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

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.

 

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

 

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.

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

 

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.

 

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

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

 

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.

 

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

 

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

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

Nonsense.

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

 

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.

 

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.

 

I see.

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

 

Have you ever set ignition timing on an engine?

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.

 

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

 

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!

 

I don't know.

 

John Ings said...

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

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."

 

Retard. Knock sensors retard the ignition. Always.

 

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."

All correct so far.

No, it will retard the ignition.

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

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

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.