Ok as the title states im a noob to the whoel concept of EFI tuning. i understand the basics of for EEC, but i want to know, how far can it go. And by that i meen how far (hp wise) can a stock ECU take me. i dont see where a harness swap would be nesecary, my logic on this is all wires do the same thing (could be worng).

I know the accel DFI sytem comes with a new harness. As where the AEM system is plug and play. what makes these sytems superior? i know they can be more precision tuned but how valuable is that? will these systems make big HP more reliably by creating safer more and accurate tunes? thanks guys for helping me better understand

 

The factory Ford EEC is nearly impossible to get to run with any injector larger than 83#. The range of valid numbers to input in the eec for things that define what size injector you're running, how much (or little) fuel to squirt while cranking the motor over, etc can only go so far before you either 0 out the number or make it larger than what the EEC can read. For example, if you're running 83# injectors, there is a scalar named Hi Injector Slope and Low Injector Slope. The Hi Injector Slope is typically where you put in your actual size injector, and that's what the EEC uses when you're at WOT (wide open throttle). The Low Injector Slope is used for idle and part throttle, where you don't want the injectors capabilities to be used to the max. So let's say you run 83# injectors. You set your Hi Slope to 83. The Low Slope is usually 20-25% HIGHER, which basically leans those injectors our 20-25% for idle and part throttle. So you try and put in 100 (83 X 1.20, and I just rounded it up). The EEC will take that, now let's try 96# injectors. 96 goes into Hi Slope and you try and put 115 (96 X 1.20) in the Low Slope. Now your car won't start. The EEC's maximum number for an acceptable injector slope is around 112. There are many other example in the EEC where you will hit these kinds of limits.

So having said all of that, the limit of the factory EEC is realistically based around injector size. Somebody can probably get 96's to work, while sacrificing idle/part throttle (i.e. fouling out spark plugs due to it being so rich), but I think realistically it's 83# injectors as I've had first hand experience with running 83's on a factory EEC in a street/strip combination.

83's are at 100% duty cycle at their rated fuel pressure, around 1300 flywheel HP in N/A setup and around 1100 flywheel HP in a boosted setup.

If your combo requires injectors that big, it will be easier to tune the car with a standalone system because:

• a stand alone system can run large injectors (72# and up usually) that are low impedance. The factory EEC can only run high impedance injectors, unless you install a low impedance injector driver (search this forum for more info on that)
• a stand alone system doesn't have the input limitations that a factory eec does (see the example I just described above)
• most stand alone systems are easier to tune in many aftermarket situations because they are based upon speed density and not mass air, hence there's no need for a calibrated mass air meter, or a mass air meter of any kind.
• most stand alone systems have superior datalogging systems than what you can get with the EEC (even if you use a TwEECer, which will datalog the factory EEC). An example of this is closed loop wideband o2. A stand alone system will let you tell it to get your A/F to a certain value, and correct as needed to get it to that value. The factory is is strictly open loop at WOT and does not have the capability to dynamically modify your fuel trims in order to achieve a pre-specified A/F ratio.

There's a lot more to this book than what I've typed. Start with your goals, and work everything else out from there. How fast do you intend to go, what kind of horsepower is it going to take to get there, do you want it to be 100% street, 100% strip, or somewhere in between...etc.

If you're considering a standalone, don't limit your reviews to just DFI and AEM. Look at FAST and BigStuff3 (BS3) as well. You'll find a lot more FAST and BS3 at the track than you will DFI or AEM. That can come into play if you're in a bind for some help.

 

thanks for the input. you pretty much hit every point in why the factory ford ECM couldnt handle high HP demands. worded perectly.

I really like the idea that some are speed density based sytems. i am running a mass air car right now but would like to be able to do away with the meter. ( dont want to convert to a blow through meter) i know speed density factory cars are alot more finiky though. is this the same case with after market ECM's.

You referenced the FAST system. is it a speed density based system or a mass air? and my car will be a 90% street car. it will see the track about 4-5 times a year. and as for HP estimates im going to say as much as i can get and the car still be reliable. do you have any recomendations on what kind of power is no longer reliable. i know anything over 600 isnt usable on the street but there is a big difference in usable and reliable.

I was leaning towards the AEM computer because it utilizes the factory harness. but i dont see where it would be that much of a pain to lay in a new harness. and i have heard its real user friendly. Im also glad you told me about the 83# max on the stock ECM. I was looking at some siemens/rochester 96#'s.

i doubt i will ever see 1000HP and i know it is going to take alot to ever get there, but it is a dream of mine and one day i would like to hit it. I dont necesarily want to ride around on 1000hp but here is what io was thinking, get a good safe tune to drive everyday and make just one temporary aggresive tune then roll 1000hp erase that tune and go back to safe just to say i have a 1000hp car and have the dyno sheet. do you think i would still be better with the 96#'s even if i only have a 700hp car? as you said i could max out the 83#'s but i am not sure what the righ tchoice is on this one. i know im getting greedy by wanting these huge #'s but as stated above its my passion.

thanks for all the help with this. and thanks for the future responses/ help.

 

FAST, BS3, and DFI are all speed density systems. I don't know enough about the AEM to comment.

Based upon my comment above, whatever 83# injectors will handle is pretty much the edge. Realistically, anything over 500rwhp on the street is practically useless. To get more than that, you're talking a lot of expensive supporting equipment (block, rods, crank, pistons, heads, trans, fuel pump/system, etc).

You don't need 96's for 700HP. You can do that with 60# injectors.

 

yea i know on the street 500+ is usless but i still want that 1000hp one day. is there anyway i could detune down to 600 from 1000? my long block and fuel system is up to the challenge, cant say the same for my transmission though.

what are the benifits/ deficits of a speed density system over a mass air system? whick one is better for big numbers?

 

Sure, turn the boost down

For 600-700, I would stick with mass air. Get a TwEECer, a wide band o2, and some conservative tuning.

 

do you think i should reset my goals? just get the whole 1000hp out of my mind?!?! i have no doubt my combo will support 6-700hp. hell i guess i should get that and get used to it first. i think i will. then go for the big power later on. just upgrade everything. well i guess your last post answers my overall question. i DONT need an aftermarket ECU for 6-700.

after a year or so of 6-7oohp i will be back on here asking the magic question that all noobs ask!! thanks for the input, it clarified alot fo rme.

 

So, contrary to what Saleen91 posted... I believe speed density is harder to tune. With Mass air the basic fuel curve means equating airflow to amount of fuel. Speed density means you have to take manifold vacum/boost, RPM, and fuel into account which makes it more difficult to tune (but also more flexible).

So the benifits to mass air = easier tuning, and it'll generally accept more engine mods before re-tuning is required.

Benifits to speed density = No expensive mass air meter, mass air meters are also an intake restriction so they hurt HP a little. Speed density also doesn't care about a vacum leak (which totally screws up a mass air system). A vacum leak usually only results in a high idle. Speed density allows for more tuning flexibility (at the expense of being more complicated to tune).

Some of the newer and more advanced ECU's (like the megasquirt) allow for use of either fueling technology or even a combination of them booth.

To be honest, the best place to start in regards to tuning isn't to pick an ECU but rather to learn how EFI works (what every sensor measures and how that data is used). You need to learn what things like "closed loop EGO control" and "X-tau based acceleration enrichment" means before you'll know which feature you want/need. THEN you can pick an ECU based on their features.... or you can do what most people do and ask "what's best", but you'll never get a completely non-biased opinion because very few people have in-depth experience with them all.

 

i have one of the basics of ford EFI books by charles probst and it is very helpfull. it still isnt near as effective as you guys. i cant ask the book a question if i dont understand. and i really do appreciate the help i have gathered in my short time on this site. i was looking at trents write up on the AEM product and he purchased and installed a map sensor. i thougt these where used on speed density based vehicles.

that is a good comparison between the MAF and SD above. the way i see it if i hae a vacuum leak it needs to be fixed anyways so i guess i am going to stay mass air. i still like the idea of a aftermarket ECM because later on down the road im going to need it anyways. but you are right i DO need to understand all of the functions better. once again thanks for the input guys.