Baro compensation is locked in most products as its not required for hot wire impementations as its output is already compensated. IAT from the ford sensor is very close to the IAT output of the stock MAF.. Been using this sort of setup since 2003 with very good results (600whp on a stock ECU kind of results) It makes tuning a little different though, as you no longer can use the ECU's built in BARO compensation, so you have to make allowances for variations in the MAF Frequency in your open loop fuel tables. However this has had no noticable impact in drivability and tuning isn't all that different if you don't have large air pressure differences (altitude change is the only thing that effects it by very much anyway) that can shift the tune.

do a search for a thread started by me, with the search terms "Blowthrough MAF" or "Blow Through MAF"

The technology never really caught on with the Evo market simply because Evo owners were just intent on running an AEM and Speed Density, instead of keeping it legal.

BTW IAT is actually an easier sensor to replace because most manufacturers use the same basic thermocouple (most even use the same manufacturer of the sensor)

 

But I see no reason to go through all that trouble when you can just forget about the EVOX sensor, and reprogram an existing high capacity aftermarket sensor that reports in Hz to match the factory EVO 8-9 sensor (which also reports in Hz). No outboard 'box', no messy ECU reprogramming.

We discussed that and resolved that the IAT reading is important for MAF accuracy.


This indicates that 2/3 of the problem already has a solution.

- A PMAS MAF can be recalibrated to match the Mitsu MAF transfer function
- The Ford IAT is close to the Mitsu IAT

The only remaining piece of the puzzle that would be nice to resolve is to take the BARO from an appropriate outboard sensor. That would make the system 'air tight'.

As far as suitable MAFs, this one would be a snap:
http://www.massairsystems.com/VELOCITY.htm

It has a 4" outlet (same size as large turbo inlet), and since it is mounted to its own air filter, only one standard recalibration is required for all draw-through refits.

Those who are intent on making a blow through setup work would use this:
http://www.massairsystems.com/HPX.htm

 

PMAS has promised several times to provide me with information and the ability to purchase hardware which is supposed to have the transfer function embedded in the sensor (should be programmable, but even if it was programmed by them, for a stock EVO curve I'd be fine with it) however they have only told me what they can do, and never followed up with any real hardware other than them being "out of stock" or "in development" This has been 2 years of waiting for me.

In other words, For as much as I'd like to endorse them, I cannot and will not, until they can provide me with the hardware that will adequately replace my earlier proflow setup.

The only useful info I have ever gotten was from Antilag2000 but any time I contacted PMAS they basically blew me off.

 

Oh and the Baro sensor may not ever be required, as its used by a Karmann Vortex calculations to correctly baseline the air pressure so the airflow measurements can be converted to Mass. this isn't necessary with hot wire as the voltage output is the cooling effect of air blown through the sensor, which is already basically compensated air mass.

If you want to use the Baro compensation tables in the ECU, then thats a different story, but that usually is what makes adjustments to the basic MAF output before mapping to the fuel table.. The resulting output in either case ends up nearly the same. My earlier statement applies though, as the baro table is used to accomodate large altitude changes, which doesn't apply to most people after they have a base tune.

Large air temp changes have the biggest effect, and the IAT sensor can already be handled.

The end result is adding a Baro sensor "Might" double compensate.

 

I thought about this a bit on my way home from work and I think Bez's speed density code would work for this. The MAP-MAF table if I understood it correctly is simply a table that converts a 0-5V signal into a MAF frequency (or potentially airflow rate?). While Bez meant for a pressure transducer to be used, a 0-5V MAF sensor could be used instead and the table would just need to be setup accordingly.

The VE table could be eliminated, as could the IAT table he has added because neither of them would be needed since direct measurment of the airflow is being done.

I think I was misunderstood about the IAT stuff though. the way I see it, the ECU has 2 tables for IAT correction. The first table is used for density correction, this is the table that is linear and varies from like 0.85 to 1.28 and matches the ideal gas law. This table in my mind is likely used as a multiplier on the MAF frequency and is used to calculate mass flow rate from the air velocity measured in the factory "MAF." The only purpose of this table is to correct for density since the factory "MAF" is actually a velocity meter and not a mass airflow meter.

The second table is an IAT trim map. This is where tuning for different ambient conditions is done. Changes to this table would allow you to lean out the miture under ambient temperatures where the setup is more tolerant and can be leaned out without detonation.

What I am suggesting is to zero out the first table, because a hot wire MAF already accounts for density correction. The second map would still be used to provide IAT trims.

As for Baro correction, I think it is worth mentioning again that the EVO X uses a baro sensor inside the ECU along with the hotwire MAF. I think this is important to realize and I wouldn't be surprised if the GM and Ford systems did the exact same thing, despite everybody just assuming baro correction is not important for a hot wire MAF.

 

Speed density is NOT a good idea.. Its like taking a step back to having a carburetor. Speed density is good for making tuning easier, but it does not do a good job of compensating for changes you would experience in daily driving. Don't get sucked into that whole brainlock.

(Sorry misread your post, you wanted to use the speed density code to create a MAFv-Hz transfer function)

I have a huge issue with making this modification in the ECU directly. I have driven my car since 2003, the one thing I have discovered is driving is unpredictable, and on more than one occasion, I have needed to go to a dealer to find a replacement part in an emergency. I have gone out of my way to make sure that regardless of my modifications, I could swap in a stock component in an emergency (I keep a stock MAF on a Dejontool intake tube in my trunk, that can be swapped over in a few minutes) Keep in mind in my case I have to still swap maps, but I could at least get the car running and moving.

 

Again, why go through this exercise when a high capacity aftermarket MAF that reports in Hz can be easily recalibrated by its vendor to match the factory MAF transfer function (also a function of Hz)? I don't see the advantage.

Ok, but somewhere in there are VE correction tables that determine theoretical VE with respect to conditions that alter air density, such as IAT and BARO. When ambient temps rise and/or we go to altitude, the air mass indicated for any given VE decreases. We don't want to fiddle with those.

A hot wire MAF maintains a wire temp of 100C above ambient, and depends upon an IAT sensor (internal or external) to do this. Maintaining a wire temp that is always fixed with respect to ambient temp makes the actual air temp a constant instead of a variable. So long as the wire temp is 100C above incoming air temp, the meter is accurate.

The accuracy of a hot wire MAF shouldn't be affected by air density, because it senses air density with respect to volume. As I mentioned previously, the BARO gives the ECU a baseline of sorts so the ECU can determine exactly what constitutes a given VE considering ambient atmospheric conditions.

 

Why not?
I understand that's not what you want. However, I'd personally be more interested in a $100 hot wire MAF and some ECU reprogramming then a $400 custom MAF. To each thier own, but I don't agree with your mind set on this, particularly when some of these sensors have already been proven to work just fine at high HP levels.


I'm talking about a VE table and IAT table that Bez added to the factory ECU to implement speed density. We don't need these additional maps because the ECU already has adequate tables for IAT compensation and VE correction is irrelevant in a MAF based system because you directly measure mass flow rate. I suggest removing them for this simply to reduce the amount of unused maps/calculations in the ECU.



I think we are on two different pages here. I'm talking about the factory ECU uses IAT as a compensation in the airflow calculations. You seem to be talking about how a hot wire MAF works. In the end, it doesn't really matter how it works provided the signal output of the MAF sensor is a voltage output that is proportional to mass airflow rate. If the hot wire MAF accurately accounts for air temperature changes, then all we need to know is that we don't want the ECU double compensating for it, thus the reason for setting the IAT table that is used in the airflow calculations to unity.



I'm not implying that baro affects the accuracy of the MAF. I'm actually implying that most of these systems likely maintain baro correction despite the hot wire MAF automatically compensating for changes in barometric conditions.

 

I don't know how possible it would be, but something like an "if-then-else" statement might be usable to meet your needs. Would it be possible for the ECU to look for connection of a factory MAF? If it sees a factory MAF connected, use the factory MAF, if not, use the 0-5V input?

 

Because the scenario I suggested is already proven to work (see antilag-200's post). I'm right about where Mellon is in the scheme of things. If I can get into a 4" MAF that can be dropped in, without adding another layer of custom ECU calculations, for $3XX, I'd take it. If I were as convinced by Bez' setup, I (and a lot of others) would already be running it. There are thousands of ways to make things more complicated. The simpler, the better, and simplicity has value IMO.


It does, so long as it has a constant IAT signal, and so long as that IAT signal is used to maintain proper function of the meter.

They do because as I said, changes in ambient air pressure affect theoretical VE. The BARO compensates for this, and it is useful where changes in altitude are expected (which othewise throws off the tune). If this can be retained, it would be advantageous.

 

I agree, I think Bez's setup could be fine tuned. I'd also prefer a frequency based system simply because frequency is a lot more robust against noise.

I'm just looking for various options in ways to improve the tuning capabilities. I suggest the hot wire MAF like what is used in the IX because it actually opens up possibilities for different installation.

Call me a ricer, but I prefer to run a TIAL BOV because I like the sound and I know it will hold any boost I ever care to hold while supporting enough airflow to keep up with something like a GT42. I'd love to drop in a nice little compact hot wire MAF post BOV in a 3" IC pipe and not have drivability issues. When the sensors like the EVO IX and Subaru STI sensor have been proven to be capable of this, it has me very interested in implementing it.

I wish I had more time to mess around with my car, because I'm very tempted to just grab a Subaru sensor from a friend, toss it in and use BEZ's patch to give it a shot.

 

We definitely need to resolve what PMAS can do and what they cannot do with respect to Pro-Flow's prior capabilities.

 

But for those of us with no current interest in an aftermarket turbo w/ 4" inlet or a $300 part... a blowthrough setup with a cheap sensor would be great. I wouldn't want this modification because I'm running stupid amounts of power as much as I'd just like a blowthrough setup that isn't going to crap out on me if an IC pipe blows off on track or my DV leaks. The GM in blowthrough was great for that... but I had to sacrifice tune reliability and repeatability. Plus it was quirky.
Heck, there's already the modification to log manifold air temp via GM AIT.

 

Right, but antilag_200's setup above is almost exactly that. It may cost $3XX, but it comes matched to the factory MAFs response curve, and is a drop in item. It's rated for 1000+hp, so it is capable. Since antilag_200's 'tuner box' seems to be something that simply allows tweaking of the transfer function, we already have the ability to do that in the existing XML for all ROMs (which should eliminate the need for the box). It may be that the transfer function only need be tweaked for a blowthrough setup anyway.

We need to confirm that antilag_200's setup maintains proper IAT function to keep the MAF accurate.

If we can figure a way to use a regular BAP sensor to deliver an appropriate BARO signal, that would be the icing on the cake.

 

I agree with this. I think in the end we all want the same thing but there are many solutions to the problem. Personally I don't mind paying for something that works, within reason. If i could pay sub $400 for a solution that was close to PnP I would do it. It is the same reason i paid $130 for a 3-bar map sensor instead of $50 for a GM, it dropped into a stock location and just works with minimal effort.