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Old 11-04-2005, 11:29 AM   #1
RainMaker
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Now with alot less verve!

Default Tuning and the BigMAF

Hey all,

Tim B from PDXTuning and I have been working on the drivability of my combo. Its a 3" green with a 3" Turbo inlet and a Perrin BigMaf. Also, theres a TubroXS FMIC in there. Tim's using ECUTek for tuning.

There have been two drivability troublespots for us. The first is around idle quality. Its taken a slight hit with the new combo. Secondly, there is some light hesitation/tip in surge between 1800 and 2900 rpm. This isnt BAD hesitation, but I drive in traffic a bit everyday, and I like a smooth ride. Coffee drinking smooth.

Given some initial problems that I could recognize from the old Mustang days as MAF turbulence, I built a 3" cold air setup for the car. Quite a Frankenstein, but in the end pretty effective. It made a good decrease in the 1900-2900 issue, but the idle still seemed off. I feel pretty strongly that the Perrin BigMAF filter is not creating proper laminar flow. Putting it way down the pipe, while possibly restrictive, does seem to create some laminar airflow consistency.

In this position, we then went about doing some dyno tuning. With the ColdAir on the BigMAF, it made great power and actually had a slightly smoother MAF transfer curve than a typical shorty BigMAF.

Next, we did some on-the-road tuning to try and see what the MAF and airflow were doing during the hesitation. The car had apparently learned to throw in the max +25% fuel at the particular spots that it hesitated. Also, during an un-accessable tip-in routine, it would add even more fuel... thereby creating (from what I can tell, an XD-1 is going on this weekend), a very rich situation (ie hesitation). The tip-in hesitation was bad, but the drive-through constant throttle hesitation was only mediocre. So Tim went about altering the MAF transer fuction to get it off the rails where it was richening up. This has helped the smoothness through this area, but it's not perfect. I'd like to keep working on it. We could not do much for the idle, since EcuTEK hasnt worked out those tables (presumably just like the tip-in enrichment routine).

Then last night, I had an idea from the old Mustang world and took some screwdrivers out to the car.
By clocking the MAF (rotating it within the couplers), I could make a *sizable* improvement to idle and unfortunately, a sizable degradation of the 1900-2900 rpm issue. I finally settled in a place that has the idle a bit better, but has the 1900-2900 issue a little worse/the same. What I'd like to do is get together with Tim B and see if we can look at the logs to determine where the MAF works the best.

I'll take a picture soon so that y'all can see *where* the MAF is. Its about 8 inches in front of the Turbo Inlet, adn about 12 inches from the 90 degree bend going into the fender.

There has to be an optimal solution yet, but I sure would like a few tuning parameters from EcuTEK...

1. Idle ignition advance. Increase the Ignition advance in the upper left spot on the ignition map thats avaialble all you want and the idle advance doesnt change.

2. Tip in Enrichment. We need access to whatever additional duty cycle offset and timing is there for the accelerator pump effect.

3. Open-loop/closed loop threshold (could be several factors...)

4. Long Term fuel trim cell boundaries. Maybe this is just fixed, but informational. Transistions between cells can make for some rough running if they are adding or removing fuel differently enough.

thats some info and my wish list.

Lastly, I'd like to discuss using a Ford 90 or 95mm Cobra or Lightning MAF in our cars. They too are 0-5 volts, and Ive heard they can be purchased for ~$100. Once someone works out the transfer function and a temperature sensor issue, these may be a cheap solution for cars that max out the stock MAF but want little or no turbulence (assming a decent intake tract).

Then again, maybe I just need to go blow-through and quit my bitching

-chris
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Old 11-04-2005, 11:39 AM   #2
AaronWRX
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Quote:
Originally Posted by nmyeti
There is a very nice solution in the works that does not require any additional electronics or expense. You guys will see it first in the 350z market with the introduction of the UTEC over there. They max out their MAF sensors very early. I’ll say nothing else other than to suggest you sit tight.
I can't wait to see what this is about.
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Old 11-04-2005, 11:46 AM   #3
RainMaker
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Now with alot less verve!

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Well, I would guess that it may relate to the MAF-Xformer or whatever capability. Alot of folks who think they max out the MAF on Fords actually only max out the input range of the computer. The MAF puts out in some cases as high as 7.5 volts. Meaning of course that theres headroom to be spared if the computer could only be convinced to input up to 7.5 volts. The MAF-Xformer or whatever it's called is only a voltage splitter and transforms 0-7.5 or whichever to 0-5 volts.
The question becomes "could out subaru MAFs actually put out more than 5 volts for increaded headroom?"
Even if the answer was yes, doesnt the small stock MAF size create a restriction that isnt ideal? Perhaps in blow-through applications where the air is more dense, it's not such an issue... but on the atmospheric side of the turbo, a big maf housing that works well is going to be less restrictive and make for better spool/powah.
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Old 11-04-2005, 12:04 PM   #4
ataac_flat04
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Going against the "less flow restriction" grain, but have you tried a MAF screen? Something like what GM puts in front of their MAFs for "laminar flow". Usually they are the diameter of the MAF and about 1/2" thick honeycomb. Cost about 5HP on a NA application like LT1 in a F-body or Impala. Also I wonder where the sensor is in relation to the center axis of the pipe on a BigMAF housing relative to position in the pipe of a stock MAF housing. If it's too far off center, I would be inclined to say that may be having an effect on sensor readings as much as lower air speeds would. Somewhat supporting the evidence that when clocking the MAF gives different drivability results. -Chuck
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Old 11-04-2005, 12:14 PM   #5
RainMaker
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Ive thought alot about the screens.. I took one out of my SS years ago

The problem is that most folks that I know of a) dont remove them eligantly (in one piece) and b) dont keep them.

From what Ive worked out, they are not available individually from GM. Just as part of a new MAF. I dont need a GM MAF
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Old 11-04-2005, 11:00 PM   #6
RainMaker
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And this car keeps changing as the long term fuel trims rise and fall in different places It is pretty important to monitor and log after each change... even if just clocking the MAF.
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Old 11-05-2005, 03:50 PM   #7
RainMaker
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And now that the weather just changed, I bunch of things changed with it.

Are others experiencing hesitation and going lean/rich with the BigMAF during normal driving?

chris
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Old 11-08-2005, 01:48 PM   #8
RainMaker
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Now with alot less verve!

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Anyone???

Bueller....
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Old 11-08-2005, 03:10 PM   #9
mrbell
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This is something we've seen. We believe the neck down immediately after the MAF sensor is the root of the problem. Unforunately there is no real way to fix it in tuning, I don't believe. At certain points under different conditions that the computer can't distinguish, it needs to do different things.
The honeycomb idea might work after the sensor to prevent reversion, or the MAF could be moved farther from the neck, but I don't know if anyone has actually tried such a solution.
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