saitotiktmdog

Unless the engine can sense the octane or maybe ping and retard the ignition timing I dont know how the engine would compensate for this.

MudHippy

Can you say Knock Sensor?

http://en.wikipedia.org/wiki/Engine_knocking

aa1911

iTrader: (1)

I have done the math countless times in all my vehicles; bottom line, 92 (or 93 whatever you have in your area) octane gets me more mileage and when I do the math, the extra cost of the premium ALWAYS pays for itself and then some in increased mileage. plus you're running better fuel thru your engine. When gas was $.87/gallon, a 20 cent increase for premium was a lot; nowadays with $3 plus/gal, 20 cents is crap. HIGH OCTANE!!!!

saitotiktmdog

Oh duh. But it still would not be able to automatically advance timing to take advantage of premium. Knock sensores only trigger timing retard.

sb5walker

Knock sensors only trigger a pulse of current. When designing EFI control for a new vehicle, the computer can be programmed to respond to that signal however the programmers want it to.

saitotiktmdog

They sense noise on an engine basically. When I mounted mine on my 22re that came with my sds system they specify where to locate it so that you do not pick up valve train disturbance and have your knock sensor always sensing noise and therefor always retarding the timing and not too low or it would not properly sense knock. Yes it creates an electronic pulse but that only comes from when the motor is knocking or pinging dut to the premature ingnition wave impacting the piston on the up stroke. If there is no knock sense it will use the normally programed ignition timing values. It will not sense a lack of knock and advance the timing. If you engine does not knock with regular gas than it wont knock with premium gas. The cars ignition timing curve is based on what fuel is recommnded in the car. Therefor there will be little to no gain from premium fuel. Yes with a knock sensor you could run poor grade fuel in a car that specified premium but it would retard the timing and cause a loss of power, spike in egt and potentially cause other problems as well.

sb5walker

The knock sensor is a stupid electrical device that produces a ping of current when there is a noise of the right frequency (tuned to the frequency of a detonation). It is not "smart": it doesn't have any idea what "timing" is or what it's connected to or any idea whatsoever of where it fits into the big picture. It's a dumb device that creates a pulse when it detects a ping.

A computer which has a circuit attached to a knock sensor will therefore "know" when there is pinging. And programmers can do anything they want with that information when they are designing and programming the computer. So it would be very easy to program it to go through a tuning phase after the motor reaches operating temp to try advancing the ignition timing until it picks up pinging, and then back it off a little. This would be no trouble from a programming standpoint. I know, I've been programming computers for a living since 1985.

And it sounds like the Lexus 400 that tried4x2signN referred to may be doing something like that.

saitotiktmdog

That is basically the same thing I said. All the sensor does is sense noise in the engine and the computer does the rest. You are right if it is programmed into the ecu to advance timing untill ping is detected in kind of a learning initial phase that could work, but I would assume that these timing advance values would be built into the program, Is that correct? Kind of an, If else program. If no ping move to timing curve b else stay at timing curve a. Or can the computer automatically generate a timing curve on its own without user input. For my sds I have to do it all myself. I can only programm in what maximum advance will be, given no boost or ping and then as boost is detected and or ping it takes timing away.

sb5walker

Yeah, I really don't know if there is enough difference between the behaviors of different octanes of fuel to require a different advance curve for the 90 than 87 octane, for example. If it did make a difference, it probably wouldn't be too difficult for the computer to guess what kind of fuel there is and to choose the appropriate curve.

I do know that differing amounts of ethanol DO make a big difference, and it would be very helpful for the computer to know how much of that garbage there is in the fuel, but I don't know how the programmers might attempt to determine that. Probably they would have to make some middle road compromises, which I think ECUs do anyway.

It would be interesting to talk with one of the geeks who program these things and find out for sure.

saitotiktmdog

Yeah that would be interesting.

MudHippy

Right and wrong, then right. Older ECUs couldn't automatically advance ignition timing, correct. Newer systems can, your incorrect in that assumption. You are correct however that knock sensors sense knock with their purpose being to transmit that detection to the ECU which uses the information to retard timing. Duh.(pardon the pun)

Ever wonder why you can no longer set/adjust base ignition timing manually on engines these days, as in OBD-II vehicles? Because the computer DOES fully control ignition timing. And it DOES have the ability to advance the ignition timing untill knock is detected and when it is detected to retard timing accordingly. So, because higher octane fuel is more knock resistant, it can advance the ignition timing more so than with lower octane fuel. Avdancing the ignition timing yields better performance on all grades of fuel, including 87 octane too. Staying "on the edge of detonation" is always going to improve an engine's performance regardless of what fuel it's using. Sorry, but these things are TRUTHS.

You now longer have to make manual adjustments to the distributor or adjust the octane selector(there are such things on some vehicles), to compensate for octane grades higher than 87, as is the case on OBD-I/pre-OBD vehicles. 87 octane is just the lowest standard grade that manufacturers used to establish safe base timing, which will always been as retarded as possible. 87 octane fuel is NOT the only grade that the engine can run on, it's just the LOWEST octane grade that the engine is designed to run on. You can tune the engine to run better on higher grades even with the older systems. Newer sytems(OBD-II)have eliminated that need to do so. Simple as that.

Advancing ignition timing to run on higher grades than 87 is NOT a new concept. It has been done for decades and will be done for decades more into the future. You just don't have to get under the hood to do so on most vehicles anymore.
Keyword: mechanisms(plural) two of which are stated clearly there.

1 to detect knocking and 1 to adjust timing.
So the quoted statement above is completely accurate. Sorry to burst your bubble.

Trust me, it doesn't take a geek to understand that there is DEFINITELY going to be a difference in how much performance and/or ignition timing advance one can achieve based on the octane grade of the fuel used. Even 87 vs. 88 octane. Once base timing is established though, the timing curve is going to be very similar between any fuel really. So, it's more about setting/establishing the base timing and less about modifying the timing curve. To think in terms of maximum advance as being relevant is more confusing for sure. Base timing is the opposite, meaning it's the minimum advance. Maximium advance is already going to be set far enough advanced for optimal performance at high rpms regardless of octane grade of the fuel used, in most cases. And unless you're looking to squeeze every last bit of power out of the engine at, near, or above redline rpm, it's of very little value to concern yourself with.

In laymans terms tuning an engine designed to run on gas to run on alcohol or any mixture of the two will need to address two primary aspects. The amount of fuel to be injected. And advancing the timing to make use of the alcohols higher octane properties. Alcohol is "thinner"/less dense than than gas, so more of it needs to be injected to result in equal engine performance compared to gas. That yields lower mpg with alcohol as fuel. The advanced ignition timing issue is much easier to deal with though, and/or is effectively controlled by the engine's computer within it's given parameters. More power can be made running on alcohol, or higher concentrations of it in pump gas(i.e. E85), because it's much higher in octane(E85 is rated ~95+ octane).

sb5walker

Yeah, I wasn't questioning that the computer would need to advance the ignition more with high octane - obviously it would. I was responding to the idea of a different advance curve - the amount that advance would vary at the different rpms. I do think it's possible that different fuels might have different behaviors that would allow a lot more advance relative to other fuels at one end of the rpm range than the other. Perhaps high octane could not take much more advance than low octane at low rpm, while needing a lot more advance than low octane at higher rpms, thus requiring the computer to advance ignition on two different curves.

As far as alcohol having more power, I'd bet that you would need to have a lot more compression to get more power out of E85 than gasoline, since the alcohol only has about half to two thirds as much energy per volume as gas.

aa1911

iTrader: (1)

has anyone experienced major differences between different gas stations? about 3 out of 4 fill ups at Shell stations, I get better mileage than most any other place.

MudHippy

The timing curve isn't user adjustable by means other than reprogramming or rechipping the ECU(or adding an additional ECU)on EFI engines. Though the stock ECU, even the older systems, will still have some ability to change the curve to compensate for higher octane fuels. Again, it's going to use the knock sensor signal to detect knock at all rpms. Where it finds knock, regardless of rpm, it will retard the timing to eliminate it. You've just got to give these things more credit for the ingenuity of there design. It's really not as complicated as one can imagine it to be. The computer can handle the timing curve once initial/base timing is set manually or is established by the ECU. Due mostly to the minimal need for corrections to the timing curve between different fuel types/octane grades(as in all the different kinds of "pump gas"). Reiterated, it's more important to get the base/initial timing set and let the ECU do its job from there. If you even need to do that much, which you don't on OBD-II systems as they do it all for you.

That having been said, one of the main reasons to upgrade the ECU by means of rechipping/reprogramming or adding a stand-alone/piggy-back unit is to alter the timing curve. That's not all they're good for as they can also adjust for longer or shorter injection durations too. But, even then there's only so much that those things can do for the engine's performance over the stock ECU programming. Especially so for a stock engine without other fueling enhancements or "power adders" like hi-flow heads/P&P intake manifold/exhaust headers/larger valves, turbo/supercharger, larger injectors, raised compression ratio, or the use of oxygenated fuels(i.e. nitrous injection, propane injection, nitromethane, etc.)or anti-detonants(i.e. methanol injection). Then it becomes much more important to more accurately control ignition timing, in all aspects, to get the most benefit from those enhancements and prevent engine damage.

Back to the alcohol subject. It isn't required that the engine's compression ratio be altered to run on alcohol to gain the benefits of it's higher octane rating. Running alcohol allows for higher compression ratios than can be achieved for gasoline without detonation. However, you can still get some of the benfits of its higher octane rating from running it in just about any engine designed to run on gasoline. The following will describe what I'm getting at in fuller detail.

Keywords: potential efficiency that it is possible to gain with this fuel

Meaning, you'll get more power out of it in an engine specifically designed to run on it. That engine will necessarily be one with a relatively higher compression ratio however. You were headed down the right track there, but strayed into the fuel economy arena(energy per volume). Instead of thinking in terms of fuel efficiency or power gains to be had(use of that volume for power). Remember, dollars per mile(economy), miles per gallon(efficiency).(And also keep in mind, higher mpg = higher HP, they're always directly proportianal to each other.) BUT, if pure alcohol fuels(methanol/ethanol)or E85 can be bought cheap enough, their inherently lower heating values(units of energy per unit mass/volume)can be offset in relation to gasoline with regards to fuel economy. Therefor their economical value can be increased to the point that they're just as economical as, or more economical than, any octane grade of "pump gasoline". So their fuel economy properties really just depend on how much you pay for them. Though E85, or E100(pure ethanol), will always be able to outperform the other types of "pump gasoline" in the fuel efficiency department.

I plan on installing a MegaSquirt stand-alone unit in the near future to optimize my 3VZ-E's performance on many different fuels. Which can easily adjust the timing curve and injection duration in a cost-effective manner with virtually any fueling setup.

saitotiktmdog

I have an sds system and can program my ignition timing values for each rpm value. With a distributor engine you can change the base timing but the advance is either mechanical or controlled by ecu. Which means it has a max value of advance, so you can really only adjust the base timing based on what you wan your max timing to be. Some msd systems are this way also. The only real way to get a fully customisable ignition is to convert to distributorless ignition. To some extent OBDII cars do have a learning ecu but I do not know the extent of what it can learn on its own. It probably consists of if else statments or for loops, using c++ notation anyways.

MudHippy

Good points. I have no experience as of yet to speak more on the "how to" matters of software programming for fuel efficiency. I can add that any stock EFI system will use the ECU, as opposed to mechanical advance, to adjust the timing curve above the set base(user set or not). And that older systems only allow for the setting of base timing by the user, by means of manually adjusting/advancing the distributor. I'm not sure what you're meaning by "max value of advance" however. If you mean that the base timing can somehow effect the maximum timing advance achieved at high rpms, I believe you're mistaken. The timing curve after/above idle rpm is totally controlled by the software of the computer on all stock EFI systems. Base or intial timing is just that, it's the base or initial starting point from which the timing curve originates, as in it's the ignition timing advance when at idle rpm. It has nothing to do with where the curve ends up though, as in the maximum advanced point BTDC that the ignition timing is allowed to be set at high rpms. That set point is entirely up to the ECU and whatever timing map it's programmed to use to determine what the maximum ignition timing advance allowable should be at high rpms. Mechanical advance is antiquated technology and hasn't been used by manufacturers for many decades. So I won't elaborate on how maximum timing advance is controlled by those systems.

This is how I understand what's called total timing advance for systems with mechanical spark distributors as are found on most vehicles, with EFI or not. Whether or not that equates to what you've called "max value of advance" I'm unsure. So let me elaborate on total timing advance.

Mechanical ignition systems use a mechanical spark distributor to distribute a high voltage current to the correct spark plug at the correct time. In order to set an initial timing advance or timing retard for an engine, the engine is allowed to idle and the distributor is adjusted to achieve the best ignition timing for the engine at idle speed. This process is called "setting the base advance". There are three methods of increasing timing advance past the base advance. The advances achieved by these methods are added to the base advance number in order to achieve a total timing advance number. Those methods are mechanical timing advance, vacuum timing advance, and computer-controlled timing advance.

For the sake of simplicity I'll describe the type most commonly found on modern engines. Computer-controlled timing advance.

Newer engines typically use computerized ignition systems. The computer has a timing map (lookup table) with spark advance values for all combinations of engine speed and engine load. The computer will send a signal to the ignition at the indicated time in the timing map in order to fire the spark plug. Most computers from original equipment manufactures (OEM) cannot be modified so changing the timing advance curve is not possible by the user. Overall timing changes are still possible, depending on the engine design. Aftermarket engine control units allow the tuner to make changes to the timing map. This allows the timing to be advanced or retarded based on various engine applications.

Here's an example of a timing map.

I also have very minimal experience with OBD-II vehicles. I've only ever owned one, and still do. It's a 98 Monte Carlo. I have no hard evidence to show that it can achieve better fuel efficiency on octane grades higher than 87. But, if you're willing to take my word for it, I have definitely noticed that to be the case based on experimentation. I get more power and more mpg when I put premium gas in the tank. Which leads me to believe that the ECU has made adjustments to the timing curve to achieve those results. Because I sure haven't. The ignition timing is not user adjustable on it, in any way/shape/form in stock configuration. Furthermore I've made no attempts to add, or substitute, any aftermarket components to it. It's "bone stock" still because I'm more than pleased with it's performance as such. That's WAY more than can be said of my 88 3VZ-E. I've found that Toyota had, without any doubt, "de-tuned" that engine quite a bit for whatever reason. It's twice the performer it was before I started tuning it. Well maybe not "twice", but it's getting there.