How do timing, bigger injectors, and boost all go together?, Help clarify some questions. Options

[WALKER]

I have tried searching for some answers to help me out on the whole issue of timing and how it relates to boost and bigger injectors. I unfortunately don't have a good understanding on how the addition of fuel relates to advanced timing. Help clarify what is correct and incorrect about my thoughts and also offer some advice to my questions. Thanks in advance.

Firstly, my understanding of injectors is that it is based on a voltage signal sent to them by the ECU they will open for a certain period of time (pulse width). Therefore if you were to install bigger injectors, for this example say double (440cc vs. 220cc stock), and leaving everything else the same (i.e. stock MAP, fuel pump, no turbo, etc.). This would mean that you would mean that you would be injecting 2 times the fuel because you would be using the stock fuel maps which think they are using 220cc injectors. If this theory is correct this would mean that if you had 440cc injectors and running with no boost you would have to take out 50% fuel to have the correct fuel being injected.

From what I understand is if you are to use a piggyback to control the fuel (i.e. SAFC) it interupts the signal being sent from the ECU to the injector. Now when you remove fuel the ECU advances timing and when you add fuel the ECU retards timing. Why does this occur, does the ECU read pressure that causes the change or does it somehow read the interupted signal being sent to the injectors by the AFC?

The 5SFE is a MAP based car, so therefore it reads the absolute manifold pressure of the intake manifold. This combines with other sensors (IAT - intake air temperature, etc.) to determine the amount of fuel to be injected into the mix. I believe that the 5SFE MAP reads 0-5V, and in the N/A MAP corresponds to vacuum to 14.7psia (0psig). By installing the 2bar MAP from a 3SGTE this changes the range from vacuum to 29.4psia (14.7psig). Now this is required for us to run boost. I believe that it tricks the ECU into thinking there is no boost. What I don't understand is how boost and the new MAP relates to fuel injection or timing, or if it even has any impact on them at all.

Finally, when removing fuel with an AFC, is there a correlation of how much timing is added per quantity of fuel removed? I am wondering if there is an easy way to know how much timing should be retarded in response to the timing added from fuel removed? When I read the MSD BTM 5462 it says that it removes 1-3 degrees of timing per pound of boost, up to 15 degrees.

Now the first question that comes to mind is that at maximum boost would you not be removing the least amount of fuel, therefore you would have minimal timing advance and would not need to retard the timing much at all to get back to normal. However, if you use the BTM you would have the most timing retarded at the higher boost. I guess this would not be bad since you will reduce the risk of detonation, but would you not be retarding your timing overall?

Then on the opposite end when you are off boost and have the most fuel being removed, therefore advancing the timing the most the BTM will actually not be retarding any timing at all? I suppose that this would allow you more power down low since you would be advancing your timing overall and most likely would have a low risk of detonation since your using higher octane fuel.

I know Manny only used the BTM for a very short time because he couldn't get a good tune with it. I would still like to know what amount of timing retard per pound of boost people are using that have the BTM. Once again this goes back to my question of how much timing is advanced per fuel quantity removed and also how does boost pressure get equated into this formula.

[WALKER]

Thanks for answering some of my questions. That really clears things up and makes more sense to me now.

I was just wondering if anyone has tried using a J&S Safeguard system to monitor knock and retard timing on an individual cylinder basis? Would it even work on a 5SFE?