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Thread: Tuning Blow Through MAF
07-15-2019, 09:47 PM #1
Tuning Blow Through MAF
Tuning my Bullitt using SCT PRP. I installed a SCT BA5000 MAF in a blow through configuration with a Vortech SC. Do I need to scale the MAF Transfer function for boost? Or will the MAF Transfer Function provided by SCT work as a good starting point?
07-16-2019, 01:08 PM #2
The MAF xfer function has a hard stop that Ford puts into their ECUs. That hard stop is 63.9 pounds of air per minute or 1739 Kg/hr. If your MAF flows more air than that (which it almost certainly does) then you will need to begin scaling various parameters within the ECU. It would be to your advantage to visit Don LaSota's website and buy his book for the year car you have and the tuning software you choose to use.
If you have not bought the SCT PRP package already you might want to consider a different provider. If you have bought PRP and it is a year or more old do not update it from their site or you will end up with a new neutered version of the s/w designed to meet the tuning limitations they have recently agreed to abide by (at your expense) in their consent decree with EPA. Consent decree issues not withstanding, you can pick virtually any other provider of tuning software and the worst one you pick will have better customer service than SCT — something to think about ...
If you are planning to build a high performance supercharged engine with the Ford OEM ECU you ought to take a step back and give serious consideration to a stand alone. The Ford ECU runs out of adequate CPU processing power to reliably operate above 7,000 rpm. Additionally the OEM ECU is only capable of firing dumb ignition coils. Most of the dumb ignition coils are only capable of providing around 20 millijoules of spark energy. That becomes either marginal or insufficient around 6500 rpm and you will begin to experience spark blowout with attendant reductions in power. Additionally there are no safety shut downs for high temperature, low oil pressure, low fuel pressure etc. Important to have capabilities (for supercharged engines) like knock detection / suppression logic is missing. Of course all this is not surprising because those ECU's were intended for grocery getters purchased at your local Ford dealer.
Many of the aftermarket ECU's will not support your instrument panel and other OEM features, which means you either have to give up your instrument panel or run the aftermarket ECU piggy back on top of the OEM ECU with the aftermarket ECU handling just the engine management. In the next 30/60 days DIYAutotune (<= clickable) will begin to offer a Ford specific version of their MS3Pro Ultimate engine management system that will come with an OEM compatible connector to plug into your OEM harness. It will run your engine and the instruments et al. The MS3Pro Ultimate doesn't require scaling, uses your stock sensors, supports the high output (108 millijoules) Mercury IGN1-A racing coils (if you want to use them), provides multiple engine safety routines to shut down the engine and prevent unnecessary damage, provides a very nice tunable knock detection and suppression capability, has an even more impressive OEM style traction control capability and has no problems with engine speeds over 10,000 rpm — which you likely won't go to.
Might be worth the wait time ...
Last edited by eschaider; 07-17-2019 at 04:53 PM. Reason: Spelling & Grammar
07-17-2019, 11:44 AM #3
Thanks Ed. I may consider a stand alone ECU if I boost above 1 bar (15psi). I currently use SCT PRP and I'm confortable with it. The SCT PRP will support engine loads up to 1.9 so it works good for boost of 15psi or less. Over that and you have to start scaling.
I tried the Moates Quarterhorse and switched back to PRP because of ease of use and datalogging capability.
DIYAutotune is an awesome website, lot's of good tuning information there.
BTW, someone pointed out to me that the MAF measures AIRMASS not AIRFLOW, therefore X amount of airflow at 1 bar will be half as much as x airflow at 2 bar. The MAF XFER will be accurate drawthrough or blowthrough.
07-17-2019, 04:47 PM #4
The scaling of the ECU parameters is solely due to large MAFs and large injectors that exceed the hard stops Ford has programmed into their strategies for those components. In the case of a MAF, that Ford imposed hard stop is 63.9 lbs of air per minute or in metric terms on an hourly time base 1,739Kg per hour. If your MAF outperforms these hard coded thresholds Ford has placed into their code, then you will need to begin scaling various parts of the tune. The LaSota book can be a very helpful reference document for you if you need to do this.
Something you may not be aware of is that, the Quarterhorse logs data either 10 times or 100 faster (I've forgotten which anymore) than the SCT PRP package and provides substantially more variables that you can data log simultaneously at a higher frequency than the SCT PRP software. There also is a wireless bluetooth data logging capability available so the event can occur w/o the usual cabeling and of course there is no hand held data logging device to buy like SCT requires, either for data logging or for loading a tune. Data logging and tune uploads can be done directly from your laptop.
Whoever told you that, Scott informed you correctly but not completely. MAF's do not measure air flow although that can be calculated from the Mass Flow or vice versa. MAF's measure air mass passed to the engine for combustion. The weight component of air consumed is the measure of the mass of air that the MAF will pass. The time component is the time base over which period of time that mass of air has passed through the MAF. That composite metric is communicated back to the ECU as a two dimensional variable used (in conjunction with injector sizing, fuel rail delta pressure and engine load) to calculate injector pulse widths necessary to deliver the AFR commanded in the the tune.
The calculation of air mass is more complex than Air flow times BAR. If you remember the Gas Laws from your High School Chemistry classes, the three laws that impact air mass are Charles Law, Boyles Law and Avagadro's Law which collectively were distilled (along with some others) into The Ideal Gas Law.
The Ideal Gas Law, as you probably recall, is frequently represented as PV=nRT.Where P is pressure, V is volume, n is the amount of gas measured in moles, R is the Universal Gas Constant and T is the absolute temperature in K˚. One mole of any gas at STP will contain constant number of molecules of that gas in a volume equal to 22.4L at Standard Temperature and Pressure (STP). That number of molecules is called Avagadro's number or 6.023 x 1023. Knowing the molar weight of the gas we can compute the mass of any given volume of that gas given the pressure, temperature and volume occupied by the gas. Once we know the mass per unit volume and the volume of air being consumed we know the weight of air consumed.
An alternate, although similarly rigorous methodology to the density and then later the mass calculation relies on,
𝝆 = mass density (kg/m3)
Tb = standard temperature (°K)
L = standard temperature lapse rate (°K/m) in ISA
h = height above sea level (geopotential meters)
R˚ = universal gas constant 8.3144598 N·m/(mol·°K)
go = gravitational acceleration: 9.80665 m/s2
M = molar mass of Earth's air: 0.0289644 kg/mol
Irrespective of which methodology you pursue, the the air mass calculation model of airflow @ "X" bar pressure will not yield the correct air mass. Air mass calculations are much more sophisticated.
Last edited by eschaider; 07-17-2019 at 06:22 PM. Reason: Spelling & Grammar