from past experience (WRX's) increasing the diameter of the MAF housing can cause the car to run lean. does the G35 run a closed -> open loop fuel program? meaning, below certain loads it constantly monitors AFR and adjusts and switches to pre-programmed maps at higher loads? if it does it can cause the lean conditions we got on wrx's, if not then the ecu should compensate.

 

The question is at what MAF voltage does the ecu top out at [injector open time].
Something shy of 5.000000 volts.
Lots of difference between 4.444 volts and 4.65 volts maybe 20% more fuel.

Extremes of temp from 60F [SAE nominal]say -30F [would be 90/11= 8.2%] density increase as wouls 150F [150-60=90 delta] -8.2% decrease.

ECU expects nothing more than + or - 15% plus barometric decreases [Denver].....Sealevel in Alaska winter to mountain top summe ... might be 30% less dense. Obviously a MAP [manifold actual presssure] sensor is helpful to decide you actually are in the mountains vs a air bypass of MAF leak.

Would be great to see a MAF voltage vs CFM or grams per second flow rate graph?

 

So...all other things being equal, all we need is a touch more voltage at the MAF wire and we're adding more fuel (ie--running richer)?
Well, it's time to rig up some AA batteries and see what happens!

 

why would you want to run richer? for forced induction, absolutely, but whatever kit used should come with some sort of engine management.

a SAFC or Unichip would take care of altering the MAF signal for you if you really wanted to mess witht the fueling.

 

I'd like a little bit more fuel for some intake and exhaust mods. Yes, a reflash or SAFC or whatever would do the trick, but if there's another way, I'm open to ideas.

 

have you had your car on a wideband, sometimes more fuel isnt always better

 

yes, too rich is not a good thing. with say an intake and an exhaust, your engine will pump more air, and the ecu will detect that via the MAF (unless the intake alters the diameter of the MAF housing) and adjust fuel appropriately. there could be to gain through tuning, but most likely it would be gained by leaning it out a little.

 

No, I have not. I've only had several tidbits of advice that I'll run lean with high flow cats and a plenum as my only mods. True--I really need to do a "before" dyno, add the mods and then dyno again.

 

Hey Guys

OK...here is the deal. I know that the stock 6MT (with many post-maf mods in this case) MAF will top out at 4.5v (never in the 4.6+ range). Increasing the diameter of the tube is exactly what I was trying when i blew my engine... Altough it wasn't exactly done right yet (we were in the process), the 4" ID (up from the 2.6" ID of the stock plastic) made about 0.2-0.3 volt difference near redline at about 9-10 psi of boost. This made a tremendous difference in a/f... I was lucky not to blow my engine right there ad then during my first test run. The a/f went from 9-10.5 AFR to about 15 AFR! Now... there are a couple of possible reasons for this: it could be the turbulence created by the sudden 2.75" to 4" transition (and the MAF was sitting only 1.5-2" dowstream of this transition) that caused the lean condition, or, more likely, the shift in voltage itself. Either way, the presence of turbulence is a fact, as I was logging maf voltage and the relatively smooth MAF voltage curve got much 'noisier' right after the new housing was installed. If it's the change in MAF voltage that caused the lean condition, something that I think was the case, then changing the diameter of the maf housing is going to require a complete remapping of the ECU.

The only reason to do this is to gain range in the MAF sensor, at the expense of resolution. Otherwise, do not mess with it...just not worth it. I will keep you guys updated of what happens with my tuning.

Gurgen

 

it's not likely to be the turbulence of changing diameter drastically, it's simply because the diameter was changed. the MAF sends a voltage signal, but all that really is is CFM, and since the CF part is constant, the voltage correlates to the velocity of the airflow. change the diameter, and at the same airflow the velocity is lower, so the voltage is lower. your ecu (if not adjusted) thinks that you are pumping a lot less air through the engine than you really are.

what were you using for tuning to compensate for the larger tube? if you only changed the diameter of the MAF housing that'll do it.

 

"the MAF sends a voltage signal, but all that really is is CFM, and since the CF part is constant, the voltage correlates to the velocity of the airflow. change the diameter, and at the same airflow the velocity is lower, so the voltage is lower. your ecu (if not adjusted) thinks that you are pumping a lot less air through the engine than you really are."

Wow you said what I wanted to say up in #3 above.

 

So i guess running at higher voltages actually justifies the expense of the modifications to the intake system. I doubt it's worth doing much more in the way of modifications if you get to 4.96. Rip those power ducts off, guys and get rid of all of baffles in the system by getting the Z tube and tearing out the drain catch below the airbox.

NEVER BEFORE REVEALED SECRET: The hole that goes into that catch is wide open and sucking in additional air forced in from below where I ripped out the foam down in the bumper for the old Injen setup. Ha I actually dount that much air is coming into the engine from that hole. But Why F with it now?

 

gurgen, i dont understand what you mean by using a transition. Did you actually cut the tube out from around the mafs, then drill a hole in a larger pipe and insert the element in there (what i described)or did you do somethign else

 

black bird, that's exactly what i did. We made a transition from 2.75" to 4" (about 4" long) and back down to 2.75".

Also, there was definitely a lot of turbulence there. The maf voltage was not only lower but a lot noisier!!! The MAF voltage trace was jumping up plus/minus .2 volts instead of the usual amplitude of less than .1 (at idle).

 

i dont understand why you'd need to go to such an extreme ID size. at that point why wouldn't you just go with a set of bigger injectors and some sort of piggyback, or just elimnate the mafs all together and use a MAP with a standalone, I understand cost is an issue but it probably ended up costing alot more when you blew it up