11.6 desired A/F ratio: isn't that too rich?

[mikeychallenger]

When logging some data on the Predator for my 2009 SRT8 Challenger (93 CAI tune), I noticed that the A/F ratio starts at 12.46 at the start of the WOT run but by 4000 RPM it begins to drop. By 4700 RPM, it has dropped to 11.8 and at redline (6000) it's all the way down to 11.6:1. This is "desired" A/F ratio so why would the tune be shooting for 11.6:1? Isn't that pig rich?

Even with 10% ethanol gas, I'd think something more along the lines of 12.1 would be appropriate. Any info on why the Predator tune is running the A/F ratio that rich?

Mike

[concoursd]

depends on the car and hemis have a tendency to knock so it may not be a bad thing. What really matters though is what your actual A/F ratio is given that you probably have some other mods done to the car.

You can try to lean it out a little and see if the knock goes up on your next log.

[06MonteSS]

the diablo Predator tunes actually lean it out compared to the stock OEM tuning... so just imagine what is was BEFORE you installed the predator tune!!



That's just like the GM predator tunes for the vettes and new camaro's... the predator/trinity tunes lean it out a bunch compared to the stock GM tune, but even then, it is still rich.... to be on the safe side depending on a persons mods they've done to the vehicle...

[brandy16]

The CAI tunes don't lean it out they add about 10% fuel.

[mikeychallenger]

The CAI tunes don't lean it out they add about 10% fuel.

Why would a CAI tune add fuel and a non-CAI tune remove fuel? Doesn't make sense. The MAF is going to read the proper amount of air regardless of what type of intake is on the car... and I'd think DiabloSport wouldn't add fuel to a CAI tune just because it has a CAI.

Edit: I should clarify... I can see the absolute amount of fuel needed being higher, but the desired A/F ratio shouldn't change (over the non-CAI tune). At least in theory.

Mike

[06MonteSS]

so then that there inspires a question....

does mikeychallenger have a good CAI on there to provide enough adequate airflow to be using the CAI tune that compensates for it???

heh...

[SRT8Tech]

Well first, an SRT8 or any Challenger or Charger doesnt have a MAF sensor. They use a speed density system. Actually no Chrysler Dodge Jeep product has one on them now. I believe only the Dodge Stealth had the MAF on it. Second, the CAI tune adds fuel because the CAI lets a tad bit more air in so you need to add a little fuel for that extra air. Thats that basics of it. The "desired" AFR should be close to what the real AFR is. I would still put a wideband on it just to see what the true AFR is though. My 07 SRT8 Charger liked 12.2-12.5 the best.

[mikeychallenger]

so then that there inspires a question....

does mikeychallenger have a good CAI on there to provide enough adequate airflow to be using the CAI tune that compensates for it???

heh...

Dunno. Since CAI is a generic term and there are about a dozen out there with all different levels of effectiveness, I'd assume mine is OK. Doesn't change my question about desired A/F ratio. The MAP sensor should account for the CAI anyway, so I'm not really sure why we have different tunes for CAI versus non-CAI. Speed density systems should be able to compensate for any change unless it is after the intake manifold so it should automatically pick up the change in MAP readings caused by a freer flowing intake system.

My main interest is finding out why Diablosport thinks a rich 11.6:1 A/F ratio is needed in higher RPM. Is it really necessary, or shouldn't we be shooting for an even leaner mixture? I could restrict my intake down to the width of a pencil and it still won't change the fact that the 93 CAI tune on the Predator is still going to command a rich 11.6:1 mixture because that's how it is programmed.

Mike

[concoursd]

not really, the MAP is going to rely on the V/E tables. On speed density, if you alter the volumetric efficiency then you will need to compensate for that. And of course, if you change cams to radical ones, you throw the manifold vacuum levels out of whack for the MAP sensor.

MAF is superior in that regard as it will adapt to air flow increases and cam changes easily as long as the MAF sensor/housing is properly calibrated and accurate. Speed Density has its own advantages too though.

I had to switch to MAF on my old 87 5.0L from speed density for that very same reason. When I added exhaust and intake upgrades it was fine except I had to up the fuel pressure a little. Then, when I changed heads and cams, I had to switch to MAF to get to run great. Luckily for your dodge guys, there is plenty of ability to tune your cars with speed density. Back then though, nobody wanted to touch speed density and tuners just told you to upgrade to MAF to make tuning much easier.

[mikeychallenger]

not really, the MAP is going to rely on the V/E tables. On speed density, if you alter the volumetric efficiency then you will need to compensate for that. And of course, if you change cams to radical ones, you throw the manifold vacuum levels out of whack for the MAP sensor.

That I understand. The cam is "downstream" from the MAP sensor. Changing anything upstream of the MAP (ported intake manifold, bigger throttle body, better flowing filter, filter box, or CAI) should all be picked up by the MAP sensor and those don't change volumetric efficiency.

So you shouldn't need any changes to the speed density table for installing a freer flowing air intake box or air intake tube. Unless I'm missing something?

Mike

[Animal451]

Question:
Does your A/F get rich in every gear around 4000 rpm? Mine hits 4000 in 3rd gear and gets pig rich. It hits the cat overtemp and adds fuel to cool the cats. A tuner can raise the threshold if that is the problem . . .

[mikeychallenger]

Question:
Does your A/F get rich in every gear around 4000 rpm? Mine hits 4000 in 3rd gear and gets pig rich. It hits the cat overtemp and adds fuel to cool the cats. A tuner can raise the threshold if that is the problem . . .

Every gear. I'm familiar with the cat overtemp. I haven't hit that yet, which is good. If I'm running at highway speeds and then just stop and do a wot run, I get a start at 12.46 and by 6000 RPM it has dropped to 11.56. If I do four more back to back WOT runs without cooling off, I get the same: 12.46 to 11.56 at redline.

I actually made some calculations and adjustments via the WOT fuel and on the first try, I got it to hit exactly my intended range: 12.8 at low RPM dropping to 12.0 at 6000 RPM. Didn't seem to do anything either for power or knock so I set it back to the original figuring Diablosport knows more than I do.

Plus... I read in a thread that I found by Googling that the Hemis like a fuel mixture in the 12.2 to 12.6 range NA. Of course, the problem these days is that you don't know whether that 12.2 to 12.6 has already been factored for 10% ethanol since that's all you can find these days... or if those are the "pure" gas numbers. If they are the pure gas numbers, then the range for 10% ethanol gas would be 11.7 to 12.1 which is actually closer to what the Predator is using.

So many variables...

Mike

[concoursd]

not really, the MAP is going to rely on the V/E tables. On speed density, if you alter the volumetric efficiency then you will need to compensate for that. And of course, if you change cams to radical ones, you throw the manifold vacuum levels out of whack for the MAP sensor.

That I understand. The cam is "downstream" from the MAP sensor. Changing anything upstream of the MAP (ported intake manifold, bigger throttle body, better flowing filter, filter box, or CAI) should all be picked up by the MAP sensor and those don't change volumetric efficiency.

So you shouldn't need any changes to the speed density table for installing a freer flowing air intake box or air intake tube. Unless I'm missing something?

Mike

The cam swap "can" create volatile vacuum and since the MAP sensor is a vacuum sensor then it will throw off the idle and cause other driveability problems like stalling when coming to a stop. As I said before, after modifying a speed density car I am pretty familiar with its needs.

Any time you increase the volumetric efficiency through any modification whether it be cylinder heads, intake manifold, or cold air intake, some cars may need to be retuned since the MAP sensor USES the v/e tables. If the v/e tables are off, then it is like having a MAF calibration curve that is off on a MAF car.

When the cold air intakes are put on a stock hemi, it leans them out, but usually not enough that the stock calibration file cant handle since it is already running rich. When you stack that with a predator tune, you get a mixture that is too lean.

[director1203]

Ineresting conversation here. I have been trying to get my SRT4 to run much richer, but cant seem to get the needle to move off of 14.37. I have already added 20% more fuel at all WOT levels, but it hasn't made a bit of a difference. Any ideas what i can look for or change to effect the A/F levels.

[concoursd]

the first issue could be your tune changes not properly writing to the pcm. I would export your last tune written and having somebody at diablosport look at it.

You may also have a fuel supply issue (maxed out fuel pump or injector duty cycle) or possibly a sensor issue that is not letting the pcm know that extra air is entering in the motor like maxing out your MAP signal.

Maybe somebody more familiar with the SRT4 could chime in?