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Old 03-15-2010, 07:32 PM   #1 (permalink)
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To Blow Through the Mass Air Flow Sensors Or Not???

My plans are to place the MAF sensor in the pipe after the Blow Off Valve about 8" to 10" before the Throttle Body.

My reasons for wanting to try the Blow Through Set-Up.
- Accurate Metering
- Actual Air Temperature Going into the Engine
- Not having to Recirculate the Blow Off Valve


I Found this on Another Web Site

Blow Through Pros
- Fastest A/F Ratio Changes
- More Accurate
- Eliminates 99% of Idle Problems
- Meters Exactly how much Air is Going into the Motor, not how much is in the Intake.
- Easier to use Blow Off Valve
- Can use Atmospheric Blow Off Valve
- Totally Eliminates Recirculation Setups

Blow Through Cons.
- MAF more Prone to Heat Soak (can be minimized by using a good intercooler)
- If not Properly Placed on the Intake Side can cause Hesitation in Motor.
- Can be hard to hook up.
- Can get Oil in MAF from SuperCharger / Turbo Leakage.
- Can't use certain Methanol Injection Kits


Questions
- Who has Used this Set-Up???
- What's the Best Placement of the MAF before the Throttle Body???
- What's the Best Placement of the Blow Off Valve before the MAF???
- Any Likes or Dislikes???
- Any Tuning Issues???
- Any Idle Issues???


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Old 03-15-2010, 11:08 PM   #2 (permalink)
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I vote PULL THROUGH ..

MAF BEFORE turbo ... better all around Driveability, and no erroneous readings like on the blow through setups.

Pull through setup know exactly how much air the engine is consuming.
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Old 03-16-2010, 08:43 AM   #3 (permalink)
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Quote:
Pull through setup know exactly how much air the engine is consuming.

No it doesn't. The MAF uses the temp of the air (air is more dense at lower temps), and the air temp in front of the turbo will be very different from the air temp right before the throttle body.

Use blow through with the MAF, after the BOV, right before the throttle body.

Here you go: Maf Postion On A Turbo Set Up
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Old 03-16-2010, 10:29 AM   #4 (permalink)
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Quote:
Originally Posted by antISanISfreak View Post
I vote PULL THROUGH ..

MAF BEFORE turbo ... better all around Driveability, and no erroneous readings like on the blow through setups.

Pull through setup know exactly how much air the engine is consuming.
Do you actually run this setup on the IS300 and have it running well?

I don't know about this guy, but EVERY single successful kit or setup with the IS300 ECU has had the MAF in a blow through config!
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Old 03-16-2010, 10:35 AM   #5 (permalink)
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Blow Through Cons Disputed.
- MAF more Prone to Heat Soak (can be minimized by using a good intercooler)

Absolutely not for the IS300 MAF. It is a simple hot wire in a small plastic guide that has almost no mass and will not heat soak.

- If not Properly Placed on the Intake Side can cause Hesitation in Motor.

Your car is almost gauranteed to hesitate if you place the MAF in a pull through configuration.

- Can be hard to hook up.

O really? Uh...not for the IS300. Unless you change to a front facing supra style intake manifold?

- Can get Oil in MAF from SuperCharger / Turbo Leakage.

Oil is a non-issue for this MAF. I've run mine in blow through for over 30k miles. Never cleaned the MAF once. And there is definitely a very fine layer of oil mist all though the intake tract.

- Can't use certain Methanol Injection Kits

You can inject meth after the MAF. Again...non-issue.
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Old 03-16-2010, 10:41 AM   #6 (permalink)
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This is good information. ^
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Old 03-16-2010, 11:18 AM   #7 (permalink)
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Taken from the linked thread, pay special attention to this fact-
Quote:
BOV goes at least 6" in front of MAF
If not this distance, just the orifice of the BOV flange/pipe t'eed into your charge pipe will cause a turbulence. In my case there are not issues at any load above idle, but it causes lower MAF readings at idle causing fuel trimming and possibly a rougher idle.

x 3 on the placement of the MAF.
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Old 03-17-2010, 01:27 AM   #8 (permalink)
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YES, I DO run a PULL through MAF

NO the MAF does NOT figure out how much air is coming through by the Air's TEMP. It calculates by how much COOLING is being done to the hot-wire inside by the air passing over it, and how much AMPERAGE it takes to keep said wire at that a specific temperature!

-- Just like how a WIDEBAND A/F meter uses AMPERAGE to pump O2 in or out of the nerst cell to figure out what actual A/F is --

Seriously, I'm not a newb at this, and please don't try to talk to me as such. If you want to have a conversation, lets ... and i can back all my findings with everything with firsthand experience, not regurgitated info.

-- If you would please, Get an OBD2 Scan tool and use it in live data to tell me what your MAF's lb/min reading is at WOT in full boost. Mine is reading around 36-38 Lb/min.

Furthermore -- OE manufacturers place MAF pull through for the simple fact that it operates on air movement across the wire, not pressurized air being placed around it -- for an example, please refer to stock GTE MAF placement. ~ I don't know about you, but sitting in a hot room with stagnant air on a hot day makes me feel hot. Even if that room was pressurized, i'd still feel hot, maybe hotter ... when i turn a fan on i feel cooler as air moves across my skin and picks-up/removes heat from my body. Boosted air is stagnant ~ yes there is FLOW, but not enough that the wire can see and effectively be cooled, to give an accurate reading.

Also about hesitation --- on pre-turbo setups, its cause when the air passes back over the wire (in reverse) when the Throttle plate closes/bov closes, and the turbo is in Decel. Stock GTE MAF's have a hooded hotwire to prevent the re-pass over of AIR across the wire in these instances. Also, hesitation and Stall on pre-turbo MAF's is due to improper tuning and a poorly setup MAF clamp. When the BOV opens, the MAF sees a RUSH of what it believes to be "engine consumed" air and tries to compensate by dumping in more fuel to prevent a lean condition ~ thus a stall due to an overly rich condition because the engine did NOT infact consume the air, and actually need litte/no fuel because is in Decel, or maybe already at idle ... again a properly setup MAF clamp cures this.

pull through by-far yields best drive abilty and tune ability in and out of boost with the right know how and tuning.

blow through is simple, and requires little in the form of tuning out stalls and other slight hiccups because it doesn't ever get the chance to see whats happening before it -- blow through is EASY but shouldnt be recommended. - I actually feel that "kits" are sold with Blow-Through setups for EASE of sending a pre-configured ECU out with the setup. Every care is going to require a custom MAF Clamp that cannot be summed up in a general tune. therefore, set everyone up with a tune/kit that doesnt require such customization/headache.

Blow Through Pros DISPUTED
- Fastest A/F Ratio Changes
The MAF will interpret the pressure change/lack of are movement/velocity as a DECREASE of AIR consumption by the engine, and REMOVE fuel.
- More Accurate
WRONG .. the MAF becomes LESS accurate as velocity across the hot wire is reduced. Again, velocity across the wire yields MORE cooling thus MORE air volume. pressurizing the air around the wire does NOT constitute more wire cooling, it in fact does the opposite.
- Eliminates 99% of Idle Problems
Yes, because the MAF doesn't know the difference between stock and the turbo being added
- Meters Exactly how much Air is Going into the Motor, not how much is in the Intake.
WRONG ... read the above.
- Easier to use Blow Off Valve
I think you get the idea of why. MAF doesnt have a chance to read the air that escapes the BOV - and thus does NOT for the ECU to dump fuel.
- Can use Atmospheric Blow Off Valve
Ditto the above
- Totally Eliminates Recirculation Setups
Blah blah blah .. same "pro" recited 4 different ways


Quote:
Originally Posted by TeCKis300 View Post

Blow Through Cons Disputed.


- If not Properly Placed on the Intake Side can cause Hesitation in Motor.

Your car is almost gauranteed to hesitate if you place the MAF in a pull through configuration.
My turn to ask YOU now. Have you ever ran a Pull through setup and experienced this phenomenon for yourself? I have actually NEVER.

Quote:
Originally Posted by TeckniX View Post
Doing it as show in the picture (before the turbo) isn't all bad, but really it's done (putting the MAF after the turbo) as ease of use.
Once a person shifts and the bov opens up, a rich condition will be seen.

Most setup as picture above, should be setup as a recirculated setup, since the maf has already accounted for the air. If it gets vented to Atmosphere, then you're simply telling the ecu I calculated x amount of air coming in per the MAF, so the ecu allows for the appropriate fuel to go in for that x amount of air, yet, you're letting some of it out, resulting in a rich condition.
ALL as i mentioned earlier -- and this quote was taken from your poor selection of threads to link. I actually read that thread AFTER writing this whole post.

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Old 03-17-2010, 07:44 AM   #9 (permalink)
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Quote:
NO the MAF does NOT figure out how much air is coming through by the Air's TEMP. It calculates by how much COOLING is being done to the hot-wire inside by the air passing over it, and how much AMPERAGE it takes to keep said wire at that a specific temperature!
You need to do a little more wire checking before you talk. Where's our IAT sensor at? Oh shit could that be it, right there built into the MAF!

Quote:
OE manufacturers place MAF pull through for the simple fact that it operates on air movement across the wire, not pressurized air being placed around it
OE manufacturers use pressure sensors to meter pressurized air, they place the MAF pre-turbo for convenience, just look at the Supra.
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Old 03-17-2010, 09:25 AM   #10 (permalink)
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Either way a proper tune and decent EMS will get both ways to run the same.

Blow-through IMO since it measures what's being consumed by the engine, not what's being consumed by the turbo (including waste/excess).

Since hot wire MAFs are heated up anyways, they're not going to heat sink. If you understood how one worked you'd get this. It will, however, throw a slightly inaccurate reading if heated by an outside source, like turbo heat. Hot air from hot intake makes no difference, since the sensor's job is to read it for what it is anyways. The only innacuracy you'd get would be from the actual hot wire being heated by the turbo, which just won't happen. The hot wire also tends to burn off junk that sticks to it, leaving a fine residue that will typically get blown off later. They keep themselves clean like an oven has a "clean" setting.

Remember, it measures mass, not volume. Density can be increased with pressure or lower temperature. High pressure at high temperature and low pressure at low temperature make the same mass (for this example) and will require the same fuel. But the fact remains that one is boosted hot air, and one is naturally aspirated cold air. Placing the sensor before the turbo means you're measuring the low pressure cold air (including what's wasted), and placing it after means you're measuring the high pressure hot air. Since the sensor works perfectly in either scenario, it only makes sense to mount it where you'll get a more accurate reading. Pull through seems to me to make more sense for OEM applications, but blow through makes more sense if you're adding a turbo to an otherwise non-turbo engine (and computer). If the computer starts adding extra fuel because it thinks it's breathing the air that's actually getting dumped, it'll spike richer when you let off the throttle, resulting in backfiring and wasted fuel...

It's the same with supercharged carbureted motors... 6 of one half dozen of the other whether to run a blower and then a carb, or a carb then a blower. Carb first you're boosting fuel and air (harder, less efficient), blower first you have to get a different carb or swap floats to handle the pressure... etc etc. (not expecting some of the import guys here to understand carburetors though - that's another lesson lol)
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Old 03-17-2010, 09:42 AM   #11 (permalink)
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Blow through.

This way you get accurate ait temp information. Ideally the IAT sensor would be in a runner on the manifold but that is not the case here so at least you can get the most accurate incoming air temps this way. As stated make sure there is sufficient distance between the BOV and MAF. I would recirculate it if you could and save the energy. This also helps prevent surge when you have too large of a compressor for the application.
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Old 03-17-2010, 10:04 AM   #12 (permalink)
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I'm glad you came back and actually tried to support your position. I agree with you that too many newbs simply regurgitate a position + FTW, rather then first hand information.

Glad you got the pull through style to work, but you almost supported the blow through as much if not more than the pull through style - stating it's 'easy'.

I won't get too far into your explaination of MAFs, other than to say, yes, technically it's more accurate not to read boost, but you're understanding is not completely correct as it reads MASS. And there is the small issue of IAT as stjarvis points out.

And MAF clamps... They're for the purpose of hiding what is considered out of range readings to the stock ECU at speed. First time I've heard of using them to cover tuning for blow-offs?

Irrelevant of all these arguements about the proper usage of MAFs... and whether the supra uses a pull through (because the supra ECU is tuned for that + uses a MAP). The real reason is simply because the IS300 ECU is expecting MAF (and IAT) to be placed a certain distance from the cylinder. When you place it 4X as far down the plumbing... there will be hiccups as the stock ECU is expecting cylinder conditions to occur a certain fixed time differential after it's read. And when you begin messing with the flow (blow-offs) and temps (turbo adding heat / intercooler) from what is read after the MAF....






Quote:
Originally Posted by antISanISfreak View Post
YES, I DO run a PULL through MAF

NO the MAF does NOT figure out how much air is coming through by the Air's TEMP. It calculates by how much COOLING is being done to the hot-wire inside by the air passing over it, and how much AMPERAGE it takes to keep said wire at that a specific temperature!

-- Just like how a WIDEBAND A/F meter uses AMPERAGE to pump O2 in or out of the nerst cell to figure out what actual A/F is --

Seriously, I'm not a newb at this, and please don't try to talk to me as such. If you want to have a conversation, lets ... and i can back all my findings with everything with firsthand experience, not regurgitated info.

-- If you would please, Get an OBD2 Scan tool and use it in live data to tell me what your MAF's lb/min reading is at WOT in full boost. Mine is reading around 36-38 Lb/min.

Furthermore -- OE manufacturers place MAF pull through for the simple fact that it operates on air movement across the wire, not pressurized air being placed around it -- for an example, please refer to stock GTE MAF placement. ~ I don't know about you, but sitting in a hot room with stagnant air on a hot day makes me feel hot. Even if that room was pressurized, i'd still feel hot, maybe hotter ... when i turn a fan on i feel cooler as air moves across my skin and picks-up/removes heat from my body. Boosted air is stagnant ~ yes there is FLOW, but not enough that the wire can see and effectively be cooled, to give an accurate reading.

Also about hesitation --- on pre-turbo setups, its cause when the air passes back over the wire (in reverse) when the Throttle plate closes/bov closes, and the turbo is in Decel. Stock GTE MAF's have a hooded hotwire to prevent the re-pass over of AIR across the wire in these instances. Also, hesitation and Stall on pre-turbo MAF's is due to improper tuning and a poorly setup MAF clamp. When the BOV opens, the MAF sees a RUSH of what it believes to be "engine consumed" air and tries to compensate by dumping in more fuel to prevent a lean condition ~ thus a stall due to an overly rich condition because the engine did NOT infact consume the air, and actually need litte/no fuel because is in Decel, or maybe already at idle ... again a properly setup MAF clamp cures this.

pull through by-far yields best drive abilty and tune ability in and out of boost with the right know how and tuning.

blow through is simple, and requires little in the form of tuning out stalls and other slight hiccups because it doesn't ever get the chance to see whats happening before it -- blow through is EASY but shouldnt be recommended. - I actually feel that "kits" are sold with Blow-Through setups for EASE of sending a pre-configured ECU out with the setup. Every care is going to require a custom MAF Clamp that cannot be summed up in a general tune. therefore, set everyone up with a tune/kit that doesnt require such customization/headache.

Blow Through Pros DISPUTED
- Fastest A/F Ratio Changes
The MAF will interpret the pressure change/lack of are movement/velocity as a DECREASE of AIR consumption by the engine, and REMOVE fuel.
- More Accurate
WRONG .. the MAF becomes LESS accurate as velocity across the hot wire is reduced. Again, velocity across the wire yields MORE cooling thus MORE air volume. pressurizing the air around the wire does NOT constitute more wire cooling, it in fact does the opposite.
- Eliminates 99% of Idle Problems
Yes, because the MAF doesn't know the difference between stock and the turbo being added
- Meters Exactly how much Air is Going into the Motor, not how much is in the Intake.
WRONG ... read the above.
- Easier to use Blow Off Valve
I think you get the idea of why. MAF doesnt have a chance to read the air that escapes the BOV - and thus does NOT for the ECU to dump fuel.
- Can use Atmospheric Blow Off Valve
Ditto the above
- Totally Eliminates Recirculation Setups
Blah blah blah .. same "pro" recited 4 different ways




My turn to ask YOU now. Have you ever ran a Pull through setup and experienced this phenomenon for yourself? I have actually NEVER.



ALL as i mentioned earlier -- and this quote was taken from your poor selection of threads to link. I actually read that thread AFTER writing this whole post.
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Old 03-17-2010, 10:53 AM   #13 (permalink)
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Should have seen this earlier.

Sorry, but reason not to go pull-through:
Switched over to a TT MAF.

Quote:
Originally Posted by antISanISfreak View Post
I vote PULL THROUGH ..

MAF BEFORE turbo ... better all around Driveability, and no erroneous readings like on the blow through setups.

Pull through setup know exactly how much air the engine is consuming.
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Old 03-17-2010, 11:37 AM   #14 (permalink)
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good discussion.. but a lot of word vomit.

the MAF has an IAT to compare incoming air temp against the hot wire. it then adjusts the hot wire temp accordingly. it doesn't actually use it for any trimming adjustments more than a gauge as too weather the wire is actually being cooled relative to IAT. the wire in the hot-wire is kept at X temp above ambient air temp. they have a relationship.

i understand exactly how a MAF works & how it doesn't.

MAP sensors measure density - not volume. they use Speed Density method.

MAF measures volume in lb/min.

i do say Pull through MAF, and furthermore you DO still need a MAP for tuning. Running a Blowthrough is the completely wrong way to utilize the capabilities of the sensor, and will ultimately result in bad drive ability.

ALSO - this in this discussion, everyone SHOULD keep in mind that the MAF is only being used out of Boost, and that its not the sensor/tool used for tuning. MAP sensor FTMFW.

Last edited by antISanISfreak; 03-17-2010 at 11:42 AM.
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Old 03-17-2010, 11:53 AM   #15 (permalink)
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iTrader: (23)
So is it established that a hooded Supra MAF is needed regardless of BOV recirc or atmospheric? What piggyback systems have features to clamp the MAF in off-throttle situations, and how programmable/versatile is it?

I went the 'typical' route, in the charge pipe about 12-13 from the TB, I didn't give the original location on the Tnetics kit a try. Unichip is hush hush on all of the features and ownership of the tuning software, so I do not know how they addressed possible issues of their placement, nor did I see the possible issues as I did not run the setup.

As for drivability, it is great except for my BOV turbulence at idle that will be fixed when my lazy ass moves the BOV (not a problem when using a standalone of course, 100% of the time being speed density).

Tuning wise with the MAF needing to be clamped in most boost regions, the tuning method essentially converts from a mass air flow to speed density via my EMU's MAP sensor.

Seems to be plenty of success with the charge pipe MAF placement/blow through, not so much with pull through.

This is a great thread, lots of great information for peeps new to these concepts.
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