Voltage divider for MAF

[Blackcoog]

Anyone wired up a voltage divider on their MAF instead of swapping to a different Ford MAF? The MAF housing itself is not restrictive so it seems odd that all the FI people switch to a huge 80 or 90mm MAF. Everyone must run a huge step before and after the MAF to get it to fit which can't be good for sampling the air flow. Wouldn't running a voltage divider on the stock MAF be a better option or do you loose resolution?

Using the SCT Pro Racer package you could just scale all the values based on the voltage divider you pick. For example I'm pegging my MAF at about 5700rpms. If I were to run the output into a 1k Ohm and then a 4k Ohm. Ground the other side of the 4k and pull our new output from between the resistors that would change 5v to 4v on the output which should give me more than enough range. I can multiply my transfer function by .8 and I should be set right?

edit: Looks like I'm going to try the voltage divider. A guy here at work has a 600whp 98 Cobra that he did this to. Works great for him. He also has the SCT Pro Racer package. I can't figure out why all the mustang guys drop $150 on a MAFIA to extend the MAF range when it's really just a POT with connectors on it in a nice case. You'd think they'd know that they can save $149 and build their own that will work just as well.

Chris

 

[gorman]

Wouldn't running a voltage divider on the stock MAF be a better option or do you loose resolution? Chris

i haven't seen the PRP. If you could increase the table so that it had more value reference points...... then you would get your resolution back.....wouldn't you ? ...G.

 

[TRicker]

i can't agree with you guys here. if you have a problem with a maf reading you just need to up the size of the tube to allow enough air in before you peg the max flow of the maf. thats why they go with a bigger housing. it might not be the best way, but neither is using a stock maf housing. at 325 whp you can't tell me your not close to the max flow potential of that housing.

just keep in mind that different styles of maf will give you different air samples too.

my pro flow housing has a small tube in it that tapers slowly downward to the sensor to "accelerate" the airflow. i imagine this would be worse for your setup. a bigger maf with a center shaft with the "offset plate" on the back side to slow down the airflow through the sensor is probably better and will allow you to get the flow you need to the engine without pegging your maf flow voltage.

of course for the finest tuning the way i would go is probably avoiding the issue and i'm sure when i do finally boost my car i will change my mind. currently i run a 75mm maf housing with no center shaft (factory ford) just two wires into the open housing. This would probably be way too hard to tune for boost though


anyways my point is i think that the voltage range of the maf isnt as important as the airflow vs the reading capabilities of the sensor itself in the housing.

 

[gorman]

i can't agree with you guys here. if you have a problem with a maf reading you just need to up the size of the tube to allow enough air in before you peg the max flow of the maf. thats why they go with a bigger housing. it might not be the best way, but neither is using a stock maf housing. at 325 whp you can't tell me your not close to the max flow potential of that housing.

Maybe you can pump far more air through it, than you can efficiently suck air through it ?? .... G.

 

[warmonger]

You mean like an SAFC, MAFia, eManage, etc.?

Yes. But it ruins the sampling anyway on large applications. The problem isn't rescaling the voltage from the MAF as you can see with the above products (same principle as a voltage divider).

 

[TRicker]

no warmonger, chris runs the XCAL pro racer package. what he's saying, is he wants to make his stock maf calibrated for a different voltage range, by putting a resistor in it.

apparently its big with cobra guys, they can tune more accurately with that somehow. i dont see why chris doesnt just run a bigger maf though

 

[warmonger]

Yeah, I think I'm tracking what he wants and I was just trying to point out that the above products do exactly that with a bit of programability.
THe resistor or the products or above methods will not fix the problem of sampling resolution. I'm not sure what will but I suspect it is in the actual maf solid state electronics.

 

[warmonger]

I just noticed what you were trying to ask, sorry I was tired last night.

If you use a voltage divider then the voltage you send to your PCM will never reach the full 5 volt maximum, it will decrease the voltage range to something between 0-4 volts. Now that isn't bad if you can alter the transfer function in the PCM with a racer package but you then have to rely on voltage points that are closer together to get the same 30 points loaded in the pcm. Lets say 100cfm was 2.0v last time, now it is only 1.5v
You have only 1.5v to break up 0-100cfm now. Your maf voltage may only be accurate to +/- 0.1v so there is a point where it will not have the resolution if the voltage divider makes a large impact. A small amount would be fine I'm sure. We generally used to go with a +20%scaling when using the SAFC/eManage to scale the maf voltage. Above that and it just went haywire and wouldn't work well.
I would leave the MAF alone if I had a PRP and I would increase the fuel as necessary using some of the other functions that are available in the program. There is a WOT multiplier that you can use and then you can actually scale back the MAF function in the lower range to compensate for the added multiplier whilst leaving the higher range as is to increase your fuel while maintaining low-end response.
There are more ways but this is a basic idea.


Oh, and the larger MAFs do work fine for low-resolution sampling. The largest problem you are probably aware of is having large transitions or bends right in front of the MAF. Ideally, you will get the best results if you have the filter right on the MAF because the air is uniform, has not developed into laminar flows nor is it accelerating around a corner to the outside of that corner. If it must be in a pipe, have at least 10 inches of straight pipe and use a dispersing screen as was found in the old SVT filter box in front of the MAF. This will work wonders on a car with erratic low-idle readings and smooth the function out even on a 90mm MAF with a 2.5L engine.

Anyone wired up a voltage divider on their MAF instead of swapping to a different Ford MAF? The MAF housing itself is not restrictive so it seems odd that all the FI people switch to a huge 80 or 90mm MAF. Everyone must run a huge step before and after the MAF to get it to fit which can't be good for sampling the air flow. Wouldn't running a voltage divider on the stock MAF be a better option or do you loose resolution?

Using the SCT Pro Racer package you could just scale all the values based on the voltage divider you pick. For example I'm pegging my MAF at about 5700rpms. If I were to run the output into a 1k Ohm and then a 4k Ohm. Ground the other side of the 4k and pull our new output from between the resistors that would change 5v to 4v on the output which should give me more than enough range. I can multiply my transfer function by .8 and I should be set right?

edit: Looks like I'm going to try the voltage divider. A guy here at work has a 600whp 98 Cobra that he did this to. Works great for him. He also has the SCT Pro Racer package. I can't figure out why all the mustang guys drop $150 on a MAFIA to extend the MAF range when it's really just a POT with connectors on it in a nice case. You'd think they'd know that they can save $149 and build their own that will work just as well.

Chris

 

[Blackcoog]

i can't agree with you guys here. if you have a problem with a maf reading you just need to up the size of the tube to allow enough air in before you peg the max flow of the maf. thats why they go with a bigger housing. it might not be the best way, but neither is using a stock maf housing. at 325 whp you can't tell me your not close to the max flow potential of that housing.

The housing will never EVER be the limiting factor for the stock MAF on our cars. The 2.5" piping I'm running off the supercharger has less volume than the MAF. The MAF has the largest volume in the piping up to the intake. It is definitely not a restriction.

Based on my dyno I only need an extra 10% at most past 5V. I understand that there will be a slight resolution loss but it should only be minor and won't be an issue.

 

[warmonger]

Yeah that should be easily done with the method you are looking at.

 

[2000ZxT]

The 2.5" piping I'm running off the supercharger has less volume than the MAF. The MAF has the largest volume in the piping up to the intake. It is definitely not a restriction.

X2

I'm not quite sure why people here go with 90mm maf's their builds, the 4" inlet is ridiculous for a 3.0. I guess it's the same thing with people making hp suitable for an OEM clutch going with horrible street behaving 6 pucks :shrug:

 

[SHOgoFast]

I would say because it is 'easier' to install a larger MAF vs messing with resistors and then having to scale tables with PRP.

.02

I agree that the size is overkill.

 

[Blackcoog]

I would say because it is 'easier' to install a larger MAF vs messing with resistors and then having to scale tables with PRP.

.02

I agree that the size is overkill.

Either way you need to mess with the tune. Scaling the current table would be easier than coming up with a completely new table for the new MAF.

 

[TRicker]

X2

I'm not quite sure why people here go with 90mm maf's their builds, the 4" inlet is ridiculous for a 3.0. I guess it's the same thing with people making hp suitable for an OEM clutch going with horrible street behaving 6 pucks :shrug:

i would say its because i had approx. 210 whp on a stage 3 spec clutch and i shattered it into little bits and pieces. plus my 6 puck is beautifully behaving on the street. it chatters a bit in neutral w/ clutch disengaged though. my only complaint about it thus far.

 

[warmonger]

X2

I'm not quite sure why people here go with 90mm maf's their builds, the 4" inlet is ridiculous for a 3.0. I guess it's the same thing with people making hp suitable for an OEM clutch going with horrible street behaving 6 pucks :shrug:

Well it looks to me like you are willing to hear some counter-opinions so here goes.

People use 90mm because they ARE easily capable of being tuned into a 3.0, they hold all the airflow a maxed out 3L with turbo are capable of moving and more, and they are cheaper than going out and finding a more appropriately sized 80mm from the old cobras and lightnings.

BTW, depends on the 6 puck clutch. I've driven some that were outstanding and not any worse to launch than my MS3 factory clutch.

 

[warmonger]

Either way you need to mess with the tune. Scaling the current table would be easier than coming up with a completely new table for the new MAF.

You don't need come up with a completely new table. You just plug in the transfer function, make small changes based on the trims and command the WOT values where you want them. Let the adaptive learning adjust all the idle and cruise.
FWIW: Placing the MAF correctly as discussed earlier and ensuring no intake/vacuum leaks before beginning to adjust the MAF functions are so far the only reasons for the large MAFs not working properly when first installed.