Injector Timing Table questions

[Sendero]

Lately I've been trying to wrap my mind around Ford's injector timing logic. Through EEC Analyzer I have been trying some different calculations at my datalogs and I keep coming up with some drastic changes in my table.

(See my attachment below for the stock LLX3 injector table)

I will get to the results in a second, but first I need to understand something. Injector Firing (leading/trailing) what does this reference? Is it when the injector starts to fire? The way I am understanding it is: Leading fires the injector the calculated PW before the indicated firing time. (Ex. If you have a PW of 5ms and a Injector time event of 375 then the injector fires at 370 and stops at 375) Trailing fires the injector at the indicated firing time. (Ex Indicated time is 375 and it fires at 375 regardless of the calculated PW)

Now for the real meat of my question. If you look at my table below Ford has my injector timing at 352 at lower RPMs/Loads and 380 at higher RPM's/Loads. It seems that the 352 value has to occur while the exhaust valve is still open considering the 380 value during high load. This seems counterintuative to the notion that you want to fire the injector after the exhaust valve is closed and after TDC. Why would you want to fire the injector during overlap? It seems like this would allow the fuel more time to pass through to the exhaust during low RPM operation. It would make more sense for the injectors to fire during the overlap at high RPM operation to get a "jump" on the valve close, but of course this would have more air velocity so you would probably be bleeding more fuel out the exhaust. So that comes back to why the staggered injector firing times. Why not just fire the injector as the exhaust valve closes all the time? (Provided the injectors are sized right and your injectors firing PW doesn't overrun the intake valve close event)

I plugged in all the relevant information into the EEC Analyzer with an older datalog and came up with some interesting results. With Injector Firing Trailing and Exhaust Closed selected it recommended 380 at the lower RPM's and 400 at the upper RPM's. Set it to TDC and it only moves it down maybe 5 points. Set it to Intake Open and it only moves it down 2 more points (total of 7). Why is this so far off of the stock timing? What was Ford's intentions? Its not really surprising that the timing is a lot different because most of my tuning changes have been large deviations from the stock LLX3 settings. These changes have taken me from 265rwhp to 284rwhp so its not like I am hurting the car.

Am I on the wrong path here? Is my logic correct on how this works? I am just trying to understand why Ford has such a large difference in the low RPM timing and high RPM timing. Any help would be greatly appreciated!

[86GT]

Your thoughts are close. The factory uses trailing edge. The trailing edge option is when the injectors must be completely done spraying. The leading edge is where the injectors start spraying. So if the trailing option is selected and the injector timing value is 354° and the PW is 5ms, then the 5ms must be converted to degrees and then subtracted from 354°. once this is done for all load and RPM ranges you will most likley have the same value for all of the injector start degrees. Just keep in mind that the trialing edge is when they must be completley done. So if you take the higher values such as the 400 and subtract the larger PW converted to degrees, you will start at the same place.

Here is the trick, most of the factory cams have very little overlap, and if they do have an overlap it usually occurs after TDC. This means by spraying early will only cause puddling or it could pushing the mixture back up the intake. The only time the the fuel will go out the exhaust is when you have an overlap and it is prior to TDC. Prior to TDC the piston is on its way up which causes the fuel to be pushed out the exhaust.

If you select the trailing edge option and the intake close event, the calculated result will closely match the factory. Dont forget to place the initial timing of 10°.

After talking to some of the engineers at Ford, They tend to spray early because of emissions reasons, and nothing more. He also told me that it is optimal to spray at max lift and before BDC. This is because this is where max flow is.

Hope this helps

[Italian LX]

Originally Posted by Sendero

The way I am understanding it is: Leading fires the injector the calculated PW before the indicated firing time. (Ex. If you have a PW of 5ms and a Injector time event of 375 then the injector fires at 370 and stops at 375) Trailing fires the injector at the indicated firing time. (Ex Indicated time is 375 and it fires at 375 regardless of the calculated PW)

Not answering your question, but I wanted to emphasize a point that Clint already pointed out; the calculated value is in degrees (not time), so your calculations in your above examples are overly simplified and incorrect.

[Sendero]

Originally Posted by Italian LX

Not answering your question, but I wanted to emphasize a point that Clint already pointed out; the calculated value is in degrees (not time), so your calculations in your above examples are overly simplified and incorrect.

To make sure I had the logic correct, I did make it simplfied for readbility purposes. They were mearly to check my thoughts.

Originally Posted by 86GT

Here is the trick, most of the factory cams have very little overlap, and if they do have an overlap it usually occurs after TDC. This means by spraying early will only cause puddling or it could pushing the mixture back up the intake. The only time the the fuel will go out the exhaust is when you have an overlap and it is prior to TDC. Prior to TDC the piston is on its way up which causes the fuel to be pushed out the exhaust.

The cam profile picture that EEC Analyzer displays, what is considered TDC?

Originally Posted by 86GT

If you select the trailing edge option and the intake close event, the calculated result will closely match the factory. Dont forget to place the initial timing of 10°.

Ok, I did that. Now it tells me to set the timing table to 602? What did I do wrong? If the 600 value is correct then I would assume that Ford is spraying the leading edge of the max lift or exhaust close event. (@ 352* and 380*)

(Note: It is possible that my cam specs are wrong. If you remember Clint, I contacted you a while back concerning 96-98 Cobra Cam specs. It seems that no one has them. But a gentlemen at ModularFords has posted his results which has made me believe the little information I have collected is correct. Time will tell on that one.)

Originally Posted by 86GT

After talking to some of the engineers at Ford, They tend to spray early because of emissions reasons, and nothing more. He also told me that it is optimal to spray at max lift and before BDC. This is because this is where max flow is.

I am going to assume that best emissions output happens when fuel is completely burned by the combustion process. So why spray early? It would make sense (according to my theory in the first sentence) that best emissions output equals most power due to the complete burn of the mixture.

If I am reading what you have said correctly then spraying the trailing edge of the intake close event will give me the best power and the best MPG. This is due to the air velocity being the greatest as it approaches BDC on the intake stroke. There again, I am at a loss as to why Ford would spray early and how it effects emissions output. (unless they were taking into account cam chain slop and production differences in the engines)

Just out of curiosity, how do you have your tables set. (In terms of Leading or Trailing and the spray event) Didn't you say it helped your fuel mileage and power?

[86GT]

Originally Posted by Sendero

The cam profile picture that EEC Analyzer displays, what is considered TDC?

Dead center and north is TDC

Originally Posted by Sendero

Ok, I did that. Now it tells me to set the timing table to 602? What did I do wrong? If the 600 value is correct then I would assume that Ford is spraying the leading edge of the max lift or exhaust close event. (@ 352* and 380*)

(Note: It is possible that my cam specs are wrong. If you remember Clint, I contacted you a while back concerning 96-98 Cobra Cam specs. It seems that no one has them. But a gentlemen at ModularFords has posted his results which has made me believe the little information I have collected is correct. Time will tell on that one.)

what 602? oh you are supposed to use trailing and intake open. This will get you close to the factory. I recomend TDC and trailing.

Originally Posted by Sendero

I am going to assume that best emissions output happens when fuel is completely burned by the combustion process. So why spray early? It would make sense (according to my theory in the first sentence) that best emissions output equals most power due to the complete burn of the mixture.

I can not explaine it completley, but I think by spraying early and having it sit on a hot valve will make it atomize (vapor), which in a sense is burnt. It also helps cool the engine.

Originally Posted by Sendero

If I am reading what you have said correctly then spraying the trailing edge of the intake close event will give me the best power and the best MPG. This is due to the air velocity being the greatest as it approaches BDC on the intake stroke. There again, I am at a loss as to why Ford would spray early and how it effects emissions output. (unless they were taking into account cam chain slop and production differences in the engines)

Almost, the best performance, according to the Ford engineer, is when the PW converted to degrees is split in half and centered overr the max lift. So in essence, half of the PW is in front of max lift and the other is after max lift.

Originally Posted by Sendero

Just out of curiosity, how do you have your tables set. (In terms of Leading or Trailing and the spray event) Didn't you say it helped your fuel mileage and power?

I used TDC and trailing. I noticed about a 3-4 MPG increase. This is with an E303 cam, which does not have much overlap. The only reason I can tink of for the increase is the fuel is not atomizing. It is going in as needed.

[Sendero]

Originally Posted by 86GT

I can not explaine it completley, but I think by spraying early and having it sit on a hot valve will make it atomize (vapor), which in a sense is burnt. It also helps cool the engine.

That makes sense because less combustion fuel equals less emissions. Although it doesn't make much sense for power production. It would seem that they could spray for max power then use the cats to more effectively scrub the exhaust. Either way, thats another thread...

Originally Posted by 86GT

Almost, the best performance, according to the Ford engineer, is when the PW converted to degrees is split in half and centered overr the max lift. So in essence, half of the PW is in front of max lift and the other is after max lift.

That would (if the cam profiles allow) put the piston halfway in its downward stroke. Virtually no way the PW would overrun either event unless they were inproperly sized.

But if the intake is still closed (set to trailing edge and TDC) and the PW is to larger then you would be back to shooting it at the back of the valve. This is not bad because it will have a cooling effect. Which brings another question into play, what negative effects does changing the injector timing have on pre-ignition? Is it possible to overhead the valves and cause detonation (or am I being overly cautious)?

[86GT]

I have not noticed any difference in drivability. It does sound a bit different. I can hear more of the lope in the cam. Temp may have climbed but I can not recall. I was not looking for it.

It will however affect the KAMRF's, mine went down.

[coupe]

Is the injector firing event really that critical when it sits up in the intake stream? I mean: all the factors of valve shrouding, port ineffieciencies, turbulence, inherent misfires...I think your pulse width and pressure are just as critical...unless you have DIRECT PORT injection...man that'd be sweet.

[86GT]

I did not think at first that it made that much of a difference, but once I tried it was evident that it helped my fuel mileage. I can not say that it helped performance any, but it also made the car sound different.

The main thing it gets rid of is the intake wetting. I took my upper off last week so that I could replace the valve cover gaskets and I noticed the intake runners were a lot cleaner than the previous intake I removed. I'm not to sure if this is what made it cleaner, but I think it plays a part.

[coupe]

I imagine it's washing the runner. pressure would also play a key: to get a good spray/mist. That's great to know on mileage though. Very valuable; thanks.