The performance cars like Preludes say on the dash board to use only Premium fuel

[LovingPerson]

Dear all:

My Prelude says on the dash board to use only premium fuel. That is the fuel I have been using. However, the previous owner says that she uses regular normal 87 octane without problem.

Is it okay for me to not use premium fuel? The way I understand it is that the higher octane is used so that higher compression engines do not experience pre-mature ignition. I also seem to remember from another source that the higher octane prevents Knocking. I am wondering if Knocking is the same as premature ignition.

Could someone tell me if it will be okay to use regular in my Prelude? Sincerely. Thx in advance.

 

[E. Meyer]

Dear all:

My Prelude says on the dash board to use only premium fuel. That is the fuel I have been using. However, the previous owner says that she uses regular normal 87 octane without problem.

Is it okay for me to not use premium fuel? The way I understand it is that the higher octane is used so that higher compression engines do not experience pre-mature ignition. I also seem to remember from another source that the higher octane prevents Knocking. I am wondering if Knocking is the same as premature ignition.

Could someone tell me if it will be okay to use regular in my Prelude? Sincerely. Thx in advance.

Knocking is the gas exploding rather than burning. It is sometimes called premature detonation, though that term literally means it goes off too soon, while the piston is still compressing, rather than at top-dead-center.

The higher octane in premium fuel resists knocking. Actually, that is the only benefit to premium fuel.

Modern cars use feedback from a knock detector and adjust the spark dynamically to minimize the problem. IF you read your owners manual, it probably says something along the lines of "... use premium fuel, but if it is not available, you can use fuel rated at least 87 with reduced performance".

As long as your knock detector is working, you can try it with regular and see what happens. If you start hearing knocking (pinging), or if your gas mileage drops significantly, that means the engine is making dramatic adjustments to accommodate the lower octane fuel (or the knock sensor doesn't work) and you should switch back to premium.

 

[Scott in Aztlán]

Could someone tell me if it will be okay to use regular in my Prelude?

I thought you said you didn't drive it, and it just sits in your carport, and that you were selling it?

 

[John Ings]

My Prelude says on the dash board to use only premium fuel. That is the fuel I have been using. However, the previous owner says that she uses regular normal 87 octane without problem.

Is it okay for me to not use premium fuel?

If you don't mind loosing performance. Using lower octane fuel than recommended used to be disasterous, but modern engines have knock sensors that will retard the ignition to compensate for lower octane. You won't get all the power you could be getting however.

The way I understand
it is that the higher octane is used so that higher compression engines do not experience pre-mature ignition.
Pre-ignition.

I also seem to
remember from another source that the higher octane prevents Knocking. I am wondering if Knocking is the same as premature ignition.
Essentially.

Could someone tell me if it will be okay to use regular in my Prelude?

http://www3.telus.net/public/johnings/faq.html#premium

 

[Paul Bielec]

If you don't mind loosing performance. Using lower octane fuel than recommended used to be disasterous, but modern engines have knock sensors that will retard the ignition to compensate for lower octane. You won't get all the power you could be getting however.

It will ADVANCE, not delay the ignition. The knock is produced when the mixture self ignites. In other words, higher the octane, higher the compression the fuel mixture can sustain without self igniting.

 

[John Ings]

It will ADVANCE, not delay the ignition.

Will retard the ignition. In other words delay the firing of the spark plug.

The knock is produced when the mixture self ignites.
In other words, higher the octane, higher the compression the fuel mixture can sustain without self igniting.

Correct. And the more ignition advance the engine can handle. e.g. http://www.jcna.com/library/tech/tech0013.html

 

[Paul Bielec]

Will retard the ignition. In other words delay the firing of the spark plug.

No, it will advance the ignition to fire up the mixture before it self-ignites. This reduces the performance of the engine because the ignition happens before the highest compression ratio is achieved. But it forces the mixture explosion to happen correctly i.e. from the top of the cylinder pushing down on the piston. While the self-ignition can happen anywhere in the combustion chamber and the forces will push excessively against the cylinder walls and the valves instead of pushing mostly downward on the piston. This reminds me the way they used to destroy cannons centuries ago. They would place a bag with gun powder at the cannon's opening. The force of the explosion pushing down the cannon towards its dead end would brake the metal.

 

[Stephen Bigelow]

No, it will advance the ignition to fire up the mixture before it self-ignites. This reduces the performance of the engine because the ignition happens before the highest compression ratio is achieved.

I see.
So what is the optimum ignition timing?
Fixed at TDC?

 

[John Ings]

No, it will advance the ignition to fire up the mixture before it self-ignites.

Self ignition will never occur at the low compression ratios found in gasoline engines.

This reduces the performance of the engine because the ignition happens before the highest compression ratio is achieved.

You haven't a clue what you're talking about sonny!

But it forces the mixture explosion to happen correctly i.e. from the top of the cylinder pushing down on the piston.

While the piston is still on it's way up? Baloney.
Here is a good online course. Go do your homework:
http://www.centuryperformance.com/timing.asp

While the self-ignition can happen
anywhere in the combustion chamber and the forces will push excessively against the cylinder walls and the valves instead of pushing mostly downward on the piston.

Drivel. Any combustion or explosion occuring in a cylinder acts equally in all directions. It's not a shaped charge,

This reminds me the way they used to destroy cannons centuries ago. They would place a bag with gun powder at the cannon's opening. The force of the explosion pushing down the cannon towards its dead end would brake the metal.

Nonsense.

You're as confused as a bottle baby in a topless bar kid!

 

[Paul Bielec]

Here is a good online course. Go do your homework.

First hint for you. Open www.google.com and type in:
"what is engine knock?"

You'll get a definition, as well as plenty of articles to educate yourself on the subject.

You'll learn that, even in a gasoline engine, an auto ignition can happen, especially around the edges of the piston. The causes are mostly gasoline with too low octane factor or combustion soot deposits inside the cylinders. This will cause an undesired flame front, which will travel in wrong direction. In extreme cases (engines with no knock sensor), it may even bend the piston rod if the detonation happens early in the stroke, while the piston is still travelling up. These undesired detonations will cause vibrations, which will be detected by the knock sensor. The ECU will then advance the ignition.

Of course, the vibration can be a result of badly adjusted ignition timing (engine mods, modified program, fine tunning of racing cars etc.), but this is a whole different story and has nothing to do with using regular gas instead of high octane gas. In this case, it is the spark plus that lights up the fuel at a wrong moment (too early, while the piston is still travelling up) and the ignition has to be retarded to correct the problem.

Before calling someone a "kid" or "sonny", you should learn a little about what you're talking about.

Paul Bielec, B. Eng.

 

[Paul Bielec]

I see.
So what is the optimum ignition timing?
Fixed at TDC?

The software in the ECU will trigger the ignition based on several parameters. The software will vary from one car/engine to another. Ideally, you'd want the ignition to happen when the piston has travelled all the way up and the fuel mixture is at its higher pressure. In practice, it will probably happen when the piston just started travelling down, just a guess.

 

[Stephen Bigelow]

The software in the ECU will trigger the ignition based on several parameters.
Uh-huh.

The software will vary from one car/engine to another.

I see.

Ideally, you'd want the ignition to happen when the piston has travelled all the way up and the fuel mixture is at its higher pressure. In practice, it will probably happen when the piston just started travelling down, just a guess.

I see.
Have you ever set ignition timing on an engine?
What is the base timing for *your* car, Paul?

 

[Paul Bielec]

Have you ever set ignition timing on an engine?

What is the base timing for *your* car, Paul?

Nope, never changed the timing on any of my cars. Never changed the chip. I was always happy with the OEM computer. On the other hand, back at university, several of my friends were involved in the Formula SAE project. They were designing an engine cotroller unit for their car. The ECU software was written by the students, members of the project.

Today, I'm involved with engine controller software but it is not for internal combustion engines.

I was involved in coding of the software for the following engines:
http://www.gepower.com/prod_serv/products/aero_turbines/en/lm2500.htm http://www2.rolls-royce.com/menu.nsf/wwwprint?openagent&Area=About+MarineRol ls-Royce+plc*Marine&Docid=78F73067FF03F5BAC12569F1004CB152

Not quiet the same power output.

 

[Stephen Bigelow]

Nope, never changed the timing on any of my cars. Never changed the chip. I was always happy with the OEM computer.

That wasn't the question.
What is the base timing for your car?

 

[JRK]

Self ignition will never occur at the low compression ratios found in gasoline engines.

You haven't a clue what you're talking about sonny!

While the piston is still on it's way up? Baloney.
Here is a good online course. Go do your homework:
http://www.centuryperformance.com/timing.asp

That's funny! The site you reference describes setting the timing to fire on the way up for performance.

 

[Stephen Bigelow]

top

That's funny! The site you reference describes setting the timing to fire on the way up for performance.

Gee...you mean before top dead centre?

Amazing!

 

[Paul Bielec]

chip.

That wasn't the question.
What is the base timing for your car?

I don't know.

 

[Casey]

John Ings said...

You haven't a clue what you're talking about sonny!

Funny how saying things like this will often come back to haunt you.

While the piston is still on it's way up? Baloney.
Here is a good online course. Go do your homework:
http://www.centuryperformance.com/timing.asp

Did you bother to read it? You might actually learn something.

I'm guessing you never used a timing light and a dwell meter on a older "non-electronic ignition" engine...

Casey

"It is easier to get older than it is to get wiser."

 

[Matthew Russotto]

You'll learn that, even in a gasoline engine, an auto ignition can happen, especially around the edges of the piston. The causes are mostly gasoline with too low octane factor or combustion soot deposits inside the cylinders. This will cause an undesired flame front, which will travel in wrong direction. In extreme cases (engines with no knock sensor), it may even bend the piston rod if the detonation happens early in the stroke, while the piston is still travelling up. These undesired detonations will cause vibrations, which will be detected by the knock sensor. The ECU will then advance the ignition.

Retard. Knock sensors retard the ignition. Always.

 

[John Ings]

First hint for you. Open www.google.com and type in:
"what is engine knock?"

You'll get a definition, as well as plenty of articles to educate yourself on the subject.

Indeed. Such as this one: http://www.jandssafeguard.com/ Note the first sentence in the second paragraph:
"Using a single knock sensor, the system detects the onset of detonation and RETARDS the timing on a per cylinder basis"

Or this one: http://focus.ti.com/docs/prod/folders/print/tpic8101.html on a knock sensor chip from Texas Instruments. Note the line midway down the page:

"The data from the A/D enables the system to analyze the amount of RETARD timing for the next spark ignition timing cycle."

You'll learn that, even in a gasoline engine, an auto ignition can happen, especially around the edges of the piston. The causes are mostly gasoline with too low octane factor or combustion soot deposits inside the cylinders. This will cause an undesired flame front, which will travel in wrong direction. In extreme cases (engines with no knock sensor), it may even bend the piston rod if the detonation happens early in the stroke, while the piston is still travelling up. These undesired detonations will cause vibrations, which will be detected by the knock sensor.

All correct so far.

The ECU will then advance the ignition.

No, it will retard the ignition.

Of course, the vibration can be a result of badly adjusted ignition timing (engine mods, modified program, fine tunning of racing cars etc.), but this is a whole different story and has nothing to do with using regular gas instead of high octane gas. In this case, it is the spark plus that lights up the fuel at a wrong moment (too early, while the piston is still travelling up)

Most cars fire the plug when the piston is on the way up, unless the engine is very large and runs at low RPM.

and the ignition has to be retarded to correct the problem.

Before calling someone a "kid" or "sonny", you should learn a little about what you're talking about.

I've been setting the timing on cars for 48 years SONNY.
And you're full of shit.

Paul Bielec, B. Eng.

Generally as soon as a junior engineer shows up on the shop floor, the foreman sends a tech to keep an eye on him and make sure he doesn't get into trouble.