Shadowfax,
Prove it yourself. What damage? Please over stressing the pistons? What liberal arts degree did you fail to get. It was not engineering or metals or even engine design. Modern cars largely do not have pre detonation due to knock sensors BTW. Almost all engines actually start ignition before TDC, So I know you are not very knowledgeable on this point. The stress coming up is similar to the stress going down within about 25% and the materials are well built enough to do this every day for 100k and more miles. In the past like the 70S hemi engines not so much but even they suffered only a slightly shorter life due to bad tolerances when built at the factory.
If the octane is to low your engine will “ping” and “knock”…You can detect these things…Many if not most cars labeled “premium” will run fine on regular…If you can detect knock or ping under acceleration, then your car is telling you to use premium…,
Some cars with higher compression ratio need the octane higher to burn correctly at the higher pressure.
Burn correctly? Higher octane does NOTHING to “correct” the way the fuel burns. Higher octane means the fuel is more resistant to igniting from the heat of compression, nothing more.
Otherwise pinging results.
The lone correct statement in this quote.
Pinging is a poor detonation condition.
No, it is not. Pinging is the result of the very violent collision of more than one flame front within the combustion chamber. Once the fuel combusts the chamber pressure increases rapidly. That’s the whole point of burning the fuel. But if the fuel is burned too early or too quickly the pressure will rise so rapidly that unburned fuel in other parts of the combustion chamber will ignite from the increased heat. That creates multiple flame fronts.
Normally this will not hurt the engine but it does hurt mileage and power.
All it takes is a quick look at a piston that has suffered a lot of pinging to prove this wrong. It looks like it’s been hit with a ball peen hammer. The most typical problems resulting from pinging are broken piston rings and the occasional piston with a hole in it. Most people consider this “hurting the engine”
Modern computers will try to minimize the issue but a a poor performance curve.
Modern computers minimize the issue to prevent destroying the motor.
There is no clear damage to the engine from pinging aside from performance. This is a big myth and a lot of folk here drink that koolaid. But it is just unscientific.
I’d like to see some “scientific” evidence backing this up. This is a condition known as long as there have been internal combustion engines. My statements come from a Buick factory maintenance manual. Where did yours come from?
While engine damage due to pinging is not very common…it COULD happen. But it would have to be prolonged pinging…not just some occasional pinging every once in a while.
http://www.peugeotlogic.com/info/info1.htm
The 70’s hemi engines didn’t have Alloy or Aluminum pistons.
. You make an inane statement claiming that pressing down on a piston that is being forced upward places no more stress than pressing down on a piston that is already going down, a statement that goes against not only physics, but common sense, and then expect me to run around digging up proof that you’re wrong. The burden of proof is on you, because you’re the one making the foolish claims.
Well I disagree due to the fact that being pushed down on (slightly) happens all the time during compression. The flame front in a normal ping (not caused by grossly bad timing, which the computer wont allow anyway) initiates before tdc in all motors of this modern age. They are built to run just at the critical edge of ping. Many ping but it is not the old school head blasting, turn up the radio ping. The reason is that at flame front start it takes microseconds for propagation and max pressure. You want max pressure of combustion to occur just after tdc. Since this takes time you detonate the fuel before TDC. It is simple chemistry. Things are not IMMEDIATE. That is what timing does. Does this clarify enough for you to understand?
I disagree with the previously mentioned premise that pinging is not harmful to an engine and that is based on teardowns of engines that suffered because of it; including one car I bought “as is” with a known rattle and which turned out to be disentegrating pistons due to pinging.
Disable the EGR system on many vehicles and see what happens then.
Pistons in modern engines are designed to be light weight as this helps make the motor more efficient, less moving mass to stop and reverse direction. Light weight means lighter metals, thinner metals, and different shapes. Perhaps modern pistons aren’t so robust as pistons of olden days. I remember hearing knocking that sounded like marbles bouncing around inside someone’s motor. Mostly the cars of the 50’s, 60’s and '70’s tolerated some pretty heavy knocking before burning a hole in a piston.
Fancier cars with high tech engines (BMW for instance) if the engineers designing the motor say to use premium I think you are nuts to question it. Whether you can hear knocking or not and does it do damage or not isn’t the point. One car can tolerate knocking and another can’t. If your car calls for premium and you use regular, you are simply taking a gamble. Maybe you win and save a few bucks at the gas pump. But maybe you lose and spend a whole bunch of bucks (as in a couple of thousand) on a major motor repair.
I remember knocking as rod knocking. IE the wrist bearing on some cars would just be sloppy. This caused much piston damage. A knock is really not heard much anymore as this sets the engine light in a jiffy.
The effect of a ping is transitory and is in terms of force not largely greater than the force of normal ignition even given the increase of pressure on the bearings. They are built to withstand those forces for 150,000 miles or more. I always used 87octane in my vw bus. It was always underpowered and pinged merrily up every hill for 90,000 miles till it was too much rust to play with any more. It had more than 200k at the end I just did not drive all of them. One engine replacement for 600$ when I got the car and I was good for 90k of uphill music.
Yes.
For those interested in a coherent explanation of the terms being thrown around this article should help.
IMO depending on the knock sensor to compensate for lower octane is not a good idea. Detonation has to occur before the ECU compensates. The engine was not performing properly when the knock occurred and won’t be for a time after due to the compensation. Knock sensing will save your engine but it won’t do anything for performance or economy.
Peak combustion pressure at TDC is not desirable. At TDC (assuming no wristpin offset) pressure on the piston does no useful work against the crankshaft. Peak pressure should occur ATDC at a time determined by the pressure profile and the crankshaft / connection rod geometry.
Don’t confuse piston slap for loose wristpin bearings or ping.
So I turned in my car for one with a smaller payment.... We have established that I am cheap.I don't know about that. You've traded in a car that isn't paid for with the sole goal of lowering your monthly payment, which usually isn't a financially sound decision. Yes, your payments are lower, but don't you owe more now? If so, this looks all around like a decision that is penny wise and pound foolish.
@euryale1, you’re comparing an air-cooled VW Bus to a modern liquid-cooled engine that appears to require high octane fuel. Do you not see the difference?
Well, it seems that I need to visit my own question more often. Thanks a lot to everybody who has taken time to offer an opinion (and occasional dig). Nice to know people care.
So in answer to a couple things, it’s an Acura TL, 2006.
Because it’s used it’s actually less out of pocket than my previous car grand total. So I AM saving some money there.
As for if the handbook says “require” or “recommend” I’m not sure. I do know that it mentions something about “if you put 89 or less in knocking will result” and "91 octane or higher."
And for those who asked, the Sunoco near me offers the following octane: 89, 93, 96. I swear.
More more! Love that something stupid I posted caused so much interest!
Of course I didn’t do the math, and it probably is only a couple bucks each fill up isn’t it… oh well… I’m going to pretend that I’m still on the fence and let y’all fight it out more!
Thanks!
I have an 07 TL, which with the exception of the transmission, GPS software, and a few cosmetic changes is the same car as yours. Premium fuel is required in our engines. Some TL’s actually ping slightly even on 91. I’m guessing you live at or near sea level to have those kinds of octanes offered. You want the 96, if so. Otherwise, 93 would be fine, though you will get better power and mileage on the 96 since the knock sensor won’t have to retard your timing as much.
Just found this, and here’s what Tom and Ray have to say about it…
About 1/4 way down the page…
"Use the grade of gas you need and nothing higher.
Does your owner’s manual say “Premium Unleaded Only”? No? Then don’t ever use premium fuel. There. We just saved you 40 cents a gallon… or $8 on a 20-gallon fill up. If your engine is designed to run on regular gas, there’s absolutely no benefit to putting in “high test.” It pollutes more, it costs more, and doesn’t give you any benefit in performance or fuel system cleanliness.
Now, what if your car DOES call for minimum 91 octane? Well, next time you buy a car, dummkopf, check what kind of fuel it requires first. We’ve always said that once you buy the car, you’re stuck. You’ve got to use 91, because your high compression engine will ping if you don’t. Now most cars have “knock sensors,” that retard the timing via the engine management computer (effectively lowering the compression) to protect the engine, in the event that you happen to get some bad gas, or have an emergency and can only get regular grade fuel. So we got to thinking, what would be wrong with using the knock sensor all the time? What if you put regular gas in the car all the time and let the knock sensor do its job and retard the timing? You’d have a little less power, but that extra $8 bucks a fill up might be more important to you than power right now. It would be to us.
It’s a controversial theory, we admit it. But that’s never bothered us before. And we can’t think of any long-term effects of driving with the knock sensor retarding the timing. So our position (for the time being) is… use regular. Who cares? Now, if there are any actual automotive engineers in the audience who have worked on knock sensors, who want to tell us why we have our heads up our keisters, feel free to write to us. And if we’re convinced that we’re wrong, we’ll happily change our recommendation."
That’s one of the areas where The Guys and The Rest Of Us disagree. Knock sensors can only retard the timing so much. If they retard the timing as much as they can and you’re still pinging, there’s nothing more they can do.
I’d ask, if Tom and Ray are right about this, why do the automotive engineers who designed the engines specify premium fuel “only?” It’s no skin off their nose if you don’t buy the (slightly more) expensive gas. They aren’t getting kickbacks from gas companies. Is the position of Tom and Ray that automotive engineers are not smart enough to understand the requirements of the engine that they designed?
Myself, if someone designs a piece of machinery and then turns it over to me, I’m going to tend to listen when they say “You’re going to damage it if you don’t do this.”
Eury, the term “knocking” simply refers to the sound and is loosely used to describe both ignition caused by compression generated heat before the spark plug fires and often rapping sounds from other sources as well. The only way to really tell what’s happening is to look at the engine. Could be wrist pins, couuld be crankshaft bearings, and knocking could even be a broken valvetrain part.
Knocking can be very serious, because if it is caused by preignition that means the shock from it is not only felt by the piston but is traveling down through the wristpins, the connecting rods, and the crank as well. The inertia in the flywheel combined with the inertia of the car, combined with the other cylinders firing and turning the crankshaft, all combine to creat a lot of force on the crank as well as in an upcoming piston. An early explsion trying to suddenly spin the crank in the opposite direction abd to blow the piston back down can overstress numerous components.
Continuous operation with pinking or knocking can be very destructive. If you’ve been pinging merrily up every hill for 90,000 miles, than you truely have a guardiian angel.
“You’ll drop 40 grand on a car, and whine about $1.20 a week extra to fuel it?”
I don’t have $40,000 for a car. Can I whine about that instead?
It all depends on where you live and what kind of driving your doing… If your living in relatively flat lands and just commute, then use the cheapest gas you can get. However, if you live in hill country, or you are hauling a lot of poeple and things all the time, then you will need to use the higer Octane as reccomended. I had a truck that required the HIGH Octane fuel, the only time I bought that was when we took vacations where we would be driving long distances, towing something, plus all of us, luggage, and the dogs. However, for the day to day driving, I just used the cheap stuff. We got 325,000 miles out of a 1987 F-150 doing that… I don’t see a problem. The more modern cars now have computer systems that compinsate for whatever you put in the tank. Unless you have a special marketed engine, you will be good on the cheap stuff.