Compensating for injector latency using AFPR and AFC

[imdrax]

I figured my posts were clogging up the Evo vs Montero Maf post and figured since I can't find much info I would start a thread of my own.

Im running, in essence, an EVO8 MAF(#501 w/ airhorn removed). Today I swapped out my 560cc EVO8 injectors for 720cc Denso injectors. Over on EVOm I was able to find out that the deadtime for the Denso injectors at 14v=.96ms. The closest number I was able to find out on the stock 450's was .5ms? In any case the increased latency is causing me headaches to tune. I wanted to be able to tune strictly with my AFC and AFPR because this is my DD and can't throw any more money into it at the moment. Has anyone had any experience with these injectors using a stock ECU?

Currently I have the AFC 1000rpm settings at +30% and LO setting around+25% in order to maintain a steady idle and cruise around 14.7AFR. I didnt have much time to mess around too much because I had to goto work. My main concern is that the increased latency obviously has a much larger impact at lower IPW and without having the ability to adjust for deadtime values my tune will be sporadic at best. What would you recommend as starting values for my high settings? Certainly i would not think to ad +30% but then again I would rather not make a pull zeroed out and run lean.

I will try to up my base FP tomorrow and see if I can pull back some fuel via AFC. Any input is appreciated

 

[Demon33]

Using the AFC and AFPR there is no way to compensate or adjust for the increased deadtime of the larger injectors. The deadtime definitely has more of an affect at lower IDC's, but it still has an overall affect on tuning. It's difficult to say what you should start at, but I'd suggest starting from a rich point and tune towards your ideal setting.

If you have an EPROM ECU, I would also suggest getting an EPROM chip programmed for your current mods. It's relatively low-cost and will account for the increased deadtime over stock as well as the injector size (global fuel) and any other mods you might have. Plus, you get a few really cool features like stutterbox, NLTS and more.

Right now, your best bet is to put the evo560 injectors back in, as they have a deadtime more similar to stock and you'll probably have an easier time tuning with them. Of course, your e316g can probably max them out especially on our 91 octane which we have to run a little richer to prevent knock. Just keep the boost and IDC's within reason and watch for knock.

 

[imdrax]

The car does have an EPROM although it is not socketed. If I were to go through the trouble of getting it socketed I figure I might as well pick up V3lite for 345 because JeffO chips are $140. I ave had multiple cars chipped by Jeff and my roomates GSX is done by him and runs great with no AFC, but I am going to try and tune with the current setup. Im sure its possible to get the tune I want its just going to be harder and more time consuming. The 560's are already in the mail to their new owner. I had them tuned very nicely @ 18psi on 91oct no knock but I was nearing 90%DC. I would like to run 20psi safely on the street and around 25psi when I goto the track.

 

[jeffo]

IMO, between the 3G MAS and the 720cc injectors, you are going to be removing way too much airflow signal to get a decent tune. You will have WAY too much timing advance, unless you are planning on running racegas.

 

[Demon33]

IMO, between the 3G MAS and the 720cc injectors, you are going to be removing way too much airflow signal to get a decent tune. You will have WAY too much timing advance, unless you are planning on running racegas.

Jeff speaks the truth. As you pull more and more airflow signal with the SAFC you are also telling the ECU to move into lower and lower load ranges in its lookup tables. As load is decreased, timing increases. You may in fact be at the proper AFR to prevent knock, but your highly advanced timing will in itself induce knock, adding another variable to your problem.

We all know that the SAFC has no way to control timing directly, but we can do it indrectly. With the proper deadtime and global fuel accounted for (ie, reprogrammed EPROM), you can actually use the load vs timing to your advantage. If you increase your fuel pressure a little and take away some airflow to compensate, which moves the load to a lower range, the end result is the same AFR with an increase in timing. The reverse is true as well- reduce fuel pressure, increase airflow and the timing will decrease.

A drawback to this method is that you have to make compromises when tuning, as changing fuel pressure affects the AFR at all rpm and load ranges which makes tuning a specific rpm or load point without affecting anything else nearly impossible, but I ran this way for nearly a year without issues. With about 20 PSI boost, I saw 19 degrees of timing at the top of 3rd.