[E4ODnut]

I'm not sure that I understand why it is preferable to have all the fuel delivered before the intake valve starts to open, unless it is detrimental to be spraying the air fuel mix on an open valve. I would think that at idle and at low engine speeds and loads spraying on an open intake valve would be preferable. I do understand that as the speed and load increases there is not enough time for the injectors to deliver the required amount of fuel, so some will have to be sprayed on the closed valve to get pulled into the cylinder on the next intake stroke.
Consider a garden variety street engine with each cylinder injector firing once per revolution. Wouldn't the best compromise be to have the the injector pulse finish about twenty degrees or so before the intake valve is completely closed? Half the fuel will still be injected on the closed valve before it starts to open. The other half, depending on speed and load, will be guaranteed to have at least some of the charge delivered on an open valve. Is there a flaw in my logic?

[PSIG]

I'm not sure that I understand why it is preferable to have all the fuel delivered before the intake valve starts to open…
Is there a flaw in my logic?

IMO, at this point, the technical response is less important than the premise of the question, or we could go in circles forever. Your logic appears sound, but is based on assumptions. It is therefore a fallacy, if offered as a factual argument. This is addressed in science as a fallacy, in order to prevent presumptions and assumptions to be passed as fact because it "sounds logical".

If we do not know the facts or principles involved, we cannot argue the merit of one position or another. Conversely, we can offer a position based on empirical evidence such as engines using a certain mode, and some findings about it. Or better yet, evidence we have gathered under specific and repeatable conditions, e.g., test results of injecting fuel at various points in the engine cycle. We don't (currently) have that either, nor the conditions for the test. As we have the ability to try stuff; I suggest testing for results, regardless of the causes behind it, as the most direct path to best tuning and performances. Use what works best, whatever that is, not limited by what you think it should be.

• The sky is blue because ozone is blue.
• The sky is blue because it reflects the color of water.
• The sky is blue because cold is blue.

The internet is full of this kind of stuff. Assumptions. They all sound logical, and are all incorrect.

From 42 Falacies by Dr. Michael C. LaBossiere, ontologist:

Fallacies and Arguments
In order to understand what a fallacy is, one must understand what an argument is. Very briefly an argument consists of one or more premises and one conclusion. A premise is a statement (a sentence that is either true or false) that is offered in support
of the claim being made, which is the conclusion (which is also a sentence that is either true or false).

There are two main types of arguments: deductive and inductive. A deductive argument is an argument such that the premises provide (or appear to provide) complete support for the conclusion. An inductive argument is an argument such that the premises provide (or appear to provide) some degree of support (but less than complete support) for the conclusion. If the premises actually provide the required degree of support for the conclusion, then the argument is a good one. A good deductive argument is known as a valid argument and is such that if all its premises are true, then its conclusion must be true. If all the argument is valid and actually has all true premises, then it is known as a sound argument. If it is invalid or has one or more false premises, it will be unsound. A good inductive argument is known as a strong (or “cogent”) inductive argument. It is such that if the premises are true, the conclusion is likely to be true.

A fallacy is, very generally, an error in reasoning. This differs from a factual error, which is simply being wrong about the facts. To be more specific, a fallacy is an “argument” in which the premises given for the conclusion do not provide the needed degree of support. A deductive fallacy is a deductive argument that is invalid (it is such that it could have all true premises and still have a false conclusion). An inductive fallacy is less formal than a deductive fallacy. They are simply “arguments” which appear to be inductive arguments, but the premises do not provided enough support for the conclusion. In such cases, even if the premises were true, the conclusion would not be more likely to be true.

I hope this momentary diversion helps towards reaching better results with EFI.

[E4ODnut]

I don't think I deserved that.

[JHolland]

I'm not sure that I understand why it is preferable to have all the fuel delivered before the intake valve starts to open, unless it is detrimental to be spraying the air fuel mix on an open valve. I would think that at idle and at low engine speeds and loads spraying on an open intake valve would be preferable. I do understand that as the speed and load increases there is not enough time for the injectors to deliver the required amount of fuel, so some will have to be sprayed on the closed valve to get pulled into the cylinder on the next intake stroke.
Consider a garden variety street engine with each cylinder injector firing once per revolution. Wouldn't the best compromise be to have the the injector pulse finish about twenty degrees or so before the intake valve is completely closed? Half the fuel will still be injected on the closed valve before it starts to open. The other half, depending on speed and load, will be guaranteed to have at least some of the charge delivered on an open valve. Is there a flaw in my logic?

Your logic is sound. I think every OEM that I've worked on splits longer injector pulses into two at low RPM so they aren't dumping excessive fuel into the port on a closed valve, so, if you only have one pulse then timing across the valve opening would be a reasonable compromise. Not every application injects on a closed valve either.

[jonbill]

FYI, I've split this discussion of open vs closed valves out to a new topic, because it's a different topic than individual cylinder (ignition) timing.

[jonbill]

so - I think most people's intuition is that fuel should be injected into an open inlet valve.
But, human intuition is very often wrong.
Putting aside direct injection, is there any actual evidence for what is better? and what it's better for?

[JHolland]

There are way too many variables to declare any method better than another, my take:
If you have a race cam you often get fuel stand-off at low rpm and you can see the effect of adjust the injector time, you don't want to be injecting before or during valve overlap.
On an average road engine then ideally you want to inject before the valve opens, just enough for the fuel to evaporate and not enough to start getting wall wetting issues. As you come off idle and throw in more fuel for enrichment its common to split the pulse so the second pulse occurs soon after the first pulse has gone into the cylinder; if my maths is correct then a 1ms pulse at 1000rpm is 60degs so you can have a lot of 'clean' air going in so you usually need to inject early to let it mix in the cylinder.
if you have one pulse like a Speeduino then, if its a short injector pulse I would time the start after the overlap and before the valve opens.
However you time it, on a mild engine you may not see any difference without an exhaust gas analyzer.

[PSIG]

I don't think I deserved that.

I'm sorry you feel that way, and is not a hit on you, but on assumptions. Assumptions, based on guesses, internet lore, or other sources - logical or not - are one of the largest hurdles to tuning. Most have no idea they are assuming anything. My post was not directed to shame or challenge, but to expand horizons and remove limitations. It was intended to be positive, and provide a different perspective that may help many readers in tuning.

As the previous posts also indicate, we again have too many factors to make a rule judgment, even with similar engine types or conditions. We can suggest some observations, principles, factors and contexts to consider; but we cannot suggest a single response as the question begs, nor what may work better with your engine and fuel. So again, my response is to test for what really works best, as it may surprise you. Testing for real-world effects may also answer many of your questions with data, or you can ignore the why and just use what works best, for whatever reasons that is.

Unless your question is entirely theoretical (please say so), the quest is for results. Perhaps a title change to "How to determine best injection angle?" could be more effective?