regular vs. premium gasoline?

[StageLeft]

I mentioned above, and I think it was car and driver, that they had three vehicles all that asked for 87. They put in higher octane gas. One of the vehicles' computers actually eaked out a couple of extra horsepower (nothing you'll notice). Rmemeber this engine called for 87, so putting in 91 was basically a total waste of time, except for that couple of HP. One of the vehicles they threw a higher octane into actually _lost_ about 1.5% of its power. They attributed this to bad testing on their part, since their experts couldn't understand how a higher octane would reduce power (according to them).

Of course as most people here have mentioned, if your manual calls for 87 and you're putting in anything higher you are simply throwing money in the toilet, and it's that simple.

JBT's girlfriend's civic which knocks unless running on 93 has something wrong with it - I've actually noticed the same in my sentra. I should probably run something through it, but some older cars do knock without the higher octane, but its only because the car's engine is not in an optimal state.

 

[0roo0roo]

yea i saw that article too

 

[Vortex22]

My mom's Highlander knocks on anything lower than 91 octane... pos

 

[GalvanizedYankee]

At 8000rpm the combustion event is happening 66.6 times a second. The devil you say

A good racing engine with fantastic combustion chamber design will produce very good power

with as little as 24 degrees BTDC of ignition advance. To produce a good burn it should be compleat

at 3 degrees ATDC. These motors are the exception. Most street motors run in the mid-30's at full

throttle at torque peak and that peak could be at 2800rpm.

 

[Jeff7181]

You guys can argue about it all you want... I've seen the results first hand on engine dyno's more than just a few times.

And by the way, Pacfanweb, making a statement as bold as "WRONG" sets you up for a big plate of crow... if you want to be taken seriously, provide proof of your claims.

 

[Jeff7181]

Originally posted by: Eli

Originally posted by: 0roo0roo

So basically you're saying you can use whatever gasoline you want because the ECU will completely remap the spark curve, from idle to redline, getting the most power you possibly can out of the engines design and the fuel it's using?

i dunno, but based on what has been said so far, why not? it'll damage the engine, but it'll work

Well, it shouldn't hurt anything as long as the system is indeed keeping it from knocking, but I just had no idea that the spark advance on an A-B econobox would do something like that.. at least to that extent.

I am still a little confused though, and I think maybe the Japanese makers do it differently, due to the quote from that Toyota PDF...

Did you miss the quote from Chapter 16 of that book?

 

[Jeff7181]

Also, since I don't think you read the whole article I linked to... here's some more pertinant information...

Knock Detection Control

The KNKN (knock) input signal is critical in the prevention of engine detonation. The ECM uses the knock sensor(s) to determine whe, and to what degree, engine detonation is occurring and t hen retards ignition timing as needed. The spark advance program is designed to provide the maximum spark advance possible, while keeping the engine from producing an audible "ping". If problems occur with this input signal, detonation may result, producing significant levels of HC and NOx emissions.

... There are many varialbes the system must consider when determining the proper spark lead time. Coolant temperature, fuel quality, and engine load are just a few of the many factors that can significantly impact ideal ignition time. The ECM determines proper spark timing by applying various input signals against a proprogrammed spark advance strategy or "map".

So you see, it does use the map that's programmed into the computer. If you know what a ESA map looks like, you know there's no scale on it for octane rating. It doesn't care what octane rating the fuel is... it simply looks at all it's inputs and advances timing until the input from the knock sensor tells the computer it's detonating. Of course, if you put diesel fuel in you'll never get detonation, in fact, you might not even get combustion, lol... but my point is, of course the engine isn't going to set the spark advance at 180 degrees... but using a higher octane gas will raise the point at which detonation occurrs and the computer doesn't have to be programmed for 92 octane fuel. That's the whole idea behind computer controls... the map is a guide for the computer to follow... if under a certain operating condition, the computer finds the guide to be inefficient, it can change it... not perminantly, but after running 92 octane for a while, it might decide that through the whole operating range of the engine, it operates more efficiently with 2 more degrees of advance than the map calls for. So it learns that, and uses that to determine spark advance. Disconnecting the battery will erase all that information that it's learned. That's why when you disconnect a battery to replace it or something, the car might run different than before because it lost all it's information that it has gathered to learn how to operate the engine at peak efficiency.

*EDIT Whether 92 octane is worth the price difference is debatable.

Lets say you get 28 mpg on 87 octane, and 87 octane costs $1.70 per gallon, and your tank holds 15 gallons. That means you can drive 420 miles on $25.50 worth of gas. You end up getting 16.47 miles per dollar of fuel.

Now lets say you get 32 mpg on 92 octane, and 92 octane costs $2.00 per gallon, your tank still holds 15 gallons. That means you can drive 480 miles on $30 worth of gas. You end up getting 16 miles per dollar of fuel.

So 87 octane is still your best bet in this case... which by the way is a real example. On my way down to Florida in a 2001 Sable with Ford's 3.0L DOHC 24 valve V6 I ran 87 octane and got 28 mpg on the expressway. Once I got there I started putting premium fuel in it, 92 octane. And after a week of running it on that, when I drove back I kept using 92 octane and got 32 mpg. Wasn't worth it based on my calculations... but it was interesting to see a 4 mpg increase just by switching the grade of fuel.

 

[Slickone]

Originally posted by: Zenmervolt

Originally posted by: Slickone

Originally posted by: Zenmervolt

Originally posted by: Slickone
No advantage, not cleaner, not smoother, not faster (unless your engine needs/can use it). As mentioned, go by your owners manual. It's actually less clean, since it has additives to make it burn slower. Using higher octane when you don't need it can actually do more harm than good by leaving deposits since if your engine doesn't need/can't use it, it isn't fully burned.

Wrong. Using higher octane than required will do not harm to your engine. It will harm your wallet, but not your engine. The only thing that octane does is raise the self-ignition point. A spark plug in any engine operating with a stoichiometric fuel/air mixture (i.e. any modern engine) will ignite the fuel/air mixture for a full burn regardless of the octane level of the fuel and regardless of the engine's octane requirements. Octane prevents self-ignition from compression before the spark plug fires, which is a concern in high-compression engines.

Whoever gave you that "information" about higher octane fuel being less clean should not be allowed to touch a car.

ZV

Funny, that's the first time I've heard anyone disagree. I've read all over the place and seen it explained that way quite a bit. I've hung out on auto forums for years too. But I don't have time right now to even argue, much less get refs, etc. BTW, I didn't say it'd 'harm your engine' per se.

Explain to me how "Using higher octane when you don't need it can actually do more harm than good by leaving deposits" is not saying that it will harm your engine. I'd love to see how you get out of that.

Ahem. Because one is saying "Using higher octane when you don't need it can actually do more harm than good by leaving deposits" and one is saying "it will harm your engine".
I didn't say "it will harm your engine". I didn't say "engine". "Can do more harm" could mean that it's *possible* it could lower your horsepower, as Eli mentioned. Also I said "more harm than good", meaning it will do absolutely no good, so even the slightest negative that comes from using a higher octane is more than the good it will do. Also I said "it can", not "it will". There you go.
So what do you think gives higher octane it's higher ignition point? Does it not have more BTX complexes?

And I hate to tell you this, but I've hung out on automotive forums for years as well. They are some of the worst places to get automotive advice unless you know what you're talking about before you go there. The typical automotive forum has perhaps 5 members who know what they're doing and the rest just spread BS theories. Incomplete burn always indicates a fault in the engine, generally fuel delivery (too rich, non-stoichiometric fuel ratio, often from poorly done modifications to the ECU) or spark (dirty/old plugs, weak coil or worn out plug wires). You can run premium fuel in a lawn-mower and it won't leave deposits. I say again, your "information" is bullsh!t unless you're trying to use jet fuel or something.
ZV

I didn't say forums are where I got all my info. I know there are many clueless people in forums. Many in this thread (not referring to you).
BTW, calling someone's information bullsh!t is pretty immature. How old are you?
BTW, what happens when you use jet fuel in a piston engine? What happens when you use gasoline in a gas turbine engine?


This isn't an article I've seen before and isn't 'the article' that made my mind up. I don't know who this is. Anyway it says:

As to usability in a motor, ultra-high numbers are questionable. Octane will make up for some sins that an engine builder might have built into the motor, but an engine only needs what it needs... not a bit more.

Also:

TOO MUCH OCTANE CAN BE BAD!
Right now in the racing fuel business, there's a race to market the highest octane fuel that you can make. People relate the highest octane to "my motor is making more power." That couldn't be further from the truth.
One of the downsides to building a fuel with ultra-high octane is adding components that really slow down the flame front in the combustion process. You can get the flame front so slow, that the engine is now running in a too-rich condition. This takes away horsepower. So here you are, slowing down the flame front and getting rid of detonation, at the expense of losing horsepower.

BTW, that's "harm".

The bottom line is this: let's say your motor needs 92 octane to run correctly and you fill up with 125 octane wonder gas. You will not run any faster. In fact, you might end up running slower because of a radically slowed flame front.

BTW, I know this doesn't prove the 'ECM not adjusting to higher than stock settings' issue.

Originally posted by: 0roo0roo
your engine in newer cars can compensate for wrong octane with changed spark timing, but it cannot use it to advantage. only the oil company gains.

It will compensate for lower octane than it needs by reducing the timing, but how is it going to 'compensate' for higher than it needs? AFAIK most ECM's won't advance the timing beyond factory spec, unless you have aftermarket programming will they? Though I hear the 350Z will take advantage of higher than 93 (so people use 100+ race fuel), but perhaps thats because even 93 isn't really high enough for it's compression and it's always retarding at 93 or lower. If all cars could do this, all the honda boys would be running race fuel 24/7.
Edit: Thread was so long, I was typing this as I read, before I saw Eli's post, which is similar to what I'm saying.
Also as I was reading the quote from the GM book, I was thinking the same thing as Eli; if Jeff7181's point was true, octane ratings are meaningless. I don't think car manufacturers decide what horsepower a car will have by the octane rating. "Well lets tell them to use this octane so it will have this horsepower". They want the highest they can get. Horsepower sells. They'd all be saying to use 93.
AND if his point was true, there would be much less need for aftermarket ECM programming.


Scoorb, that car that gained HP could have raised it's compression over stock due to carbon build up, thus needing higher octane.

 

[Kelemvor]

However doesn't using Higher Octane gas burn cleaner and therfore it's better for the environment regardless of whether your car needs it or not? If this is NOT true, anyone have an official link stating such? We had this discussion yesterday about saving money vs saving the environment...

EDIT: Apparently I need to educate the guy who was arguing yesterday. he said he uses the higher octane (premium) gas because it's better for the environment. Apparently that's completely backwards....

here's two pages I just found...

http://www.cheap-auto-car-insurance-quotes.com/Potpourri/environment.htm
(excerpt below)
WATCH YOUR OCTANE USE. Most likely, your car doesn?t need premium gas. Modern engines don?t benefit from it in any way. And, octane creates more pollution. So unless your car manual specifically recommends the use of premium gasoline, DON?T USE IT. Regular gas is less expensive and less harmful to the atmosphere.

http://www.betterworldclub.com/environment/travel_tips.htm
(excerpt below)
On the road, fill up with the lowest octane gasoline possible. The higher the octane, the more hazardous pollutants released when fuel is burned. Only 1 out of 10 vehicles manufactured after 1982 require high-octane gas.

 

[Pacfanweb]

Originally posted by: Jeff7181
You guys can argue about it all you want... I've seen the results first hand on engine dyno's more than just a few times.

And by the way, Pacfanweb, making a statement as bold as "WRONG" sets you up for a big plate of crow... if you want to be taken seriously, provide proof of your claims.

I'm not the one who needs to provide proof. I'd say 20+ years working in service, numerous ASE and Ford certs. tech school auto degree, and specializing in driveability gives me a at least the benefit of having what I say taken seriously unless proved otherwise, which you have not done.
Your PDF says NOTHING about an ECM(or PCM) having an infinite limit for max advance....it only says that it can adjust the spark curve to prevent detonation. Nothing in there would lead me to believe that the ECM would jack the timing to 40 degrees, say, to take advantage if you poured some 100 octane unleaded in the tank....and I'm willing to bet a dime to a dougnut that it wouldn't.
There is a limit of how far an ECM can adjust timing. Period.

BTW, your quote, responding to Eli:

Putting premium fuel in WILL change the maximum spark advance the computer will use... that's a fact

This means nothing...it just says that the ECM will go to its maximum preset timing if high enough octane is used. You were responding to Eli's comment that there are set limits, which there are.
Not all cars are as variable as the one you described, and that is what I was originally responding to.
You say you've seen the results on a dyno....fine, big deal. What kind of car was it.....a hot rod of some sort, or a daily grocery getter like a Taurus or a Cavalier?
If you are claiming that an ECM has no limits to its ability to adjust timing, why are there engine tuners all over the country, and chip manufacturers that sell things that increase the max timing?
Maybe because there's a limit in a stock ECM? Exactly why.
Now, you are correct in saying that all ECM's can adjust timing to reduce spark knock, but not all have built-in ability to adjust for either 87 or 93. Most cars have a max advance that the ECM can do, and that's regardless of what octane gas you put in it.
I said that UNLESS A VEHICLE IS DESIGNED TO USE PREMIUM, you're pissing money away....and if the ECM has the afore-mentioned adjustability, then it obviously is designed to used premium and what most here are saying about using regular doesn't apply. And sure, if you change from regular to premium on one of these cars, you will see a difference on a dyno. Not much, but there will be a difference.
However, the vast majority of cars do not have this feature.

 

[Pacfanweb]

Also as I was reading the quote from the GM book, I was thinking the same thing as Eli; if Jeff7181's point was true, octane ratings are meaningless. I don't think car manufacturers decide a car will have by the octane rating. "Well lets tell them to use this octane so it will have this horsepower". They want the highest they can get. Horsepower sells. They'd all be saying to use 93.
AND if his point was true, there would be much less need for aftermarket ECM programming.

You are right, IF his point was true, which it is not. There are limits to all ECM's in max advance. Actually, neither his link nor his quote say otherwise.
I think that what we may have here is simply a misunderstanding, or a misinterpretation of a manual. If we were all sitting around having a drink and doing a bit of bench racing, this subject would last about 5 minutes until everyone was on the same page.

 

[Vic]

Just to summarize and close out this thread:

Read your vehicle's owners manual and follow it. It's kinda just like motor oil. Follow the simple instructions contained in the owners manual. You do not know more about your vehicle, how it operates and what is required to maintain it, than the engineers who designed and built it.

In general, only vehicles with high-compression or forced induction engines require high octane fuel. There are some exceptions though, like engines that have been modified with aftermarket parts and tuned to within a inch of their lives, or older high mileage engines that are "pinging" under load or in warm climate conditions.

The vast majority of vehicles do not require high octane fuel and (most importantly) will not benefit from it in anyway. In other words, if you own a Camry, a Civic (non VTEC), or Sentra, save your money, don't waste it on premium, and buy regular.

 

[RobCur]

funny, how no one seem to know why their are 3 grades? yet you ali,say its different octane level well duh! which is 3 different quality(same thing, worded differently!). all car manual says unleaded fuel, not plus or premium. Its a matter of choice and preferences..
Why use lowest octane on a weak car??? it does not make sense to pay less for a very fuel efficent car like volkswagon etc or any small engine.
this arguement is getting pointless.es.s.s buy whatever you want and say whatever you like.. end of discusssiosns.s

 

[duke]

Originally posted by: RobCur
funny, how no one seem to know why their are 3 grades? yet you ali,say its different octane level well duh! which is 3 different quality(same thing, worded differently!). all car manual says unleaded fuel, not plus or premium. Its a matter of choice and preferences..
Why use lowest octane on a weak car??? it does not make sense to pay less for a very fuel efficent car like volkswagon etc or any small engine.
this arguement is getting pointless.es.s.s buy whatever you want and say whatever you like.. end of discusssiosns.s

You, Sir, are an Idiot.

 

[Eli]

Originally posted by: RobCur
funny, how no one seem to know why their are 3 grades? yet you ali,say its different octane level well duh! which is 3 different quality(same thing, worded differently!). all car manual says unleaded fuel, not plus or premium. Its a matter of choice and preferences..
Why use lowest octane on a weak car??? it does not make sense to pay less for a very fuel efficent car like volkswagon etc or any small engine.
this arguement is getting pointless.es.s.s buy whatever you want and say whatever you like.. end of discusssiosns.s

You are ABSOLUTELY, without a doubt, one hundred percent incorrect, and you have absolutely no idea what you are talking about.

What are you talking about, nobody seems to know why there are 3 grades? There are 3 grades because different engines require different octane levels.. Hello, McFly? Read the thread. Over, and over, and over.

All car manuals DO NOT say Regular Unleaded. DO NOT. You go find me a 2004 Maxima manual that says the car takes Regular. You will not be able to, because the 2004 Maxima requires PREMIUM.

PLEASE educate yourself before you spread your bullsh!t to people that don't have a clue.

It is NOT a matter of choice and preference, it is a matter of NECESSITY. If you run Regular unleaded in an engine designed for Premium, you could DAMAGE YOUR ENGINE. If you run Premium in a car that was designed for Regular, you are wasting your money. It has NOTHING to do with the quality of the fuel. "Octane" is not another word for quality.

It is not a hard concept to understand. Under heat and pressure, gasoline vapors will spontaneously ignite. The octane rating is a measure of how easily the gasoline vapors will ignite under pressure.

Dear Lord, with your reasoning, I should have to put 115 octane aviation fuel in my lawnmower.

Mind boggling.

I suggest you learn how an engine works, and then get back to us.

 

[Pacfanweb]

Originally posted by: RobCur
funny, how no one seem to know why their are 3 grades? yet you ali,say its different octane level well duh! which is 3 different quality(same thing, worded differently!). all car manual says unleaded fuel, not plus or premium. Its a matter of choice and preferences..
Why use lowest octane on a weak car??? it does not make sense to pay less for a very fuel efficent car like volkswagon etc or any small engine.
this arguement is getting pointless.es.s.s buy whatever you want and say whatever you like.. end of discusssiosns.s

1. Re: 3 grades of gas: Can you say, "Sales Tactic?"
2. Re: All car manuals say unleaded, not premium or plus: Can you say, "I'm WRONG"?
3. Re: Why use lowest octane on a weak car?: Can you say "Because the manual says so, and octane is NOT the reason the car is weak?"
4. Re: It's a matter of choice and preferences: Yes, it is...the preference the engineers who designed your car made, not YOUR preferences.

 

[Eli]

Originally posted by: Jeff7181

Originally posted by: Eli

Originally posted by: 0roo0roo

So basically you're saying you can use whatever gasoline you want because the ECU will completely remap the spark curve, from idle to redline, getting the most power you possibly can out of the engines design and the fuel it's using?

i dunno, but based on what has been said so far, why not? it'll damage the engine, but it'll work

Well, it shouldn't hurt anything as long as the system is indeed keeping it from knocking, but I just had no idea that the spark advance on an A-B econobox would do something like that.. at least to that extent.

I am still a little confused though, and I think maybe the Japanese makers do it differently, due to the quote from that Toyota PDF...

Did you miss the quote from Chapter 16 of that book?

I read that PDF 4 or 5 times, and the only way I could get what you're saying out of it is if I inferred what they meant.

An inference is not fact.

Again, from that PDF.

The ECM determines proper spark timing by applying various input signals against a preprogrammed spark advance strategy, or "map".

If you take the quote, "The spark advance program is designed to provide the maximum spark possible, while keeping the engine from producing an audible "ping"." in context with the above quote, there is a pre-set range, based on the engines design parameters, including but not limited to the octane it was designed to use. The ECM is free to modify the timing within this range as it sees fit.

If you take it out of context, you arrive at your conclusion, which I still believe is for the most part incorrect. Remember that we are lumping all cars from all manufacturers into one here, which isn't a good thing.

Knock sensor (KS) Circuit
An engine can withstand a small amount of spark knock for a short time, and this computer factors that into its spark advance calculations. The knock sensor must report a detonation event lasting longer than 99.99 milliseconds for 3 continuous cycles. The response then is to retard spark until the knock disappears. The basic ignition (spark advance) map for the engine assumes a fuel with an octane equivalence of 87, but the system can manipulate spark (more or less advanced) to accommodate a higher or lower detonation resistance with different fuels. In general, the system will drive the spark advance right to the edge of knock to maximize the fuel economy and reduce emissions problems.

It does appear that GM cars do what he says.

Are you sure that quote in the book pertains to all recent GM products? Do all GM products require 87 octane?

Also note that it says, "In general, the system will drive the spark advance right to the edge of knock..". In general being the key word.

I still contend that putting Premium in a car that was designed for Regular will not cause the ECU to advance the timing beyond the maximum that it was programmed to do[with the fuel the engine was designed to use], perhaps unless the car is a GM product. That method is an interesting way of approaching the whole thing, and I guess it makes sense from a performance standpoint, so maybe other auto manufacturers will(or already have) adopted this method. The key being that the "map" is designed around 87 octane, regardless of the engines requirements, and the ECU is free to modify it in any way it needs to.

We will figure this out.

 

[Zenmervolt]

Originally posted by: Slickone
I didn't say forums are where I got all my info. I know there are many clueless people in forums. Many in this thread (not referring to you).
BTW, calling someone's information bullsh!t is pretty immature. How old are you?
BTW, what happens when you use jet fuel in a piston engine? What happens when you use gasoline in a gas turbine engine?


This isn't an article I've seen before and isn't 'the article' that made my mind up. I don't know who this is. Anyway it says:

As to usability in a motor, ultra-high numbers are questionable. Octane will make up for some sins that an engine builder might have built into the motor, but an engine only needs what it needs... not a bit more.

Also:

TOO MUCH OCTANE CAN BE BAD!
Right now in the racing fuel business, there's a race to market the highest octane fuel that you can make. People relate the highest octane to "my motor is making more power." That couldn't be further from the truth.
One of the downsides to building a fuel with ultra-high octane is adding components that really slow down the flame front in the combustion process. You can get the flame front so slow, that the engine is now running in a too-rich condition. This takes away horsepower. So here you are, slowing down the flame front and getting rid of detonation, at the expense of losing horsepower.

BTW, that's "harm".

You prove my point. The article deals with a carburetored engine designed for high-RPM operation. Carburetors are notoriously awful at fuel metering. Any modern fuel-injected engine with computer controls will adjust for the gasoline and lean out the mixture if the burn is incomplete.

I never said that it could not cause problems, I said that if a stoichiometric mixture is maintained it cannot cause problems. That assumes that there is an adjustment to the mixture in order to maintain complete burn. If the engine is running rich, it's running rich and that's the problem. Regardless of whether the fuel is causing the rich condition or not, it's the rich condition and not the fuel that is causing the carbon deposits. Again, in modern, computer-controlled engines with fuel injection the mixture is adjusted and there is no problem with deposit formation. This assumes that all componants (especially the oxygen sensor) are functioning properly.

I've had my opinions called bullsh!t by my best friends, my worst enemies, people twice my age, people half my age, people I know, and people I don't know. If someone calling your information bullsh!t is offensive to you, I suggest that you grow a thicker skin because you're going to be offended a hell of a lot in this world unless you learn that not every colloquial use of swearing is a personal attack. As for my age, old enough to know what's right and young enough not to choose it.

ZV

 

[Pacfanweb]

Eli, there is a limit to how far a GM will advance.....it isn't infinite.

My 99 Tahoe will slightly knock, occasionally, on 87, which it's designed for. I can hear a few pings, then it retards. Doesn't just sit there and rattle, which is exactly what the knock sensor is for.

If I put 89 or 93 in, not only do I not feel a difference, but there is no spark knock. Ever. If the ECM advances the timing to the "edge of spark knock", why don't I hear at least a ping or two before it retards it?

Answer: Because it isn't capable of advancing the timing that high. That's why you have all the chips and programmers in the aftermarket, so you can jack the timing up like you used to do by turning the distributor back a few years ago.

Regarding this quote:

In general, the system will drive the spark advance right to the edge of knock to maximize the fuel economy and reduce emissions problems.

Notice the "in general". What that doesn't say is, "within the preprogrammed limits".
Which means you can't just drop some 100+ octane fuel and count on the ECM to push the timing up to the 38-40 degrees of timing you'd need to take advantage of such an octane.
Which means, as we've been asserting, premium is a waste unless your car calls for it.

 

[Eli]

Originally posted by: Pacfanweb
Eli, there is a limit to how far a GM will advance.....it isn't infinite.

My 99 Tahoe will slightly knock, occasionally, on 87, which it's designed for. I can hear a few pings, then it retards. Doesn't just sit there and rattle, which is exactly what the knock sensor is for.

If I put 89 or 93 in, not only do I not feel a difference, but there is no spark knock. Ever. If the ECM advances the timing to the "edge of spark knock", why don't I hear at least a ping or two before it retards it?

Answer: Because it isn't capable of advancing the timing that high. That's why you have all the chips and programmers in the aftermarket, so you can jack the timing up like you used to do by turning the distributor back a few years ago.

Regarding this quote:

In general, the system will drive the spark advance right to the edge of knock to maximize the fuel economy and reduce emissions problems.

Notice the "in general". What that doesn't say is, "within the preprogrammed limits".
Which means you can't just drop some 100+ octane fuel and count on the ECM to push the timing up to the 38-40 degrees of timing you'd need to take advantage of such an octane.
which means, as we've been asserting, premium is a waste unless your car calls for it.

Yep, I completely agree, and that is the way I understand it.

It does say that the map assumes 87 octane. Are there GM cars that require above 87 octane? If not, then.. yeah.

If there are.. what the hell is the point in that? heh.

 

[Pacfanweb]

I guess the Vette, and maybe some of the other performance rides, maybe that new/old truck thing, or the GTO?
I'm sure there are a few.

I'll tell you a funny/sad story: The dealership I worked for until 3 weeks ago (went in business for myself) sells Saleens.
Saleen puts a custom program in the PCM, which requires premium gas. Jacks the timing up. A stock Mustang GT requires 87.

So, some dumbass salesman sells one, and someone took it to fill it up.....and filled it with regular. Spark knocked TERRIBLY.
The equally dumbass customer proceeds to drive it home to Pinehurst, NC, from Raleigh NC. About an hour drive, if that much.
Doesn't even make it out of town....the engine is toast.
The kicker: The general sales manager is the one who filled it for him. DOH!!

 

[Eli]

Originally posted by: Pacfanweb
I guess the Vette, and maybe some of the other performance rides, maybe that new/old truck thing, or the GTO?
I'm sure there are a few.

I'll tell you a funny/sad story: The dealership I worked for until 3 weeks ago (went in business for myself) sells Saleens.
Saleen puts a custom program in the PCM, which requires premium gas. Jacks the timing up. A stock Mustang GT requires 87.

So, some dumbass salesman sells one, and someone took it to fill it up.....and filled it with regular. Spark knocked TERRIBLY.
The equally dumbass customer proceeds to drive it home to Pinehurst, NC, from Raleigh NC. About an hour drive, if that much.
Doesn't even make it out of town....the engine is toast.
The kicker: The general sales manager is the one who filled it for him. DOH!!

Ouch.

So the ECU won't even retard timing to the point of no knock if it isn't programmed to go down that far, heh.

So basically, it isn't infinately variable.

 

[Pacfanweb]

Exactly.

BTW, regarding Smokey Yunick, I remember reading about some type of fuel mixer, he called it a "homogenizer" that it seems like he put on a Plymouth Horizon back in the 80's.

It was supposed to be really efficient, and also produce ridiculous amounts of power.

Ever read about it? I think one of the car manufacturers bought the patent.

And I know this isn't a myth because I had the magazine with him and the car, explaining what it does.

 

[Eli]

Originally posted by: Pacfanweb
Exactly.

BTW, regarding Smokey Yunick, I remember reading about some type of fuel mixer, he called it a "homogenizer" that it seems like he put on a Plymouth Horizon back in the 80's.

It was supposed to be really efficient, and also produce ridiculous amounts of power.

Ever read about it? I think one of the car manufacturers bought the patent.

And I know this isn't a myth because I had the magazine with him and the car, explaining what it does.

Nope, I neverr read about that.

I was talking about something different. I still have the magazine around here somewhere, I'll have to see if I can find it. I was just referring to WO's post about the oil companies buying off his efficient engine. It was all about increasing the operating temperature of the engine, so as not to lose so much efficiency through heat.

 

[Eli]

Originally posted by: Jeff7181
*EDIT Whether 92 octane is worth the price difference is debatable.

Lets say you get 28 mpg on 87 octane, and 87 octane costs $1.70 per gallon, and your tank holds 15 gallons. That means you can drive 420 miles on $25.50 worth of gas. You end up getting 16.47 miles per dollar of fuel.

Now lets say you get 32 mpg on 92 octane, and 92 octane costs $2.00 per gallon, your tank still holds 15 gallons. That means you can drive 480 miles on $30 worth of gas. You end up getting 16 miles per dollar of fuel.

So 87 octane is still your best bet in this case... which by the way is a real example. On my way down to Florida in a 2001 Sable with Ford's 3.0L DOHC 24 valve V6 I ran 87 octane and got 28 mpg on the expressway. Once I got there I started putting premium fuel in it, 92 octane. And after a week of running it on that, when I drove back I kept using 92 octane and got 32 mpg. Wasn't worth it based on my calculations... but it was interesting to see a 4 mpg increase just by switching the grade of fuel.

~1mpg is a reasonable margin of error, and the other 3mpg could be attributed to something as seemingly insignificant as a tail wind.

Too many variables to be calling MPG differences between fuel grades, especially if you got the blend from a different station in a different region.... at least, IMO.