Hi
I am thinking of moving the MAF sensor to after the turbo. Is there anything I should be aware of before I go ahead and do this?
yep, you will need it remapped if you change teh dimensions of teh tube it sits in.
You'll probably have to get the e-Manage re-tuned afterwards, but other than that I can't think of any obvious problems in moving it.
*EDIT* Beaten by 3 seconds!
Hopefully I am keeping the tube dimensions the same.
Agree with whats already been said and assuming you have the OEM MAF sensor and are not using the greddy pressure sensor option.
.
If you do happen to go with a smaller diameter tube say 2.5 inch then you wont be able to run over 10psi because the MAF reading will be higher than with a 3" and you'll risk running off the end of the injector map because the MAF will be effectively "maxed out" at 5volts.
If you go with a much larger, say 4" tube, then the voltage resolution will be reduced damaging idle and fueling accuracy.
But intake dimension should hardly matter with a MAP because then only the AIR map is used to correct for the larger injectors during off-boost operations.
What is the benefit from moving it? Are you relocating the air filter or is the maf just in a cr*p location?
Quote from: "Jap GT300"What is the benefit from moving it? Are you relocating the air filter or is the maf just in a cr*p location?
I assume it's before the turbo now (from the 1st post).
It does measure the air just fine even there, but the temp sensor has no idea what's entering the engine after the turbo and possible IC s:? :? s:?
Quote from: "Tem"Quote from: "Jap GT300"What is the benefit from moving it? Are you relocating the air filter or is the maf just in a cr*p location?
I assume it's before the turbo now (from the 1st post).
It does measure the air just fine even there, but the temp sensor has no idea what's entering the engine after the turbo and possible IC s:? :? s:?
Yep, what TEM said.
1.
Better Tuning due to getting accurate intake tempuratues which affects timing and will allow for a more powerfull and stable tune.
2.
Better reliability because any air leak in the pre-turbo setup between the MAF and the TB will cause poor idle,no start, rough running.Moving it post I/C means the I/C could fall off and the car would run fine just no boost.
3.
Better maintenance - Maf and air filter easier to get to and clean.Air filter not threatening to popoff with each shift or rub a hole in the CV boot.
what else?
Quote from: "MR-S Turbo"Hi
I am thinking of moving the MAF sensor to after the turbo. Is there anything I should be aware of before I go ahead and do this?
Yes - very bad idea.
MAF reads airflow, not quantity. Moving post turbo means you'd really need a full ECU not a piggyback - when the MAF is pre-turbo it reads full amount of air going in, so the OEM ECU will (presuming it has mappings that high, or at least sensible interpolation code) will still correct the fueling. If the MAF is post-turbo, when the pressure is above the natural value, the OEM ECU isn't going to compensate for the increased quantity and you're underfuel. To correct you'll need to create a map using RPM, load, MAF and MAP!
Further (conjecture) the high temperature of the air may also make the MAF under-read. Remember the MAF reads by the cooling effect of the airflow over a hot wire. Having unusually highly air temp may reduce the cooling effect.
Quote from: "mph"Moving post turbo means you'd really need a full ECU not a piggyback
Can't the e-Manage handle that? s:shock: :shock: s:shock:
QuoteTo correct you'll need to create a map using RPM, load, MAF and MAP!
The PFC needs only RPM and load, why would the e-Manage need more?
(I'm not saying you're wrong, just asking, cause I'm not familiar with the e-Manage, but many say it can do pretty much what the PFC can, except change rev limit s:lol: :lol: s:lol: )
Quote from: "Tem"The PFC needs only RPM and load, why would the e-Manage need more?
The PFC will need more than that - what it shows the programmer is something else.
Back to the plot in hand, you need to know how much air mass is in the cylinder to calculate your fuelling. A MAF pre-turbo can do this in isolation (though accuracy may not be great), whereas post turbo you'll need to combine the value with one from a MAP to get your value. If you can do this (and I'm not sure you can with a piggyback - though I'm happy for you to prove me wrong) then you'll end up with a more accurate picture.
you can do it with a piggyback because thast how mine and Seans run, we have the optional MAP sensor
strangely though, the new Hass kit has no MAP and the MAF post Turbo, it seems to run fine,.
Quote from: "mph"Quote from: "Tem"The PFC needs only RPM and load, why would the e-Manage need more?
The PFC will need more than that - what it shows the programmer is something else.
Back to the plot in hand, you need to know how much air mass is in the cylinder to calculate your fuelling. A MAF pre-turbo can do this in isolation (though accuracy may not be great), whereas post turbo you'll need to combine the value with one from a MAP to get your value. If you can do this (and I'm not sure you can with a piggyback - though I'm happy for you to prove me wrong) then you'll end up with a more accurate picture.
The PFC gets load from MAF and there's no MAP sensor, so it can't use that. That's why I assume e-Manage should run without MAP as well.
Sheez, s:roll: :roll: s:roll: it works fine pre AND post-turbo with MAF ,Emanage Blue and no MAP at all.
Moving the MAF post-turbo is preferable because it also houses the temperature sensor.
AFR is a relationship measured in weight. 12.5:1 is 12.5 lbs of air to 1 lb of fuel.
Its my understanding that moving the MAF (to anywhere) HAS NO EFFECT ON THE CALCULATION. In a hotwire MAF the amount of current needed to heat the wire is proportional to the mass of air moving into the engine.
The "mass" or weight is measured in molecules not 'flow' or 'speed' or 'density'.
It is by this very principle that a MAF based system automatically adjusts for altitude and barometic pressure. It compensates by design for changes in VE.
What does affect the calculation is the diameter of the tube in which the sample is taken.
However, a MAF based fueling strategy will always be limited by the maximun voltage required by the sensor. 5v in our case. Additionally, pressure (MAP) based fueling is superiour to MAF because ,under boost, fueling should be directly proportional to manifold psi and not TPS.
Uh oh! Obviously I'm wrong since you lot have working systems - sorry guys!
I'd still like to clear up my understanding though - having written the below it seems my understanding of basic physics is a bit lacking...
Quote from: "wts"The "mass" or weight is measured in molecules not 'flow' or 'speed' or 'density'.
I dissagree. The key thing I missed was that heat dissipation is also proporational to mass and therefore it'll work equally well pre or post turbo. However, flow (=velocity) is still important - if it weren't you wouldn't need to put fans on radiators or heat sinks for example. Therefore, it doesn't measure simply mass, but mass over time - the techies didn't call it "mass air flow" for no reason!
Back to basic physics: I still think my assertion regarding the potential to under-read is still possible: example, how much heat would the hot-wire (@ say 200C) dissipate (and therefore what the sensor reading would be) if air temperature was also 200C, as compared to if the air temperature was 0C?
Moving the temp sensor is definitely a good idea as it'll be reading the value it was intended for. However, has the OEM ECU been programmed to take account of the potential values it'll get? Can you use the value in mapping the eManage et al?
Lastly, I'm not sure if I've read you right: are you saying you can calculate fuel from MAP only? I wouldn't have thought that was possible, at least in a turbo car. Why? pressure means nothing without flow. Example: drive along and generate some boost then close the throttle body. MAP reads 'lots' of pressure, so therefore you should be adding fuel? No, as there's no air getting to the cylinder (as incidentally reported by a post turbo MAF - glad you moved it now!)
Quote from: "mph"Therefore, it doesn't measure simply mass, but mass over time - the techies didn't call it "mass air flow" for no reason!
Yeah, it measures mass/time.
Quotehow much heat would the hot-wire (@ say 200C) dissipate (and therefore what the sensor reading would be) if air temperature was also 200C, as compared to if the air temperature was 0C?
You can actually use a hotwire sensor to measure airflow which is hotter than the wire. It's the instrument (in our case the ECU) that limits whether it can handle the 200C and more or not.
Quoteyou can calculate fuel from MAP only? I wouldn't have thought that was possible, at least in a turbo car.
Yeah, you can, Toyota has stock factory cars that do that s;) ;) s;) The MAP sensor just needs to measure what's entering the engine and cannot be before the throttle plate.
Haha! I've still got a lot to learn about this stuff but I AM learning s:D :D s:D
Regarding MAF's: m http://www.kemparts.com/TechTalk/tt06.asp (http://www.kemparts.com/TechTalk/tt06.asp) m
QuoteAdjustments for air temperature and humidity are taken into consideration since they also affect the temperature of the heated wire or film.This sensor not only measures the volume of air but also compensates for its density as well.
Quote from: "mph"I dissagree. The key thing I missed was that heat dissipation is also proporational to mass and therefore it'll work equally well pre or post turbo.
Yes, temperature
does matter and is why the temp sensor is in the same housing as the hotwire.
QuoteHowever, flow (=velocity) is still important
Yes, velocity and pressure affect the mass of the incoming stream but they dont matter because, by design, a MAF detects the changes in mass. A VaneAirFlow sensor (VAF)would be a different matter tho and would be bolloxed if placed in a pressurized intake tube.
QuoteBack to basic physics: I still think my assertion regarding the potential to under-read is still possible
If your concerend about a calculation error due to the tempbulb being post I/C and the hot-wire being pre-turbo then read this. m http://www.spyderchat.com/phpBB/viewtopic.php?t=14864 (http://www.spyderchat.com/phpBB/viewtopic.php?t=14864) m
QuoteLastly, I'm not sure if I've read you right: are you saying you can calculate fuel from MAP only?
YES
QuoteExample: drive along and generate some boost then close the throttle body. MAP reads 'lots' of pressure
No, theres a vacuum in the manifold as soon as the throttle is closed, fuel is cut. LESS vacuum = more fuel. MAP sensors can also be used to measure barometric pressure so load calculations can factor in altitude changes.
Quote from: "Tem"Yeah, you can, Toyota has stock factory cars that do that s;) ;) s;) The MAP sensor just needs to measure what's entering the engine and cannot be before the throttle plate.
Rev3+ Mk2 Turbo, for one. Also a (relatively) popular mod on cars that use a hotwire MAF (like the 300ZX) - go to MAP and use a VPC to emulate the MAF reading for the stock ECU (assuming some piggyback device controlling fuelling).
Cheers guys for the informed replies. Looks like I've got some more bedtime reading to get through!