Tricking Std Maf Power Fc To Use Map Sensor

[h2k]

Alot of people max out a MAF setup with the powerfc. The Q45 maf can't make as much kW as im running.

The maf has 3 wires:

12volt IN

Ground

Signal out(0.2 to 5.2 volts)

Now I've found a Motorola 2.5BAR MAP sensor wich has 3 wires:

MPX4250A series

12volt IN

Ground

Signal out(0.2 to 4.9 volts

Now im might be thinking way to simple, but WHY should it not work to use this map sensor on a completly regular Apexi Power FC and feed the map sensor signal into the afm wire. In simple terms, to convert the MAF to MAP system and remap the ecu with new voltage values depending on load.

Can anybody explain to me if this would not work, why should it not?

[rinmak]

Doesnt MAP require an air temp reading as well that it uses to calculate the final air flow figure?

There would be no input/function inside a regular PFC to calculate this.

[paulr33]

its been tried before and doesnt work

1) run twin maf sensors

2) sell it and buy djetro

3) move maf sensor into larger shell for more scale

4) try hks vein pressure converter (legacy product)

[paulr33]

be sure you understand the full mechanics of mass pressure reading vs mass flow reading

and that you are measuring the same thing but in two different methods

one is reading volume and one is reading pressure and guessing

be sure to note that a 2.5bar map sensor is really only 1.5bar boost

as 1bar is negative vacuum so keep that in mind too

also to note that once boost peaks at your boost controller set, so say 1.3bar

that pressure remains fixed at 1.3bar and more and more air comes into the engine

so you loose tuning accuracy also - runs along horizontal axis

[discopotato03]

Yes agree wholeheartedly , manifold pressure can be constant while the volume continues to climb .

In that situ with a MAP sensor load based system once the throttle is fully open all you have to tune with is the RPM and temp sensor signals - so 2D at best .

A .

[Gav]

be sure you understand the full mechanics of mass pressure reading vs mass flow reading

and that you are measuring the same thing but in two different methods

one is reading volume and one is reading pressure and guessing

be sure to note that a 2.5bar map sensor is really only 1.5bar boost

as 1bar is negative vacuum so keep that in mind too

also to note that once boost peaks at your boost controller set, so say 1.3bar

that pressure remains fixed at 1.3bar and more and more air comes into the engine

so you loose tuning accuracy also - runs along horizontal axis

Don't be put off by Paul's "MAP-Phobic" comments.

Hot wire MAF meters actually "guess" more than MAP sensors as to what the load of the engine is. It assumes that cooling characteristics of the air on the wire is constant. This doesn't allow for changes in ambient air pressure or humidity. Fouling of the hot wire by oil is also common and affects the performance. There is also no reference to the actual boost that the engine is seeing and therefore no compensation for this. Finally there is a significant lag in time between what the MAF meter reads and what the engine is actually receiving. This is made worse by larger intercoolers and duct volumes.

MAP sensors read usually at the inlet manifold and give faster response to what the engine is actually seeing. Load is determined by a combination of manifold air pressure, manifold air temperature and engine revs (with throttle position referenced where there is low manifold pressure i.e. off boost). When constant boost conditions are reached, load is assumed to be directly proportional to engine revs (doesn't neccesarily run parallel to the x axis, but is proportional to it). If you have a look at a log of a MAF meter equipped car, this is also pretty much the same case.

D-Jetro PFC's are a good all round ECU for RB engines and offer great response and performance gains whilst still providing good daily drivability.

[Guilt-Toy]

what paul was saying is that it cannot be done!

If you get the HKS converter i think it can be done. but appart from that....

I like the AFM as well but i am starting to get sick of it getting wet and cutting out all the time... even though if i am hitting boost in the wet i am going to be going sideways regardless what gear i am in and it has saved my ass a few times from getting in trouble,, thats why i have kept it the way it is.

[h2k]

Allright I forgot about the air temp sensor the MAP sensor requires.

Forget about buying a new PowerFC, ofcourse I know one sollution is "just buy a new" ecu. I could also sell my skyline and buy new car if I want more power. But it costs money. The whole point of this topic is exploring options to convert a regular PowerFC from MAF to MAP, and as cheap as possible.

What I want is a small box with 2 inputs and 1 output:

In:

Map sensor

Air temp sensor

Out:

0-5v MAF signal

Ofcourse this small box requires a cpu of some sort to calculate out the final signal to represent air load.

So far the alternatives that have been suggested is:

HKS Vein Pressure Converter

MAF Translator Pro

Both these products does what I need, but it also does alot more I don't need. Wich makes them expensive. The HKS VPC costs the same as a used and complete PowerFC on ebay. And they also offers alot of tuning options similar to AFC units. I don't need it since I have the PFC and it's fuel map for tuning.

There must be somebody who has thought about this and actually done something?

And Im shit tired of hearing: just buy a PFC D-jethro. I want to modify what I have.

[89CAL]

isnt it near impossible to find a djetro for a R33 gtst these days anyway?

interesting thread, if someone could figure it out and put something into production im sure it would be very popular amongst PFC owners

[paulr33]

is your issue that you are hitting 5v or running out of load axis on the PFC

[Adriano]

If it is on an rb25, then you can sell the PFC for more than you can buy an rb26 D-jetro PFC. Send it to URAS, he can make the internal mods to run the rb26 ecu on a 25, although you do lose the VCT which can be controlled seperately. BUT the question is why? I have an AFM that will hit 5v at approx 500RWKW, and wont cause a restriction at that power level, and cost almost nothing to make.

[h2k]

is your issue that you are hitting 5v or running out of load axis on the PFC

both.

I allready put the Q45 internals into a 4" pipe and remapped. Problem is with such a large MAF im having trouble with idling and driving in the city. It's to rough and the signal also fluctuates because of fanblade turbulense. I have a rather large Garrett GT4088R turbo with 4" inlet and not to much space for inlet piping. Also using a atmospheric dump valve, im having a very hard time driving around without stalling the engine. But high speed driving it's no problem with a large maf. Dragracing and trackdays go very well.

But still, this is a topic I am very interested in.

pV = mRT

I've talked to a company(SplitSec) that makes alot of MAF and piggyback fuel products and I qoute them:

"Deriving MAF from pressure is very difficult. The VPC never worked well

which is why HKS obsoleted it. If you want to go map based, which you

should anyway with a big turbo, you need an ECU that can work directly off

of a map sensor"

I agree it might be difficult, but when a d-jethro can do it, im sure another unit also can and convert the output to 0-5v.

[h2k]

If it is on an rb25, then you can sell the PFC for more than you can buy an rb26 D-jetro PFC. Send it to URAS, he can make the internal mods to run the rb26 ecu on a 25, although you do lose the VCT which can be controlled seperately. BUT the question is why? I have an AFM that will hit 5v at approx 500RWKW, and wont cause a restriction at that power level, and cost almost nothing to make.

I've made a 4" maf from a Q45. I still max it out with 5.2v at 5000rpm when running 2.0Bar of boost. I run a rb25det with approx 800ps at the flywheel, reving up to 8000rpm. I want to try map =)

Stop entering negative posts like "upgrade MAF, change MAF, buy d-jethro". I know I can, but I don't want to. I want to trick a PFC to use MAP.

[DaGr81]

they arent being negative, just trying to help mate, chill out

try it out

tell us if it works

[R31Nismoid]

both.

I allready put the Q45 internals into a 4" pipe and remapped. Problem is with such a large MAF im having trouble with idling and driving in the city. It's to rough and the signal also fluctuates because of fanblade turbulense. I have a rather large Garrett GT4088R turbo with 4" inlet and not to much space for inlet piping. Also using a atmospheric dump valve

You've answered your own problem in a way.

Put e decent plumb-back BOV setup on (GTR is fine), and move the AFM further away, even before the throttle body end if you must.

Will fix all your issues for a couple hundred $$

[Guilt-Toy]

don't take us the wrong way... if you come up with a solution then I would be one of many who will sign up for it

I've made a 4" maf from a Q45. I still max it out with 5.2v at 5000rpm when running 2.0Bar of boost. I run a rb25det with approx 800ps at the flywheel, reving up to 8000rpm. I want to try map =)

Stop entering negative posts like "upgrade MAF, change MAF, buy d-jethro". I know I can, but I don't want to. I want to trick a PFC to use MAP.

[discopotato03]

I would not say it's impossible but I can't see how a temperature and a pressure signal can be intergrated to tell an ECU how to regulate fueling and timing control .

I AM biased because I KNOW manifold pressure is not a good indication of engine load . Airflow by mass (weight of air as in lbs or kg /min if you like) is hard to beat for an accurate indication of whats going down the spout . If you can KNOW the mass of the air going in you can accurately regulate the mass of the fuel going in and therefore expect get the desired AFR .

Using an externally venting throttle bypass valve was a huge mistake with an upstream MAF sensed system , obviously when the "BOV" vented the MAF was indicating airflow that the engine was not getting - this is not something the ECU or MAF sensor can be faulted on . It would be a bit like plumbing a MAP sensor into something other than the engine side of the throttle/s and claiming the MAP/ECU was not suitable .

I know it's off topic but are you running a GT4088R on an RB25DET with that engines head/inlet system/valve train ?

A .

[rob82]

The beauy of speed density systems on factory ecu's is that their model for charge temp (the actual air temp of the air in the engine) is mapped over g/s of airflow (which without a map sensor is based on rpm and MAP itself).

If I was you I would rescale the maf down to a suitable size to get good airflow figures from it. I would also place a intake air temp sensor into the manifold. I would then get a micro with at least four ADC. Three input chanels for MAF, MAP and IAT and one ouput for a psuedo MAF votlage for the PFC. YOu then will need to be able to map/tune the intake air temp sensor over MAF voltage as a multiplier of AIRtemp to give you a final Charge temp.

ie

MAF Voltage Air Temp Multiplier

0 2

0.5 2

1 1.9

1.5 1.7

2 1.5

2.5 1.3

3 1.1

3.5 1

4 1

4.5 1

5 1

The actual charge temp of the air in the engine is the "Air temp multiplier" times the current IAT sensor reading. The above mulitplier curve will need to be tuned based on the position of the IAT sensor. You will also need a multiplier of RPM as well to take into consideration the difference in voltage of a linear MAP sensor vs an expotential MAF sensor. I would then apply the ideal gas law and see what happens.

My advice is that unless you have a good understanding of microprocessor design and implimentation and a good tuning back groudround then DO NOT DO IT!!

[Rezlo]

If it is on an rb25, then you can sell the PFC for more than you can buy an rb26 D-jetro PFC. Send it to URAS, he can make the internal mods to run the rb26 ecu on a 25, although you do lose the VCT which can be controlled seperately.

Or you could take 5 minutes looking at the all 3 wires to change in the wiring diagrams and do it yourself, nothing inside needs to be changed. MSD timing window for $80 will run the vct at any rpm point your heart desires at a touch of a button.

H2K, you still have that link of the system i showed you that can convert the signals? cant for the life of me remember its name? Bit pricey but looked very good

[paulr33]

just rescale the AFM To get some more load points to play with and deal with the AFM maxing at 5 grand

it will be the same as your map sensor setup anyway

at 5 grand youll be well into your target boost so boost wont increase, so map PIM voltage wont increase, so your load axis wont increase

both give you the same result

get a Z32 and just baby it up as much as you can, relocate the MAF itself in a 3" shell before the throttle body / after intercooler