rcutclif wrote:

Knurled wrote: Always do A-B-A tests. You'd be surprised. I had one car get fuel economy better enough on 93 that it more than paid for the difference in price.

I have noticed this too. I wonder if some fancy computers now will advance timing until knock and then back off a bit to optimize for whatever gas you put in?

Yes, many newer cars have active anti-knock systems that will do just that.

Newer cars? A lot of OBD1 cars have at least a primitive version of the same feature. For example the stock ECU in a 4AGE will retard ignition a bit based on input from the knock sensor. You have to set the static ignition timing to a good-enough position yourself though.

The car in question was a Digifant II equipped Golf. No OBD to speak of More or less it was L-Jetronic with ignition control tacked in to the same box. But still we are speaking of 80s tech, nothing fancy at all.

GM computers have "premium fuel" and "regular fuel" timing maps and if the fuel level sensor changes more than a certain percent between key off and key on, it will re-assume the premium fuel and run the timing up until it knocks to see where the fuel quality is at. They did end up having to bodge in some code they called "in flight refueling" to account for people who leave the engine running while filling up.

bravenrace wrote: New cars are rated for a certain octane. That's what they need and nothing more.

Not always.

My truck has two timing maps, and at least two knock sensors. It defaults to the more advanced map on startup, then goes back to the lesser settings upon seeing 3 knock events. It runs fine on 87, but there is a significant performance difference if I use 91.

EDIT: Knurled beat me to it.

mad_machine wrote: the thing is though.. modern anti-knock systems are so good.. you never notice them in action. That is why I said you need to do the math. Do a couple tankfulls on 87 and a couple on 93 (or 92) and compare... if your MPGs go up, your car needs better octane gas

I my neck of the woods premium is often $0.50 more per gallon. If a car gets 30 mpg with 87 it would need to get over 34 mpg with premium for premium to pay off. I'm guessing the improvements in mpg are often not that great.

Aforementioned Golf would go from 35ish to 40-42mpg. Buying 92 at $4.50-4.75 per gallon was painful but intellectually I knew that I was saving money.

Every now and then I torture myself by seeing how available rust repair panels are for that chassis. Which, of course, they are, and I'm not afraid of re-flooring a car anymore. Stupid stupid stupid stupid...

pappatho wrote:

mad_machine wrote: the thing is though.. modern anti-knock systems are so good.. you never notice them in action. That is why I said you need to do the math. Do a couple tankfulls on 87 and a couple on 93 (or 92) and compare... if your MPGs go up, your car needs better octane gas

I my neck of the woods premium is often $0.50 more per gallon. If a car gets 30 mpg with 87 it would need to get over 34 mpg with premium for premium to pay off. I'm guessing the improvements in mpg are often not that great.

that all depends on the car. Like the golf above.. it gets more than that 4mpg increase. you have to try it to find out.