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.

[lagos]

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 safc does NOT interrupt the signal from the ecu to the injector. in fact, it does NOT directly control the fuel injectors in any way. what it does, is try to fool the ecu into seeing less/more air then there actually is.

the stock ecu has a fuel map based on the amount of load that is put on the engine. load is determined by signal from the map sensor and your throttle position sensor. the load map is an a 0-100% basis.. now say you take an safc and take out 50% air. this will put the ecu at about 50% load, while your boosting the crap out of the motor. you can imagine that the stock ecu probably has a lot more timing advance at 50% then it would at 100%, so that the stock motor has good mid range response, and less timing at 100% to keep things safer, under such harsh conditions.

thats why piggy backs like the safc are not the right way to tune for bigger injectors, and a car thats making 2x the factory HP/tq.

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.

by installing a 2bar map, you are just taking the stock fuel/timing maps, and stretching them out. so now 100% load = 14.7psi and not 0psi. this just helps you get around fuel cut, and gives you some room for adjustment on the stock ecu fuel maps.

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?

while removing air with the safc does cause timing advance by putting you in a different load point, its important to remember, that even if you dont make any negative corrections with the safc, your timing maps are still pretty advanced because the motor started out as NA. the general rule is, that the more boost you want to run, the less timing you want, to keep things safe.


the btm is a very crude device, thats mostly used by domestic guys with a supercharger. i wouldnt waste my money on it. you should get something like an emange or a stand alone to do it right. instead of spending 200 on the btm, buy yourself a water injection kit. it will do more good then the btm will.

This post has been edited by lagos: Sep 5, 2007 - 12:39 PM

[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?

[lagos]

the safegaurd is an awesome product, but you would be better off putting that money, and the money spent on an safc, into buying a stand alone.

[WALKER]

the safegaurd is an awesome product, but you would be better off putting that money, and the money spent on an safc, into buying a stand alone.

The reason I ask is because I already have an SAFC2 and there is someone locally that is selling J&S safeguard system for $200.

I don't really know a lot about the J&S system since I never looked into as an option, how exactly does it work? It says on their site "With the J&S SafeGuard installed, every cylinder is monitored over 125 times per second and the ignition timing adjusted accordingly."

Is it a standalone system that will work with the stock injection system though, or does it still need an aftermarket ignition system?

This post has been edited by WALKER: Sep 6, 2007 - 2:45 PM

[lagos]

a stand alone should work with all your stock igniton.

if you can score a JS for 200...then do it (actually, i dont know what they go for new). its kind of like a super knock sensor. it will give you very good knock protection.... but you have to remember that its not a tuning device. just a better way to save the motor, once knock happens.