Do I have to trick the MAF for boost??

[Shane]

am i going to need to do anything to trick the MAF to run liek 10psi?

[Dominic]

nope, it will read the flow properly probably up to a limit. I dont know what that limit is but its likely not near 10psi.

[nocutt]

<blockquote>quote:</font><hr>Originally posted by Shane:
am i going to need to do anything to trick the MAF to run liek 10psi?<hr></blockquote>

I don't know what you plan on doing for Fuel management, but running "boost" thru the 3800 MAF/TB is not a great idea without recalibration...

[Arctc Wolf]

it should be fine, as long as u don't go crazy w/ bigger injectors. the car's can handle a 2-3 lb. increase in fuel injector size, but not too much more than that. Also, the MAF is only used while the car is warming up. once it's warm, the O2 sensors determine the proper A/F ratio, and adjust injector pulse width accordingly, whether u have bigger injectors, boost dependent FPR, ect.

[nocutt]

<blockquote>quote:</font><hr>Originally posted by Arctc Wolf:
it should be fine, as long as u don't go crazy w/ bigger injectors. the car's can handle a 2-3 lb. increase in fuel injector size, but not too much more than that. Also, the MAF is only used while the car is warming up. once it's warm, the O2 sensors determine the proper A/F ratio, and adjust injector pulse width accordingly, whether u have bigger injectors, boost dependent FPR, ect.<hr></blockquote>

Arctc I beg to differ...a 2-3lb difference in injector size wouldn't really matter as far as fuel enrichment is concerned...simply put, it isn't BIG enough for what he has stated...
without getting too technical the MAF is ALWAYS used to ascertain what amount of fuel to provide the engine at the correlating "mass" air flow, in accordance to several sensors which is ultimately determined when the system is in either close-loop or open loop. One doesn't really care about close-loop when power enrichment mode is called upon. At WOT o2 sensor readings are non-consequential (as far as determining the correct AFR to run the engine as in closed-loop)...but MAF/MAP readings better be!! Unfortunately for boosted application our (3800S2) MAF/TB is not a "true MAF"...since the sensor "isn't really" reading the air flow but rather sampling and taking a differential (look at the design you will understand). Yes you can put pressure thru it but the hardware isn't really rugged like say an LS1 which is actually opened and in the airflow path...put pressure thru a 3800 MAF/TB without a recal...the engine will have the tendency to be inconsistent and run lean. The point at which the MAF tables run out of calibration is beyond me...I have never seen the MAF tables but I know that it isn't a wise decision. Now if you plan to run an FPR (FMU) the tables are a bit different still it is a band-aid!!?!?

[Arctc Wolf]

at 10 psi, our cars still have been able to run on stock injectors. also, I believe that flow increases exponentially as pressure increases, so 55 psi on 22 lb. injectors will flow a lot less than 55 psi through 24 lb. injectors. oh, and as far as the maf is concerned, u can always get a VPC and disable the MAF entirely.

[Tiago]

our turbo kit runs boost through the maf, seems to work fine. ;)

[nocutt]

<blockquote>quote:</font><hr>Originally posted by Arctc Wolf:
at 10 psi, our cars still have been able to run on stock injectors. also, I believe that flow increases exponentially as pressure increases, so 55 psi on 22 lb. injectors will flow a lot less than 55 psi through 24 lb. injectors. oh, and as far as the maf is concerned, u can always get a VPC and disable the MAF entirely.<hr></blockquote>


@ 10psi no car is running on 22lb injectors and the stock fuel system and/or stock fuel calibration!
BTW a VPC is a AFR calibrator in other words it "tricks" the PCM and can "make" a MAF work like speed density..."it doesn't get rid of the MAF" without a reprogram at least. Also GM MAF sensors are calibrated to work within a given range 0-~5V nothing before or beyond this can be recognized...simply put with a MAF (AFR) recalibrator a 3800S2 can only accept up to 28-30 lb injectors (without a PCM reprogram)...anything above this will kill idle and low RPMs...

Tiago...if you are using an FPR (FMU) you can get by *blowing thru...but think of it this way...
Look at the way the 3800 MAF/TB works it takes a sample of air thru a small hole via a housing, which is in turn directed towards the bottom end which has a slit...the element isn't in the air flow but in the that small housing...Now how in the world can you tell me by blowing thru this MAF, it can actually tell you the amount of or the volume of air going into the engine and let even assume it works like a "true MAF" the housing itself can be heat soaked in a matter of seconds with boost...can we all say inconsistency!! On the other hand, if you are using an FMU, then this theory is different, because now you are using PSi as a reference and not worried about the flow*

*For the physicist or aerodynamist...if you put pressure within the confines of say the intercooler outlet to the TB (yes the whole system is pressurized and pressure drop is not consequential...this is ONLY AN EXAMPLE). We are using 7psi...therefore "in-theory" the outlet of the IC to the TB should have 7psi...in a NON-pressurized setup..Of course this means NATURALLY ASPIRATED...the engine gets air thru ambient pressure so therefore if "vacuumn" has been created to suck air into the engine everything behind the TB should have 0 psi, while the front of the TB should have ambient pressure therefore the pressure differential helps pull air thru the MAF/TB...now put the example into our pressurized system...with boost..pressure HAS to be every where in the intake...even behind the TB...so if the back of the TB has 7psi and the front has 7psi...why will air want to go thru the MAF housing?!?!?!?!?
Oh yes you can take the backplate off...now you have skewed the MAF readings, your non-boosted drivability WILL be affected, because now you are running lean...On boost, no predictabilty and inconsistency!!

[Riles]

<blockquote>quote:</font><hr>Originally posted by nocutt:

Now if you plan to run an FPR (FMU) the tables are a bit different still it is a band-aid!!?!?<hr></blockquote>

Why would an fmu be a band aid for low boost situations? The powerdyne unit includes an FMU that raises fuel pressure to 60-70 psi. Thats only a little over a 10-20 psi increase. Running your system at 10 extra psi won't hurt it, ever, and your fuel problem is solved. Band aid? More like surgery.

[Tiago]

the FMU is a BANDAID, but it works great.

[nocutt]

<blockquote>quote:</font><hr>Originally posted by Riles:


Why would an fmu be a band aid for low boost situations? The powerdyne unit includes an FMU that raises fuel pressure to 60-70 psi. Thats only a little over a 10-20 psi increase. Running your system at 10 extra psi won't hurt it, ever, and your fuel problem is solved. Band aid? More like surgery.<hr></blockquote>


Running an FMU DOESN'T give you the proper characteristics associated with "REAL" drivability...you see when the fun starts you will come to see that raising fuel PSi/lb of boost is indeed a bandaid...the mathematics exist, there is more to it than your "60-70psi"...nothing wrong with low boost situations but once you start to exceed the limits... :eek:

[Wicked 3800 V6]

Aight folks, give me an answer. I'm running 7-10 lbs of boost, what do I do to the MAF and fuel?
FMU?
VPC?
S-AFC?
AFPR?
Bigger injectors?
Nothing?

[Shirl]

All of the above [img]graemlins/rofl.gif[/img] no one really knows for sure. Experiment and give US the results :D

[nocutt]

<blockquote>quote:</font><hr>Originally posted by Wicked 3800 V6:
Aight folks, give me an answer. I'm running 7-10 lbs of boost, what do I do to the MAF and fuel?
FMU?
VPC?
S-AFC?
AFPR?
Bigger injectors?
Nothing?<hr></blockquote>


Without making this another long winded conversation...If you are going to blow thru then becareful...too much inconsistencies, also more inconsistency when you use a black box that uses the MAF signal for data (basically anything that tricks the PCM/MAF). Don't get me wrong it might work for you but still it is wrong data...period! IF you are going to use a suck thru...you give up some throttle response (little) but this is usually the most prefered choice on most turbo setups...now you can also use a blow thru MAF...a "true MAF" ls1, Lt1 but then you will need to recalibrate the MAF. To run bigger injectors you will need a reprogram or recalibrator...with a recalibrator you can only run as much as 28-30lb injectors but this works well for 7-10 psi of boost. An FMU can be used, like evrything else it isn't for everyone...plus this works very well a the drags...where WOT is engaged within seconds...for road racing, you need consistency...therefore and ultimately a reprogram is the best where you can get a better MAP of fueling and igntion needs...beyond that the rest will lie on those you have the best data for consistency in ALL FIELDS not one...