jsmcortina wrote:I'd more likely use MS3 to give full sequential and trim. Plumb in two MAFs and connect both. Tuning would only use one MAF only but you could datalog the other to see how they compare.
James
Well, I could do the same with my ecu, put the other non used maf on one of the ADC's and log it. If it matches the first one closely then I could just as well use one maf and adjust the gram per second values (if such a thing exists) accordingly.
Is there a code that can be plugged in to read the voltage as gps and log it somehow so that i can see it in mlv ?
elaw wrote:Here's an idea: how about putting two MS mainboards & processors in a single custom case, and sharing relevant signals between the two electrically?
For example for the VR sensor, just connect it to one mainboard, then route the VrOut signal from that mainboard to Tsel on both mainboards.
Likewise for shared analog sensors, connect the sensor to one mainboard, populate the pullup resistor on that mainboard but omit it on the other, then just route the signal to the 2nd mainboard via a wire. For example for CLT, connect the CLT sensor to mainboard #1 and on mainboard #1 populate R7. On mainboard #2, do not populate R7. Then run a wire from the R8/C6 junction on mainboard #1 to the same point on mainboard #2 and both will see the signal from the CLT sensor.
The biggest issue is for engines like the RB26, where each MAF feeds a separate turbo, is that there is little chance that both turbos are drawing the same amount of air, seeing that they are power by separately by the front three or rear three cylinders. Nissan achieves this by assigning half the value for each MAF in the VQ tables (MAF sensor table) and adding them together before it calculates fueling and load, essentially averaging the two. But it seems that if there was an option for two MAF, then twin turbo applications would have more accurate fueling, like some Audis, Nissans, and custom turbo setups (LSx, other V8s). There wouldnt be a need for two separate MAF tables. Just an option to control certain cylinders per MAF, like EGO control or just average the two together, as the RB26 just joins after the turbo anyway.
Nissan Skyline R34 RB26DETT ran MS3/MS3X w/ factory Hitachi CAS (sold)
Nissan Silvia S14 RB25DE ITB/NA ran MS3/MS3X w/ factory Mitsubishi CAS (disassembled)
Datsun 240z RB25DE ITB/NA with MS3/MS3X
There are engines out there (the specifics escape me) where the exhaust from the left bank drives the turbo that feeds the right bank, and vice versa. While this adds a bit to the intake plumbing, this is a self-balancing arrangement that minimizes or eliminates the need for balance valves and other toys.
Temporarily shut down - back soon!
QuadraMAP Sensor Module -- PWM-to-Stepper Controller -- Dual Coil Driver
Coming soon: OctoMAP Sensor Module TTR Ignition Systems
winstonusmc wrote:back in the day, 300zx guys would run a dummy MAF and adjust the tune on the factory ECU to run dual intakes.
Yes, I read about that. I intend on using a dummy maf as well to get the same airflow. However, intake tracts are not totally the same due to space constraints. If the cylinders draw the same amount of air (I balanced them with them being itb's) then I would assume measuring one bank only would yield a pw which drives all injectors and therefor the right bank would be the same...correct.
Fueling tables are usually set to 100% where anything above would be an adder. I could still run VEAL and have the ecu sort out any differences right ?
It would seem that I would have to be extra carefull with the pcv system and the iac. At this moment those are fed into a common vacuum plenum below the manifold that is connected to all cyls with a small hole. However the IAC takes it air from the right box, as well as the PCV system...
maybe a stupid question here
but why are you trying to run 2 mafs? could not get that from your post
you want to be able to tune both injector banks to a different VE value?
do you need to flow more air?
if like you said you need a 112 mm diameter why not build a custom one
insert the maf sensor and tune the maf value voltage curve!
no experience with MAF so just throwing this out there
The reasons are complex :
- itb manifold in crossram form with each cylinder bank fed from the opposite side with an seperate airbox.
- space constraints, that make it difficult to mount a big tube certainly if it has to go over into cold air in front of the radiator (corvette C3)
If there is no other option than to run that setup and MAF has to be used, this got me thinking
winstonusmc wrote:Nissan achieves this by assigning half the value for each MAF in the VQ tables (MAF sensor table) and adding them together before it calculates fuelling and load, essentially averaging the two.
Could this not be imitated by running the two MAF signals to a summing op-amp with k=1/2 to stay in the 0-5V range, thus making sure that the VE table is adapted for the total flow, and take care of the flow differences between the two banks by tuning with dual WB?
Just thinking aloud here... and I'm certainly not an electronic specialist. Is this condemned by some obvious fact I haven't spotted?
Unfortunately there is a problem with that - the output from most voltage-output MAF sensors is not linear. It's usually some variation on an exponential curve. So averaging would give an incorrect result.
Here's a rather extreme example using the MAF sensor that's on my car (whose output in addition to being approximately exponential also has an offset): 2 volts output represents 18 grams/sec flow. 4 volts represents 146 g/s. The average of 2 and 4 volts is 3 volts. 3 volts corresponds to 54 g/s which is not the average of 18 and 146 (the correct result would be 82).
Eric Law
1990 Audi 80 quattro with AAN turbo engine: happily running on MS3+MS3X
2012 Audi A4 quattro, desperately in need of tweaking
Why mess with MAFs at all? MAF sucks. You could easily run speed density or alpha-n on an ITB setup and it would work way better. Or run the ITB mode, granted I haven't looked into that but im assuming its probably a modified alpha-n type fueling.
If you wanted per-bank VE tables you can run the dual fuel, or just use the injector trims with a single VE/Alpha-N/ITB table.
I clearly hadn't spotted that. It's clearly an issue for the extreme case that you are describing, but would it be so bad in the case of a real engine where both mafs should read close values? Any curve can be locally approximated by a straight, where averaging would work. The issue is on the validity zone of the linearization.
Still, this could be refined with a small uc knowing the curve and adding the two resulting values rather than raw voltages, which could communicate with the ms either by can or by outputting a 0-5V signal going to the maf input, but at that point it might well be easier to just add this crude logic to the code, with a choice of secondary adc for the second maf.
Can I assume that the airflow going into one bank and measured by the other bank is representative enough to get a correct pw ?
I have another question : I see in the ms2 v3.57 hardware manual that a protoboard circuit is necessary before the signal from the maf goes to JS4 or JS5. Why is that ? I thought these mafs put out 0-5V so I would think this is directly usuable ?
i was going to mension that
if your intake,s are an exact match just crossing over the engine
airflow and there fore fuel demand would be the same
so you just have to measure 1 intake MAF
