regular vs. premium gasoline?

[Eli]

Originally posted by: galvanizedyankee
A layer of carbon can provide some insulation, a heat barrier of sorts. There would be less heat loss into the head and piston so there would be a slight net gain in HP.

Racers are known to treat the cooling passages of aluminum heads with chemicals so the alloy doesn't suck off too much heat. Put too thick of a coating on and it will move into pre-ignition. The famous Smokey was one of the first to do this. If your interested in it Eli, I will PM you the books ISBN#.

Smokey rules! I used to love his Popular Mechanics articles and Q/A.

I wonder whatever hapened to that ultra-efficient engine he was building in the late 80s? He had a working prototype, it used ceramics and special alloy metals to raise the coolant operating temperature to ~300F, IIRC.

It's been a while since I read about it. It must not have been anything too earth shattering, or we would see that sort of technology in use today..

 

[RobCur]

For some who disagree with me, would it make sense to use to most expensive fuel on a V8 engine, guggling up so much gas? it wouldn't help much either cause the engine is already powerful enough as is.. A weak car like my puny truck mazda b2200 of V4, 85 HR PWR benefitly greatly from premium gas then regular or middle grade, plus when I do that, my engine is weak and gets cut off alot. Today's new car is V6, so I recommend it is best to use unleaded plus.

 

[WinkOsmosis]

Originally posted by: Eli

Originally posted by: galvanizedyankee
A layer of carbon can provide some insulation, a heat barrier of sorts. There would be less heat loss into the head and piston so there would be a slight net gain in HP.

Racers are known to treat the cooling passages of aluminum heads with chemicals so the alloy doesn't suck off too much heat. Put too thick of a coating on and it will move into pre-ignition. The famous Smokey was one of the first to do this. If your interested in it Eli, I will PM you the books ISBN#.

Smokey rules! I used to love his Popular Mechanics articles and Q/A.

I wonder whatever hapened to that ultra-efficient engine he was building in the late 80s? He had a working prototype, it used ceramics and special alloy metals to raise the coolant operating temperature to ~300F, IIRC.

It's been a while since I read about it. It must not have been anything too earth shattering, or we would see that sort of technology in use today..

Oil companies bought it.

 

[Eli]

Originally posted by: RobCur
For some who disagree with me, would it make sense to use to most expensive fuel on a V8 engine, guggling up so much gas? it wouldn't help much either cause the engine is already powerful enough as is.. A weak car like my puny truck mazda b2200 of V4, 85 HR PWR benefitly greatly from premium gas then regular or middle grade, plus when I do that, my engine is weak and gets cut off alot. Today's new car is V6, so I recommend it is best to use unleaded plus.

Dear Lord, you haven't the slightest clue about what you're talking about, do you? First, your B2200 uses an I4, not a V4.. lol

Educate yourself. Read through this thread again. Please.

And just FYI, the high performance V8 in my pickup requires Plus, because of its 10.5:1 compression ratio.

The size of the engine has nothing to do with it. There are 4 cylinder engines that require Regular, and there are 8 cylinder engines that require Premium.

And once again, for all intents and purposes, there is no difference between the different grades of gasoline except price and octane(resistance to spontaneous ignition). It has nothing to do with quality, or performance.

It's almost mind boggling that someone can be so incredibly misinformed.

 

[Calin]

While using premium octane fuel in my car, I felt a bit more power. And switching back, it was a bit slower. Subjective only, I have no idea why or even if it the feeling was created by my expectation...

Anyway, I use now the fuel specified by the car, and it works ok

Calin

 

[Eli]

Originally posted by: Calin
While using premium octane fuel in my car, I felt a bit more power. And switching back, it was a bit slower. Subjective only, I have no idea why or even if it the feeling was created by my expectation...

Anyway, I use now the fuel specified by the car, and it works ok

Calin

It's allll in your head..

It's easy to do. You don't pay much attention to the cars power, but all of a sudden you do.. and you notice every little bit of it, and of course you attribute it to the new gasoline you thought you'd try.

Unless your car is designed to take premium, and you're putting regular in it. That can definately have a negative impact on performance, because the ECU will retard timing if it detects detonation. Refilling with Premium would fix the problem.

 

[Eli]

Originally posted by: WinkOsmosis

Originally posted by: Eli

Originally posted by: galvanizedyankee
A layer of carbon can provide some insulation, a heat barrier of sorts. There would be less heat loss into the head and piston so there would be a slight net gain in HP.

Racers are known to treat the cooling passages of aluminum heads with chemicals so the alloy doesn't suck off too much heat. Put too thick of a coating on and it will move into pre-ignition. The famous Smokey was one of the first to do this. If your interested in it Eli, I will PM you the books ISBN#.

Smokey rules! I used to love his Popular Mechanics articles and Q/A.

I wonder whatever hapened to that ultra-efficient engine he was building in the late 80s? He had a working prototype, it used ceramics and special alloy metals to raise the coolant operating temperature to ~300F, IIRC.

It's been a while since I read about it. It must not have been anything too earth shattering, or we would see that sort of technology in use today..

Oil companies bought it.

meh.. my sarcasm meter is broken, you being serious? cause..

you can't patent metal and ceramics, let alone across the globe.. lol

If the technology was available to him, it's available to everyone..... especially the R&D departments of multi-billion dollar corporations on the cutting edge of engine technology .....

 

[AlienCraft]

Originally posted by: Eli

Originally posted by: Calin
While using premium octane fuel in my car, I felt a bit more power. And switching back, it was a bit slower. Subjective only, I have no idea why or even if it the feeling was created by my expectation...

Anyway, I use now the fuel specified by the car, and it works ok

Calin

It's allll in your head..

It's easy to do. You don't pay much attention to the cars power, but all of a sudden you do.. and you notice every little bit of it, and of course you attribute it to the new gasoline you thought you'd try.

Unless your car is designed to take premium, and you're putting regular in it. That can definately have a negative impact on performance, because the ECU will retard timing if it detects detonation. Refilling with Premium would fix the problem.

Exactly. This is why a car seems to "drive better" after a good cleaning and maintenance.

 

[0roo0roo]

you people suck

http://auto.howstuffworks.com/question90.htm

DO NOT buy high octane unless specified. 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.


If you've read How Car Engines Work, you know that almost all cars use four-stroke gasoline engines. One of the strokes is the compression stroke, where the engine compresses a cylinder-full of air and gas into a much smaller volume before igniting it with a spark plug. The amount of compression is called the compression ratio of the engine. A typical engine might have a compression ratio of 8-to-1. (See How Car Engines Work for details.)

The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.

The compression ratio of your engine determines the octane rating of the gas you must use in the car. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel. The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight -- that is what makes the engine "high performance." The disadvantage is that the gasoline for your engine costs more.

The name "octane" comes from the following fact: When you take crude oil and "crack" it in a refinery, you end up getting hydrocarbon chains of different lengths. These different chain lengths can then be separated from each other and blended to form different fuels. For example, you may have heard of methane, propane and butane. All three of them are hydrocarbons. Methane has just a single carbon atom. Propane has three carbon atoms chained together. Butane has four carbon atoms chained together. Pentane has five, hexane has six, heptane has seven and octane has eight carbons chained together.

It turns out that heptane handles compression very poorly. Compress it just a little and it ignites spontaneously. Octane handles compression very well -- you can compress it a lot and nothing happens. Eighty-seven-octane gasoline is gasoline that contains 87-percent octane and 13-percent heptane (or some other combination of fuels that has the same performance of the 87/13 combination of octane/heptane). It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio.

During WWI, it was discovered that you can add a chemical called tetraethyl lead to gasoline and significantly improve its octane rating. Cheaper grades of gasoline could be made usable by adding this chemical. This led to the widespread use of "ethyl" or "leaded" gasoline. Unfortunately, the side effects of adding lead to gasoline are:

* Lead clogs a catalytic converter and renders it inoperable within minutes.
* The Earth became covered in a thin layer of lead, and lead is toxic to many living things (including humans).

When lead was banned, gasoline got more expensive because refineries could not boost the octane ratings of cheaper grades any more. Airplanes are still allowed to use leaded gasoline, and octane ratings of 115 are commonly used in super-high-performance piston airplane engines (jet engines burn kerosene, by the way).

 

[Nebor]

Oh man, so with my Lighting, not only do I get like 10mpg, but the premium gasoline is an extra kick in the balls for the environment? Bwahahahaha. That's hilarious.

 

[Eli]

Originally posted by: Nebor
Oh man, so with my Lighting, not only do I get like 10mpg, but the premium gasoline is an extra kick in the balls for the environment? Bwahahahaha. That's hilarious.

??

It's no worse than Regular.

The article on howitworks was talking about when we used tetra ethyl lead instead of MTBE and ethanol to raise the octane of our gasoline.

 

[Nebor]

Well, I didn't really read what orooroo posted, but I assumed it was saying that higher octane is worse for the planet.

Shucks, I guess I'll just have to pour my used motor oil in the gutter.

 

[Eli]

Originally posted by: Nebor
Well, I didn't really read what orooroo posted, but I assumed it was saying that higher octane is worse for the planet.

Shucks, I guess I'll just have to pour my used motor oil in the gutter.

hmm.. heh..

My sarcasm meter is still broken, I guess.. lol

 

[Jeff7181]

Originally posted by: fyleow

Originally posted by: Wheatmaster

Originally posted by: fyleow

Originally posted by: Crappopotamus
ive been filling the max with regular gas for its whole life. i heard that you should fill it with premium, or it will knock, and permanently damage the engine and or trigger the knock sensor, which will make the engine automatically scale down. oh well. :|

and if higher octane fuel is less powerful, why do people fill up with premium before hitting the racetrack?

Read the thread, high performance engines need high octane fuel or they will knock.

so most sedans like honda accord and ford taurus don't need premium fuel? why the heck do people buy it then?

It's all about the compression ratios. If your car manual says to use regular unleaded then just use that and don't worry about it.

This is what I was told in college...

The reason people use higher octane fuel before "hitting the racetrack" is because higher octane fuel allows you to run more spark advance, which will make more power. With computer controlled distributorless ignitions, the change is automatic... the computer advances the spark until it detects pinging via the knock sensor, then it retards timing till it goes away, then it advances till it appears again, etc. etc. With old distributor ignitions, people will fill up with high octane fuel, then turn the distributor to give it a few more degrees of advance.

 

[Eli]

Originally posted by: Jeff7181

Originally posted by: fyleow

Originally posted by: Wheatmaster

Originally posted by: fyleow

Originally posted by: Crappopotamus
ive been filling the max with regular gas for its whole life. i heard that you should fill it with premium, or it will knock, and permanently damage the engine and or trigger the knock sensor, which will make the engine automatically scale down. oh well. :|

and if higher octane fuel is less powerful, why do people fill up with premium before hitting the racetrack?

Read the thread, high performance engines need high octane fuel or they will knock.

so most sedans like honda accord and ford taurus don't need premium fuel? why the heck do people buy it then?

It's all about the compression ratios. If your car manual says to use regular unleaded then just use that and don't worry about it.

This is what I was told in college...

The reason people use higher octane fuel before "hitting the racetrack" is because higher octane fuel allows you to run more spark advance, which will make more power. With computer controlled distributorless ignitions, the change is automatic... the computer advances the spark until it detects pinging via the knock sensor, then it retards timing till it goes away, then it advances till it appears again, etc. etc. With old distributor ignitions, people will fill up with high octane fuel, then turn the distributor to give it a few more degrees of advance.

Just to clear it up, an engine's ECU will only advance the timing like that if it was specifically programmed to. Your Camry and Accord doesen't do that(stock). It has a set range.

 

[Jeff7181]

Originally posted by: Eli

Originally posted by: Jeff7181

Originally posted by: fyleow

Originally posted by: Wheatmaster

Originally posted by: fyleow

Originally posted by: Crappopotamus
ive been filling the max with regular gas for its whole life. i heard that you should fill it with premium, or it will knock, and permanently damage the engine and or trigger the knock sensor, which will make the engine automatically scale down. oh well. :|

and if higher octane fuel is less powerful, why do people fill up with premium before hitting the racetrack?

Read the thread, high performance engines need high octane fuel or they will knock.

so most sedans like honda accord and ford taurus don't need premium fuel? why the heck do people buy it then?

It's all about the compression ratios. If your car manual says to use regular unleaded then just use that and don't worry about it.

This is what I was told in college...

The reason people use higher octane fuel before "hitting the racetrack" is because higher octane fuel allows you to run more spark advance, which will make more power. With computer controlled distributorless ignitions, the change is automatic... the computer advances the spark until it detects pinging via the knock sensor, then it retards timing till it goes away, then it advances till it appears again, etc. etc. With old distributor ignitions, people will fill up with high octane fuel, then turn the distributor to give it a few more degrees of advance.

Just to clear it up, an engine's ECU will only advance the timing like that if it was specifically programmed to. Your Camry and Accord doesen't do that(stock). It has a set range.

Actually... every modern computer controlled car has the capability to adjust timing... it doesn't care if it needs to do it because of the fuel you're using or the load on the engine... it just does it. It's part of the emission controls.

 

[Eli]

Originally posted by: Jeff7181

Originally posted by: Eli

Originally posted by: Jeff7181

Originally posted by: fyleow

Originally posted by: Wheatmaster

Originally posted by: fyleow

Originally posted by: Crappopotamus
ive been filling the max with regular gas for its whole life. i heard that you should fill it with premium, or it will knock, and permanently damage the engine and or trigger the knock sensor, which will make the engine automatically scale down. oh well. :|

and if higher octane fuel is less powerful, why do people fill up with premium before hitting the racetrack?

Read the thread, high performance engines need high octane fuel or they will knock.

so most sedans like honda accord and ford taurus don't need premium fuel? why the heck do people buy it then?

It's all about the compression ratios. If your car manual says to use regular unleaded then just use that and don't worry about it.

This is what I was told in college...

The reason people use higher octane fuel before "hitting the racetrack" is because higher octane fuel allows you to run more spark advance, which will make more power. With computer controlled distributorless ignitions, the change is automatic... the computer advances the spark until it detects pinging via the knock sensor, then it retards timing till it goes away, then it advances till it appears again, etc. etc. With old distributor ignitions, people will fill up with high octane fuel, then turn the distributor to give it a few more degrees of advance.

Just to clear it up, an engine's ECU will only advance the timing like that if it was specifically programmed to. Your Camry and Accord doesen't do that(stock). It has a set range.

Actually...

Hmmmmmm....... After I re-read what I said, I figured it actually wouldnt clear anything up ... lol

I didn't find in there where it said that it will advance the timing all the way until knocking occours.. I mean, heh... I guess it implies it, but it also talks about the spark advance curve beforehand, so that also implies a set range..

There is a set range. The ECU might adjust the curve, but it will not go beyond the extremes of the curve.. unless programmed to?

An engine designed to run 87 octane with a spark advance curve that was designed for 87 octane at peak power output.. isn't going to advance the timing beyond that point and produce more horsepower than it was rated for, do you know what I mean? heh...

That is interesting, though. In theory, running Plus or Premium in a car with electronically controlled spark advance.. could modify the ECUs spark advance curve, compared to regular unleaded.. and therefor change the power curve of the engine... hmm.

I think we're just thinking on 2 different lines here. I know it will advance it until the point of knocking, but only within that specific map. If the engine was designed to run on 87 octane, the map will be designed for 87 octane. Putting Premium in the car isn't going to change the maximum spark advance the engine will see. I guess that's what I'm trying to say.. lol

 

[Jeff7181]

Originally posted by: Eli

Originally posted by: Jeff7181

Originally posted by: Eli

Originally posted by: Jeff7181

Originally posted by: fyleow

Originally posted by: Wheatmaster

Originally posted by: fyleow

Originally posted by: Crappopotamus
ive been filling the max with regular gas for its whole life. i heard that you should fill it with premium, or it will knock, and permanently damage the engine and or trigger the knock sensor, which will make the engine automatically scale down. oh well. :|

and if higher octane fuel is less powerful, why do people fill up with premium before hitting the racetrack?

Read the thread, high performance engines need high octane fuel or they will knock.

so most sedans like honda accord and ford taurus don't need premium fuel? why the heck do people buy it then?

It's all about the compression ratios. If your car manual says to use regular unleaded then just use that and don't worry about it.

This is what I was told in college...

The reason people use higher octane fuel before "hitting the racetrack" is because higher octane fuel allows you to run more spark advance, which will make more power. With computer controlled distributorless ignitions, the change is automatic... the computer advances the spark until it detects pinging via the knock sensor, then it retards timing till it goes away, then it advances till it appears again, etc. etc. With old distributor ignitions, people will fill up with high octane fuel, then turn the distributor to give it a few more degrees of advance.

Just to clear it up, an engine's ECU will only advance the timing like that if it was specifically programmed to. Your Camry and Accord doesen't do that(stock). It has a set range.

Actually...

Hmmmmmm....... After I re-read what I said, I figured it actually wouldnt clear anything up ... lol

I didn't find in there where it said that it will advance the timing all the way until knocking occours.. I mean, heh... I guess it implies it, but it also talks about the spark advance curve beforehand, so that also implies a set range..

There is a set range. The ECU might adjust the curve, but it will not go beyond the extremes of the curve.. unless programmed to?

An engine designed to run 87 octane with a spark advance curve that was designed for 87 octane at peak power output.. isn't going to advance the timing beyond that point and produce more horsepower than it was rated for, do you know what I mean? heh...

That is interesting, though. In theory, running Plus or Premium in a car with electronically controlled spark advance.. could modify the ECUs spark advance curve, compared to regular unleaded.. and therefor change the power curve of the engine... hmm.

I think we're just thinking on 2 different lines here. I know it will advance it until the point of knocking, but only within that specific map. If the engine was designed to run on 87 octane, the map will be designed for 87 octane. Putting Premium in the car isn't going to change the maximum spark advance the engine will see. I guess that's what I'm trying to say.. lol

I don't mean to be rude, but it's not a theory, it's fact. If you don't trust me I guess I could dig out my books from college later and scan the pages with information about this.

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

 

[NeoPTLD]

Gasoline FAQAll you ever need to know about gasoline. Read the whole thing. Come back and ask questions if there's anything not covered in there.

 

[Jeff7181]

I don't have my scanner hooked up so...

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.

page 215, Chapter 6: Recent General Motors' Engine Controls, Computerized Engine Controls, Fifth Edition 2001 Update, Dick H. King and Gary R. Watson, Copyright 2002 by Delmar/Thomas Learning

Here's another quote... same book, but page 462, Chapter 16: Asian Computer Control Systems

Knock Sensors

V-6 engines use two knock sensors, one on each bank, in-line engines use one. The knock sensor, as on other systems, is a piezoelectric design that, when vibrated at a frequency characteristic of knock, sends a signal to the computer, which then retards spark advance until the knock disappears. Spark advance is then readvanced until the knock reappears.

 

[Eli]

Originally posted by: Jeff7181

Originally posted by: Eli

Originally posted by: Jeff7181

Originally posted by: Eli

Originally posted by: Jeff7181

Originally posted by: fyleow

Originally posted by: Wheatmaster

Originally posted by: fyleow

Originally posted by: Crappopotamus
ive been filling the max with regular gas for its whole life. i heard that you should fill it with premium, or it will knock, and permanently damage the engine and or trigger the knock sensor, which will make the engine automatically scale down. oh well. :|

and if higher octane fuel is less powerful, why do people fill up with premium before hitting the racetrack?

Read the thread, high performance engines need high octane fuel or they will knock.

so most sedans like honda accord and ford taurus don't need premium fuel? why the heck do people buy it then?

It's all about the compression ratios. If your car manual says to use regular unleaded then just use that and don't worry about it.

This is what I was told in college...

The reason people use higher octane fuel before "hitting the racetrack" is because higher octane fuel allows you to run more spark advance, which will make more power. With computer controlled distributorless ignitions, the change is automatic... the computer advances the spark until it detects pinging via the knock sensor, then it retards timing till it goes away, then it advances till it appears again, etc. etc. With old distributor ignitions, people will fill up with high octane fuel, then turn the distributor to give it a few more degrees of advance.

Just to clear it up, an engine's ECU will only advance the timing like that if it was specifically programmed to. Your Camry and Accord doesen't do that(stock). It has a set range.

Actually...

Hmmmmmm....... After I re-read what I said, I figured it actually wouldnt clear anything up ... lol

I didn't find in there where it said that it will advance the timing all the way until knocking occours.. I mean, heh... I guess it implies it, but it also talks about the spark advance curve beforehand, so that also implies a set range..

There is a set range. The ECU might adjust the curve, but it will not go beyond the extremes of the curve.. unless programmed to?

An engine designed to run 87 octane with a spark advance curve that was designed for 87 octane at peak power output.. isn't going to advance the timing beyond that point and produce more horsepower than it was rated for, do you know what I mean? heh...

That is interesting, though. In theory, running Plus or Premium in a car with electronically controlled spark advance.. could modify the ECUs spark advance curve, compared to regular unleaded.. and therefor change the power curve of the engine... hmm.

I think we're just thinking on 2 different lines here. I know it will advance it until the point of knocking, but only within that specific map. If the engine was designed to run on 87 octane, the map will be designed for 87 octane. Putting Premium in the car isn't going to change the maximum spark advance the engine will see. I guess that's what I'm trying to say.. lol

I don't mean to be rude, but it's not a theory, it's fact. If you don't trust me I guess I could dig out my books from college later and scan the pages with information about this.

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

I do not believe that is correct, but I am completely willing to learn.. I guess I'm not understanding how this fits into things. Why even bother to have an octane recomendation at all?

Why don't all auto manufacturers recommend you use Premium, then, since that would result in the maximum advance possible, and the maximum output of the engine? What octane do they run the dyno tests at to arrive at the engines specs?

So you're saying that if you put 110 octane racing fuel into your Civic, the ECU will automatically advance the timing right up until the point that 110 octane fuel starts to detonate(well, assuming the engine is even capable of detonating the fuel.. lol)?

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?

That just doesen't jive with me. From that PDF you linked,

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.

Again, I could be way off base here..... but the way you're explaining it doesen't currently make sense to me.

Edit:

I re-read the quote from the GM book. It does say exactly that. That is quite interesting.

Are you sure the Japanese cars do the same thing? I mean, don't get me wrong.. It's a great feature, and it does indeed make sense.. in some ways, but.. hmm. Now I'm going to have to do a lot of research on this, just so I can clear it up within my own head, lol...

 

[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

 

[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...

 

[Pacfanweb]

Originally posted by: Jeff7181

Originally posted by: Eli

Originally posted by: Jeff7181

Originally posted by: Eli

Originally posted by: Jeff7181

Originally posted by: fyleow

Originally posted by: Wheatmaster

Originally posted by: fyleow

Originally posted by: Crappopotamus
ive been filling the max with regular gas for its whole life. i heard that you should fill it with premium, or it will knock, and permanently damage the engine and or trigger the knock sensor, which will make the engine automatically scale down. oh well. :|

and if higher octane fuel is less powerful, why do people fill up with premium before hitting the racetrack?

Read the thread, high performance engines need high octane fuel or they will knock.

so most sedans like honda accord and ford taurus don't need premium fuel? why the heck do people buy it then?

It's all about the compression ratios. If your car manual says to use regular unleaded then just use that and don't worry about it.

This is what I was told in college...

The reason people use higher octane fuel before "hitting the racetrack" is because higher octane fuel allows you to run more spark advance, which will make more power. With computer controlled distributorless ignitions, the change is automatic... the computer advances the spark until it detects pinging via the knock sensor, then it retards timing till it goes away, then it advances till it appears again, etc. etc. With old distributor ignitions, people will fill up with high octane fuel, then turn the distributor to give it a few more degrees of advance.

Just to clear it up, an engine's ECU will only advance the timing like that if it was specifically programmed to. Your Camry and Accord doesen't do that(stock). It has a set range.

Actually...

Hmmmmmm....... After I re-read what I said, I figured it actually wouldnt clear anything up ... lol

I didn't find in there where it said that it will advance the timing all the way until knocking occours.. I mean, heh... I guess it implies it, but it also talks about the spark advance curve beforehand, so that also implies a set range..

There is a set range. The ECU might adjust the curve, but it will not go beyond the extremes of the curve.. unless programmed to?

An engine designed to run 87 octane with a spark advance curve that was designed for 87 octane at peak power output.. isn't going to advance the timing beyond that point and produce more horsepower than it was rated for, do you know what I mean? heh...

That is interesting, though. In theory, running Plus or Premium in a car with electronically controlled spark advance.. could modify the ECUs spark advance curve, compared to regular unleaded.. and therefor change the power curve of the engine... hmm.

I think we're just thinking on 2 different lines here. I know it will advance it until the point of knocking, but only within that specific map. If the engine was designed to run on 87 octane, the map will be designed for 87 octane. Putting Premium in the car isn't going to change the maximum spark advance the engine will see. I guess that's what I'm trying to say.. lol

I don't mean to be rude, but it's not a theory, it's fact. If you don't trust me I guess I could dig out my books from college later and scan the pages with information about this.

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

WRONG, unless your vehicle is designed to run on premium. Totally wrong. Most cars, the total timing advance is around 30-32 degrees. Putting premium in your Taurus will NOT, repeat, will NOT under any circumstance make the computer jack any higher than it will with regular.

 

[Pacfanweb]

Eli, no standard car will just jack the timing up to the detonation point of any fuel you decide to put in it.

If you put 110 octane in a 9:1 compression Cavalier, the total timing could be probably 50 degrees and it wouldn't detonate.

And the ECM will NOT put the timing that high, there is a design limit just like you thought. It wouldn't run worth a damn with that much timing anyway.