Injector Duty Cycle goes up when on the bottle?

[Super73]

Has anyone else ever noticed this?

Looking at a NA log vs 2 different N20 tunes (57n/35f made 100rwhp, and 70n/42f made 175rwhp). Truck makes 516rwhp NA.

MAP stays the same on all the pulls 97-100KPA. But I noticed a change in Dyn cyl air.
NA = .92-1.05 (Max IDC = 92%) Lambda .78-.81
57n/35f = 1.00-1.13 (Max IDC = 95%) Lambda .756-.805
70n/42f = 1.02-1.17 (Max IDC = 99%) Lambda .738-.805

I was planning on making a jet change to the fuel side, but I think it would be much better to make an adjustment to the VE table to get AFR in line.


My worry is I do plan on turning on the 2nd stage this weekend at the track and I have a feeling IDC is going to go even higher when there is another 175-200hp worth of N20 involved.


I really should think about getting bigger injectors, reducing the fuel side of the N20 jet and increase fuel from the injector, essentially making it more of a dry shot.

[jimmyblue]

Maybe the issue has more to do with the IAT being
chilled, if that's in the path between where the juice
comes in and the TB. Might try to see which of the
sensors is leading the air mass shift (which ought to
be real, that's the whole point of the jug - just get
there by temperature rather than pressure). Question
is, who's seeing whatever's changing - and how right?

[Super73]

IAT is in the air cleaner base. I run a single plain intake and am running a 2 stage NX plate system. IAT is not being effected by the bottle.

Really there are lots of questions..

Who is seeing this happen?
What is causing theirs to do it?

What is causing mine to do it? (Dyn cyl air is the only thing I can see right now)
What things could I log to see the why?

Given the values in the VE table are right to achieve stoich, they tell the PCM how much air is coming in based on a given KPA and RPM. PE once entered is telling the PCM to divide stoich for that given cell by a set number to achieve desired AFR.

I can see MAP changing IDC based on being in a different cell.

How does Dynamic Cyl air change IDC?
I thought dyn cyl air has a relationship with MAP, but could be wrong, perhaps one piece of the puzzle.

What sensors are relative to dynamic cyl air?
What is the math behind it?

[jimmyblue]

Dynamic airflow and dynamic cylinder air mass are
computed with all kinds of fudgery from MAP, RPM,
IAT, some weighted contribution from the MAF
below the transition-to-MAF-only RPM (if you are
still running a MAF not faulted-out). How the air
mass changes, if no real sensor input does, is the
head-scratcher.

Air mass should drive injector duty cycle (or pulse
width per shot, one shot per intake stroke - duty
cycle involves the RPM, PW may be a more appropriate
thing to track or regress against air mass, while duty
probably follows airflow insofar as airflow follows RPM).

We all wish we understood the math, even if we're
not capable of it. Just to see it laid out would be
educational.

I would think that for a given pair of equal MAP, equal
RPM, equal IAT points, that cylinder air mass and the
injector PW ought to be equal as well. But finding two
such, between bottle and no-bottle, might be tough.

What about battery voltage? That gets into the fuel
shot calcs through some injector adder type stuff.
Wonder if that has some deflection when you pull
solenoid power, and bends the injector shot in an
attempt to comp the fuel pressure drop w/ reduced
IGN voltage.

[Super73]

How the air
mass changes, if no real sensor input does, is the
head-scratcher.

I would think that for a given pair of equal MAP, equal
RPM, equal IAT points, that cylinder air mass and the
injector PW ought to be equal as well. But finding two
such, between bottle and no-bottle, might be tough.

Perhaps not that hard. My data shows my no real MAP variance between my NA tune and both N2O tunes. IAT is also consistent as is rpm. This is why an increase dyn cyl air is rather perplexing to say the least.






I have a 1 bar SD OS so MAF is long gone.

I will log voltage, but pretty sure I am not getting a drop, but can't hurt to look.

I am 90% sure I have inj pulse width logged in order to see duty cycle, so I will check that when I get home.

[Super73]

Thought.. N2O is obviously going to put more load on things. Is there any sort of load I could log?

I have a powerglide so all the factory trans sensors are not there.

[Howedeman]

Are you running closed loop or open loop?

[Super73]

O2's are completely disable and strictly open loop.

[Super73]

I did not have voltage logged.

I tried grouping similar RPM sections with each other.
I also looked at +/- 100 rpm to try and find the same MAP reading. I got as close as I could.

The 100 hit layed over a little funny on the dyno at about 6,900 so the 7,1xx reading below really isn't a great representation for the 100 hit.
NA at 6,2xx just did not have a >99 MAP.


You can clrearly see though that Dyn Cyl, IDC, and INJ Pulse go up with the unit for both 6,8xx and 7,1xx. It is interesting though that the 6,2xx mark it looks almost oposite from the snap shot I provided below.


NA/N20 - RPM - Map - Dyn Cyl - IDC - Inj Pulse
NA ------ 7145 - 98 --- 1.02 ---- 92 --- 15.5
100 ----- 7187 - 96 --- 1.05 ---- 91 --- 15.2
175 ----- 7172 - 98 --- 1.12 ---- 98 ---- 16.5


NA ------ 6815-- 98 --- 1.03 ---- 87 --- 15.4
100 ----- 6830 - 98 --- 1.10 ---- 94 --- 16.5
175 ----- 6843 - 99 --- 1.12 ---- 99 ---- 17.4


NA ------ 6421-- 98 --- 1.01 ---- 78--- 14.6
100 ----- 6454 - 98 --- 1.10 ---- 93 --- 17.2
175 ----- 6449 - 100 -- 1.06 ---- 89 -- 16.5



NA ------ 6256 - 99 --- 1.05 ---- 81 --- 15.6
100 ----- 6243 - 101 -- 1.00 ---- 79 --- 15.1
175 ----- 6200 - 101 -- 1.02 ---- 79 ---15.4

[SSUte01]

How are you pulling timing for the bottle? Or are you just running less than optimal on the NA tune?