Karman Hz cutoffs of stock MAF (LONG TECH)

[PsynceFact]

I am an electronics tech for the FAA with a background in microcontroller programming. I was considering a swap of the stock MAF to MAP, but balk at an $800.00 price tag for a VPC. I have been doing research on the Karman Vortex systems and the MAP systems, and think that I can make a fairly simple MAF to MAP convertor so your ECU/AFC sees what appears to be a stock MAF where in fact there is a MAP sensor/Intake Air Temp/Baro Pressure setup. Benefits? Unlimited flow, no fuel cut, and it reacts like a wider-band MAF putting out Karman-equivalent frequency data. Should be a LOT cheaper than the VPC, and easier to implement. Most people considering this I assume would already have an AFC/S-AFC or similar a/f computer. Can anyone think of stumbling blocks that I haven't considered? Also, anyone in high altitude with a stock or semi-stock MAF and a datalogger? What are your lower/upper Karman Hz readings? What are your intake/exhaust mods?
Thanks

[V8SpankR]

I don't have a datalogger but on my AFC my Karmen readings under full throttle are just over 2100hz. (I only have fuel cut when the outside temp is under 20*F and only above 6000rpm) The only mods on the maf are the lower honeycomb removal and the screw backed out flush. My exhaust system consists of a 2g manifold,small 16g,2.5 inch dp,race pipe and a HKS catback.
I live here in Denver which is at 5200ft and the track I race at is at 5800ft. Hopefully this will help a little.

[RabidDonkeyBoy]

Originally posted by PsynceFact
I am an electronics tech for the FAA with a background in microcontroller programming. I was considering a swap of the stock MAF to MAP, but balk at an $800.00 price tag for a VPC. I have been doing research on the Karman Vortex systems and the MAP systems, and think that I can make a fairly simple MAF to MAP convertor so your ECU/AFC sees what appears to be a stock MAF where in fact there is a MAP sensor/Intake Air Temp/Baro Pressure setup. Benefits? Unlimited flow, no fuel cut, and it reacts like a wider-band MAF putting out Karman-equivalent frequency data. Should be a LOT cheaper than the VPC, and easier to implement. Most people considering this I assume would already have an AFC/S-AFC or similar a/f computer. Can anyone think of stumbling blocks that I haven't considered? Also, anyone in high altitude with a stock or semi-stock MAF and a datalogger? What are your lower/upper Karman Hz readings? What are your intake/exhaust mods?
Thanks


if you could do this with the chrysler 3 bar map sensor that would be the best(factory performance part for turbo mopars). don't map sensors just read out voltage (speculating) 0v-12v, if you could come up with some good circuitry to convert that voltage to a karman hz signal and maybe a dial or some preset switches to modify how much of a conversion rate there is would be great also, granted we'd still have to tune with an safc for the best bennefits.

i'd spend the money on the cost of a 3bar mapsensor ($100?) and the price of your custom circuitry(100 a few unexploded engines 200-250 tested well, hell maybe more) if it means i don't have that stupid maf sensor in the way, can run a better inlet pipe and huge filter at the old ic duct, can choose to vent or not at will and not have any idle problems, i think you'd be greatly appreciated by us and would get quite a bit of business. hks vpc may be well tested & proven, but $800+ no thanks. i'm a cheap bastard.

[PsynceFact]

Thanks for the help. You covered all of my primary reasons for considering this in a nutshell. Talk about cheap bastard...I picked up my 93 TSI for 1500 bucks because it was running like shi@. Took it home and found the guy's idea of a MAF mod was to remove the BIG honeycomb. Since it ran rich as hell, he then disconnected the manifold-to-fuel-pressure solenoid and plugged it (forcing a LEAN condition due to no fuel regulation...always at 1 atmosphere). Being a cheap bastard, I bought a 69 cent box of DRINKING STRAWS, cut them to 1" long, and super-glued them together into a "honeycomb". Just air-straighteners! Hit it with some black spray-paint to cover the stripes, stuck it in (hot glued it in), and the car now idles like a champ. BTW, I did put a screen on the MAF exit side to catch any of the straws that felt like liberating themselves into the turbo. Savings: the cost of a new MAF for 30 minutes work.

This is the >>other<< reason for a MAP upgrade !

[V8SpankR]

Originally posted by PsynceFact
Thanks for the help. You covered all of my primary reasons for considering this in a nutshell. Talk about cheap bastard...I picked up my 93 TSI for 1500 bucks because it was running like shi@. Took it home and found the guy's idea of a MAF mod was to remove the BIG honeycomb. Since it ran rich as hell, he then disconnected the manifold-to-fuel-pressure solenoid and plugged it (forcing a LEAN condition due to no fuel regulation...always at 1 atmosphere). Being a cheap bastard, I bought a 69 cent box of DRINKING STRAWS, cut them to 1" long, and super-glued them together into a "honeycomb". Just air-straighteners! Hit it with some black spray-paint to cover the stripes, stuck it in (hot glued it in), and the car now idles like a champ. BTW, I did put a screen on the MAF exit side to catch any of the straws that felt like liberating themselves into the turbo. Savings: the cost of a new MAF for 30 minutes work.

This is the >>other<< reason for a MAP upgrade !

A regular Macguyver. hehe:D Good idea though.

[FastGSXauto]

i've been thinking about this myself actually. Keep the temp and baro sensors stock so the ecu can compensate, but figure out how much pressure would equate the same amount of air flow at the same temperatures and altitude. Shouldnt' be too hard to figure out the conversion, it's the circuitry that converts 0-5 V to a frequency that would be challenging. But it shouldnt' be that hard, being an ECE major. Any other obstacles anyone sees? One could be the temp after the intercooler would be different than at the filter, but if we take temp after, it would be more accurate when the ecu calcuates mass anyways.

[Taboo]

I've been wondering if relocating the temp sensor (and/or other sensors) as close to the throttle body as possible would result in some benefits as well (giving the ECU more accurate info).

[GSTSpyder]

Psynce, I have been thinking the exact same thing! I used to work as an embedded systems engineer, I did mostly programming for the PIC microcontroller (and the UNIX interfacing) but I have some friends who are skilled in chips like the AVR and Rabbit, I think that any of these would be a good candidate to convert the MAP->MAS Karman frequency count.

My email is jon@powerful.org, feel free to drop me a line if you feel like working out the technical correspondence...

GSTSpyder

[FastGSXauto]

Does anyone know the amplitude of MAF's output? It varies the frequency based on airflow, but the amplitude should stay the same. I'm guess it's probably 0-5V, but does anyone know?

[Rogue_Ant]

The way I understand Speed Density systems (i.e. MAF) is they take a couple of variables to include Manifold Pressure to get an 'airflow' #.

This won't be as easy as just converting your Map's Voltage (0-5v) sig into a Maf type Hz.
You will need to know engine manifold pressure, engine rpm and prob throttle pos to derrive with a 'Hz' number.

Rogue

[captain4g63]

Originally posted by FastGSXauto
Does anyone know the amplitude of MAF's output? It varies the frequency based on airflow, but the amplitude should stay the same. I'm guess it's probably 0-5V, but does anyone know?

It's a 5v square wave. The frequency is generated by incomming air hitting a piece of foil. An LED shines on the foil as the air shakes it; a photo diode pickes up the light, or doesn't, generating a square wave.

[FastGSXauto]

is it a 0-5V square, or -5 to 5 square?

[Tondar]

please keep in mind that speed density systems have to be recalibrated any time you change the breathing characteristics of the engine. Not that big of a deal but something to consider..

[captain4g63]

It's a logic-generated signal; it's a 0-5v square wave

Captain