Roadracing7

iTrader: (2)

(Bad internet connection, reposting)

After reading all I could on the subject and talking to RC, when I installed my 1300s, I ran .20 on the lag time correction on the secondaries and changed the injector volume to 1300.

There is a lot of contraversy about lag time though. RC says their injector driver gives them a lag time of .43 on the 1300 injectors, but after talking to various tuners, RC recommends that RX-7 owners (specific to injector drivers from the Power FC) run .20-.25. In the Power FC Manual, it states that stock injector Lag Time is 0.77msec, and that whenever changing injectors you take the new lag time and subtract the old and that is your adjustment to put in for lag time adjustment. If this is true, the .43 (assuming it's the raw lag time RC is receiving) would give -0.34 (0.43-0.77). I asked what the difference was between the two lag times recommended to run and was given an answer VERY discomforting. ".01 and .02 lag time has a difference of 1% fuel..." So from the .16 that Jason is telling people to RC's recommendation of .25, there is 9% fuel difference... This is taken strictly from what I was told by RC Engineering.

What to do about it? Pick a lag time you are most comfortable with (bigger the number, richer it will be initially). Leave that lag time the same from here on out and get to a wideband to retune your car. You cannot simply drop in the injectors, plug in some numbers and hope to be running the same AFRs according to this information... I plan on taking the safe route and retuning or at least double checking to see if AFRs are still okay.

Richard

PS- Someone please correct this if the information I was given is incorrect.

rotorbrain

why are the lag times differing so much. this should be a straight forward answer. id say go with what rc is giving as a lag time on the injectors. id like to know why rc even recommends to go with a different correction than what the manuals equation states it should be. im assuming to smooth out the pri/sec transition. am i right in saying that the lower the lag time the sooner the injector comes on, meaning the two sets of injectors start working together faster. in that sense, lag time doesnt really even matter if you compensate with the correct tuning in your fuel maps. keep the lag time low and then take some fuel out.

or is it by setting the lagtime to the number that your equation gives you, you are "telling" the ems that this is how long it takes for this injector to start working in relation to the one that used to be in there. then the ems makes a correction that we dont see or set. in that case i would much rather follow the equation developed for this process.

anybody care to shed some light?. . . or am i just that much of a confused little boy? haha!!!

paul

Badog

I have always used .20 for the RC bored 1300s.

Roadracing7

iTrader: (2)

RCs description for what lag time is, is "The time it takes for the injector to reach full open after getting the signal." With this definition, I would assume that when telling the ECU that the injector takes longer to fully open, it would either send the signal earlier or later for the 1300s (which take longer to fully open than stock). Earlier or later does matter either way, it's constant and is corrected in tuning. When you put .20 in for the lag time adjustment, you're saying that the new injector takes .20 msec longer to open relative to the 850s that came out. If you tell the ECU that it takes the same time as the 850s to open, the "stock" signal the ECU is sending your 1300s does not allow the injectors to fully open, and you sacrifice a certain amount of fuel because of this. In other words, you're lean! Since RC told me .01=1% fuel, I think the amount people are varying in lag time on these injectors (as well as any other injectors controlled by the PFC) is enough to totally screw up fuel map comparisons and potentially pop a motor that ran safe on the stock 850s.

Do you agree with me that the 9% of accepted error in fuel is something serious enough to bring attention to the necessity of tuning after injector swap?

Richard

cewrx7r1

iTrader: (2)

From an old post of mine: no one has yet proven if lag time adjustments affects the timing of the injector signal from the PFC or the pulse width. All so far is hearsay from us, nothing from Apexi.

I tried to measure it with a scope but could not get a clear and steady trace. The scope was really for RF frequencies, not for slower square wave signals.

Here is a thought. Stock 850s bored to 1200 by RC, like mine, are suppose to have a slightly larger lag time.
I am using +.1. But they can flow 40% more fuel, thus for the same fuel flow, even if they open slower, they pump the fuel faster. So what is the overall affect on injection timing? No way we can test that, maye RC could.

SPOautos

I can tell you this, when I changed my pri injector lag time setting from 2 up to 8 my a/f went from 11.5ish up to about 12.1ish with NO other changes. Thank God I was checking this at a lower rpm.....which I did on purpose in case it made a big change in a/f

I droped it back to 2 and my a/f went straight back to where it was.

I cant give a good explanation of what those corrections do but I definatly know they can drastically change your a/f and you dont need to mess with them unless you have a wideband hooked up

STEPHEN

RX794

I wish Ralph from Xcessive could explain what this does, he knows EXACTLY what this is and how it works.

Roadracing7

iTrader: (2)

And..... CUE Ralph...

SPOautos

If Ralph didnt explain it to you how do you know he knows exactly what it is??? Anyone can crack open the PFC manual and get the correction formula.

Here is the problem, if you tune your car, THEN you change the lag time settings as far as I'm concerned you just ruined your entire map. One they are set you cant change they or else you run the risk of changing your a/f ratio.

STEPHEN