87 octane '06 Sonata

I don't think fuel octane can have any bearing on the valve train. What you are hearing typically is detonation, commonly called "pinging." Typically, this will increase with more throttle at a given speed or at lower RPMs (lugging).

I have the 4 cylinder engine, but I have not noticed any problem as yet on standard 87 octane. Have you tried a different brand of fuel? I've found that not all brands are equal with regard to resistance to detonation.

Matt

I stick to "name brand" stations. (BP, Chevron and sometimes Racetrack) They all ping with 87 octane. Runs great on 89. No big deal its just Hyundai says

2. Rob

Well, it does cost several cents more per gallon so it may be a big deal over time. I specifically asked the salesman about this before buying my I4 Sonata and he said 87 was fine. So far, he has been right, however, pinging typically occurs during warmer weather and it hasn't been above 45 since I bought mine. July and August will be the test for me.

Matt

I think you guys need to move to the Midwest (NOT necessarily into a big city like Chicago, either).

In the Midwest, because of ethanol subsidies, 89 fuel is actually cheaper than 87, especially in states like Iowa and Illinois. I run all my vehicles on 89 out here. When I drive outside the midwest, they all run on 87 just fine.

In the Midwest, no dealer would be allowed to treat their customers the way some of you are treated at some of your dealerships. Since even Toyota and Honda still fight for recognition in these parts, you can be sure that customers for nameplates like Hyundai and Kia are going to be treated like kings and queens. Indeed, we would make sure these people would not even eat if they didn't (and some have not).

On the subject, a little light pinging apparently is not bad for a vehicle, and General Motors even claims it is preferable, giving you the "greatest efficiency" for your fuel. Heavy, consistent pinging, especially under acceleration IS a concern.

Of even greater concern would be that, in my experience, these things tend to get worse in time. Indeed, some vehicles that ran just fine on 87 when they were new, ended up having to run on straight premium in the last years before I junked them (yes, I kept them tuned and in good, running order).

This is something to be watched carefully through the years.

Tom Wenndt

Where does GM say that? I think that is just an excuse for poor engine design and management. I've never read any legimate source that said detonation is good for an engine. And most engine makers go to great lengths to prevent it.

I'm not saying it causes instant death as it seldom does, but heavy pinging under a heavy load can trash your pistons in short order.

Matt

I will do one better than that. I am still looking for when Consumer Reports last did a report on gasoline. But whenever that was, even they also said, "Don't worry about some occasional light pinging - DO worry about consistent, heavy pinging, especially under acceleration."

I'm with you. I don't like it even a little bit, and when I hear even a single ping or two (and I know that this is what I am hearing), I go to a higher octane fuel. And as I also mentioned, I would expect the problem only to get worse through time.

Agree with another writer - the problem seemed to be less in the Winter then in the Summer in the vehicles where I had this problem (none recently).

Tom Wenndt

Octane increasing additives are used EXPLICITLY to reduce pinging or premature detonation. That is actually the only value with higher octane fuels since they have lower energy content than low octane fuels.

Higher octane fuel may allow particular engines that need them perform better thus offsetting the lower energy content for those engines.

gerry

True, but what is your point? This has nothing to do with the VALVE train, which was my point.

And there is no such thing is premature detonation. There is preignition and there is detonation, there isn't premature detonation. All detonation is undesirable, no matter when it occurs.

True. Most modern engines have knock sensors to detect detonation. When this is detected the engine control computer will typically retard the timing until the pinging stops. This will reduce the performance of the engine. If higher octane fuel prevents this, then it can increase the performance of such an engine.

But this still has nothing to do with the valve train. :-)

Matt

Seems we just are playing with words here ;) An internal combustion engine detonates it's charge. It is fairly violent compared to igniting a gas burner in a furnace, thus "detonation" is a reasonable word for "ignition" in this context.Whichever word you prefer, I believe we can agree "initiation of combustion" and it's timing, speed of progression and cause is what matters.

If the valves "chatter" with lower octane fuel as indicated in the original post but do not with higher octane fuel, it has something to do with the charge igniting before it should or the flame (blast) front traveling too fast. Delay in ignition or speed of the flame front is the only thing higher octane fuel changes.

gerry

No, an internal combustion engine ignites its charge and burns it. Yes, it burns very fast, but it is a burn, not an explosion, which is what detonation is. Detonation and combustion aren't the same thing with respect to an IC engine.

My point is that either the valves weren't chattering and the OP was hearing detonation, or the valves are making noise and something is wrong other than octane. The two simply aren't related. The valves are closed against their seats when the combustion (or detonation) occurs.

Matt

Here is a nice tutorial on the subject:

Matt

Look up " detonate" in a good dictionary and you will find it is not as defined as used in the above reference! It is not "spontaneous combustion"!

An example is

"involves a shock wave and a reaction zone behind it"

Indeed one detonates a thermo nuclear weapon and that sure is not spontaneous combustion as defined in the reference you choose ;)

This is just to point out that different groups use different jargon. Thus I indicated not to worry too much about folks using different wording. I concede I use the words in more general engineering context, not automotive jargon.

In context of this discussion and using your choice of wording, octane affects both "pre-ignition" and "detonation", inhibiting both.

gerry

Read the reference you posted

"can actually cause fracture of valves-intake or exhaust"

The resonance can cause the valves to unseat briefly and force them closed with force.

gerry

Detonation used in the automotive sense isn't all that different. The spontaneous combustion is in effect an explosion. That is what makes all of the noise. It is the shock wave hitting the cylinder walls, piston and head that makes the racket.

It makes sense to use automotive jargon when talking about an internal combustion engine, which was the topic at hand.

Octane inhibits detonation, but has almost no affect on pre-ignition. Pre-ignition typically occurs from hot spots in the combustion chamber. Octane slows down the burn rate and lessens the chance of spontaneous combustion, but it doesn't prevent hot spots and it doesn't prevent ignition so it has littly if any affect on pre-ignition.

Matt

I saw the above statement.

I don't find this statement in the article, even using the search function. Where do you find this?

Matt

The article states resonance and the structure of the engine to vibrating. There is no reason to presume a valve held closed only by spring action stays firmly seated and unaffected by the engine structure vibration.

Something that "can actually cause fracture of valves-intake or exhaust" surely implies severe stress on the valve train. Even if the valves stay closed, a stress severe enough to deform them will be transmitted to the cam assembly which is in positive contact (via hydraulic action).

There may well be a jargon issue as to this being "valve chatter" but the reference clearly states valve involvement.

The below is on page two

" Detonation

Unburned end gas, under increasing pressure and heat (from the normal progressive burning process and hot combustion chamber metals) spontaneously combusts, ignited solely by the intense heat and pressure. The remaining fuel in the end gas simply lacks sufficient octane rating to withstand this combination of heat and pressure.

Detonation causes a very high, very sharp pressure spike in the combustion chamber but it is of a very short duration. If you look at a pressure trace of the combustion chamber process, you would see the normal burn as a normal pressure rise, then all of a sudden you would see a very sharp spike when the detonation occurred. That spike always occurs after the spark plug fires. The sharp spike in pressure creates a force in the combustion chamber. It causes the structure of the engine to ring, or resonate, much as if it were hit by a hammer. Resonance, which is characteristic of combustion detonation, occurs at about 6400 Hertz. So the pinging you hear is actually the structure of the engine reacting to the pressure spikes. This noise of detonation is commonly called spark knock. This noise changes only slightly between iron and aluminum. This noise or vibration is what a knock sensor picks up. The knock sensors are tuned to 6400 hertz and they will pick up that spark knock. Incidentally, the knocking or pinging sound is not the result of "two flame fronts meeting" as is often stated. Although this clash does generate a spike the noise you sense comes from the vibration of the engine structure reacting to the pressure spike. "

... "can actually cause fracture of valves-intake or exhaust"

gerry

OK, so you made up the above statement. I just wanted to confirm that.

Matt

I appears so. It's hard to see how a pressure spike in a sealed combustion chamber could cause the valves to open, since they'd be under extremely high pressure holding them closed.