MAF Placement?

[WizardBlack]

IMHO, if you have the money for an RB you aught to be using a standalone. Blowthrough works but only if you have enough control of the ECU. A factory car likely has an airtemp sensor in the manifold or it has a carefully calibrated adjustment for hotter air temps based on boost pressure, etc. This is all highly dependent on the factory intercooler, turbo, etc.

 

MAF-wise, I will explain a bit of the MAF dynamics so ppl can understand how to place the MAF. When fluid (liquid or gas) flows through a pipe, it starts out very disorganized. As it continues to flow through the same pipe, it starts to take on a velocity profile with respect to distance from the wall of the piping. In other words, the air flowing through the very center of the pipe flows a lot faster than the air flowing along the wall of the pipe. This is the velocity profile. When you have a factory setup, the MAF and ECU are carefully calibrated for the velocity profile that the intake system experiences. It is all made to stay consistent and predictable. The piping BEFORE the MAF is crucial. Especially the airbox design, how many bends there are, etc. Bends will cause the air to crash to the outside edge of the bend after the bend and it will take a while to reestablish the same profile, so having a MAF after a bend is bad. Right before the bend will also do it a bit. Having a MAF not at the center of the piping is bad. Having the MAF somewhere that the center of the pipe reads hardly anything is bad (such as RIGHT after the start of the pipe; the air will flow into the pipe like a toilet flushing and won't read much at the center or it will be chaotic).

 

For idle, you should have pretty solid control of your idle solenoid, stepper, whatever it is. In addition to that, you can use an authorized range of about 10 degree timing plus or minus to also step in after the idle circuit is adjusted to about half of it's authority. If you want it to idle smooth, run it just a tad rich. If you want it to idle efficient, you will need more IAC to do it and authorize and bit larger rpm range to wander around in. If you want it to sound cool and lopey, narrow the rpm range, use timing and leave it leaner so you also don't foul the plugs. Colder plugs and bigger injectors will require the timing unless you want to raise idle rpm (which i would not do too much). If it retards too much while idling, you will cook your engine bay.

Edited December 29, 2013 by WizardBlack

[mtnickel]

I've read theses air straighteners can really clean up the maf signal....

 

http://www.ebay.com/itm/3-5-88-9mm-OD-x-5-Air-Straightener-Screen-25-6-35mm-open-cell-/251337605931?pt=Motors_Car_Truck_Parts_Accessories&hash=item3a84e3832b&vxp=mtr

 

I don't know that this is the exact one to get, but if you read up a bit, it organizes the air and stabalizes the maf signal.

 

As an alternative to a standalone, if you are ok at soldering Nistune is a pretty good option. The RB25 Ecu isn't readily compatible, but there is a writeup on converting a Z32 ECU to work (cutting a few board traces, soldering a few resistors, etc). After that you have the option of buying the full nistune board, burning chips a few times to get a decent tune started, or like I am doing is to get an ostrich eprom emulator. Picked up the emulator for about $150, Z32 ecu for $40 (you can find them cheap if you look hard enough), $200 for the nistune software, and $40 for a consult cable adapter to USB. About $400 and a little work, but certainly cheaper than a $1000+ standalone.

[ihiryu]

Wizard,

 

I'm a little confused.  On my setup I have the MAF in the grille, So it goes; Cone filter, MAF, coupler, 90 degree aluminum pipe, straight pipe, turbo.

 

On the past few nissan engines I used, I've put the filter directly on the MAF with no problems.

[zster]

Good post wizard, mtnickel. I am ready to use standalone if stock system cannot work. One question? Do the honeycomb air straighteners that mtnickel suggests work? My system has long runs of piping from front of intercooler to MAFs. The MAFs are 18 and 12 inches from turbos with a bend or two. Seems to work okay, but I want better. Have a good radiator and fan system, everything runs cool.

The problem my build has is inconsistency, Idles great, runs great. Next time high idle, miss at high rpm. Haven't found anything loose yet or air leaks. Perhaps air temperature differences as my intake slightly blocks my FMIC. The air entering MAFs should be cool. When car is behaving badly it seems to be a lean condition though not positive. Anyone else having these issues?

[WizardBlack]

Wizard,

 

I'm a little confused.  On my setup I have the MAF in the grille, So it goes; Cone filter, MAF, coupler, 90 degree aluminum pipe, straight pipe, turbo.

 

On the past few nissan engines I used, I've put the filter directly on the MAF with no problems.

Not ideal, but I guess it depends. Some cars have different factory setups and therefore the stock ecu is built differently. The best thing you can do is replicate the length, bends and placement of the stock setup.

[WizardBlack]

Good post wizard, mtnickel. I am ready to use standalone if stock system cannot work. One question? Do the honeycomb air straighteners that mtnickel suggests work? My system has long runs of piping from front of intercooler to MAFs. The MAFs are 18 and 12 inches from turbos with a bend or two. Seems to work okay, but I want better. Have a good radiator and fan system, everything runs cool.The problem my build has is inconsistency, Idles great, runs great. Next time high idle, miss at high rpm. Haven't found anything loose yet or air leaks. Perhaps air temperature differences as my intake slightly blocks my FMIC. The air entering MAFs should be cool. When car is behaving badly it seems to be a lean condition though not positive. Anyone else having these issues?

You have bends right before the MAFs; particularly that one. It will not read as much air as it should and therefore run lean in that condition. Be advised that the higher the air velocity the more the air profile will be wrong for the MAF because the air can't 'make the turn' and restabilize as fast as slow, lazy air. In other words, you will see a very bad bend cause issues at most operating conditions, but a bend that is 'almost Ok' will only show up at high load (like you are seeing).

Honeycomb straighteners can help but won't solve every issue. Lots of factory cars use them or even have them built into the MAF.

Your upper MAF has a 'bend' right AT the MAF from poor amount of space to fit it in. Not good. The lower one has a bend a bit upstream that may be a problem. One big issue is they don't match. IMHO the best solution is to ditch all the MAF stuff and run speed density to resolve the issues. A MAP based system is better for a heavily modded car and particularly one that changes with tweaks all the time. On a turbo car, your timing is related to engine speed and air density. Your air:fuel target is also variable based on engine speed and air density. Therefore a speed density setup is a more direct solution. As long as you don't buy a super simple ECU you will have plenty of closed loop control to make it run clean.

Edited January 2, 2014 by WizardBlack

[WizardBlack]

I've read theses air straighteners can really clean up the maf signal....

 

http://www.ebay.com/itm/3-5-88-9mm-OD-x-5-Air-Straightener-Screen-25-6-35mm-open-cell-/251337605931?pt=Motors_Car_Truck_Parts_Accessories&hash=item3a84e3832b&vxp=mtr

 

I don't know that this is the exact one to get, but if you read up a bit, it organizes the air and stabalizes the maf signal.

 

As an alternative to a standalone, if you are ok at soldering Nistune is a pretty good option. The RB25 Ecu isn't readily compatible, but there is a writeup on converting a Z32 ECU to work (cutting a few board traces, soldering a few resistors, etc). After that you have the option of buying the full nistune board, burning chips a few times to get a decent tune started, or like I am doing is to get an ostrich eprom emulator. Picked up the emulator for about $150, Z32 ecu for $40 (you can find them cheap if you look hard enough), $200 for the nistune software, and $40 for a consult cable adapter to USB. About $400 and a little work, but certainly cheaper than a $1000+ standalone.

That honeycomb is too coarse to really do it. And not long enough. IIRC even my RB25 MAF has a honeycomb in it. I could be wrong. I have seen a lot of Subaru and MItsu MAFs over the years too. Each cell on a stock honeycomb is usually about 1/4" to 1/8" cells IIRC and more like 1.5"+ in depth..

 

IMHO is you have soldering capability you'd be better off building a Meagsquirt. It is not the best in tuning control but it has enough to get the job done. Better than an aging ECU that could lose a capacitor or end up dying from the mods and flashes only to end up with a heavily changed stock ECU.

Edited January 2, 2014 by WizardBlack

[zster]

  Thanks, maybe I'll go with AEM it will work with my AEM  boost control. Should be simple though not as cheap as I would like. Anyone using AEM management?

[ihiryu]

I really love AEM, I just don't have AEM money at the moment.  

[WizardBlack]

I was AEM certified years ago. AEM works very well. All it is inside the box (at least series 1) is a universal standalone (built with the help of Link IIRC) with edge pins to connect to an adapter board for the specific car. I especially liked the ability to control boost target with the throttle. I built a few road race type cars with that in mind to try to linearize a "slightly bigger than stock" turbo for mid corner control. They also have very good idle control and closed loop fuel, boost, etc control. Even though AEM guys are in Kalifornia and can't make a base map with cold weather capability for crap, the boxes have plenty of features to get it sorted. It makes me chuckle; I was once on a trip to Cali for a customer who was racing in a minor event on Streets of Willow. Magazines would be there and everyone from the Cali shops (which is all who ever come to those events covered by the Cali based magazines) came early to put all their shop stickers on the cars before going out. A Sparco Evo was trailered there covered in "S" vinyl and fiberglass, etc. It was ~40's *F and they could NOT get it to start. When they finally did I thought it was going to bang the rev limiter.

I have tuned EVO's, WRX's, STI's, etc. on an AEM box lots of time. I can't complain about them whatsoever. I don't care for their service somewhat, but the box does what it's supposed to. Innovate is very good for widebands as well.

I have not messed with AEM since when Series II (IIRC) had been out for just a little while. They are a solid setup and will easily handle boost control duties with just a cheapy solenoid. You can sell whatever else you have for boost control; the box will handle it directly and it is recommended to do it that way. MOTEC is better IMHO, but it's close and depends on the application. I have built MS2 boxes and it will work just fine. If you are newer to the game, I'd go for a prebuilt MS2 setup if they have the RB sensors worked out.

Edited January 3, 2014 by WizardBlack

[WizardBlack]

Can some one explain what the turbulence from the turbo do to the maf signal in detail? I currently have mine about 7-8" from the turbo but mine idles fine. My problem is that the ECU starts to freak out as the car warms up and retards the timing as if it is getting a lot more air than it is really getting. When I first start the motor from cold state everything looks normal. The timing is at 15 degrees like it should be but as the motor warms up the timing starts to pull back until it is below zero. There is a Red/Green indicator at the bottom of my consult that tells you if it is running lean or rich and once the motor has warmed up it stays Red/Lean and the motor wont make any power unless the CAS is fully advanced. I have been frustrating my self with this problem for about a year so if anyone has some insight please let me know.

Sorry I missed this one. I know it's a bit old but it would help either you or someone else. The turbo should not affect it much at all. The turbo will always be pulling air unless you have no BPV (which is a problem in itself) or you are using a blowoff valve (also a problem). Pullthrough MAF and BOV doesn't mix. If MAF is  6~8 inches from a turbo inlet it should be fine. For idle, you should have more air and timing to warm up (and shoot for slowly sliding from 11.5:1 to 13.5:1 while the O2 sensor is warming up and you are open loop or it's closed loop but not close enough to warm coolant temp yet). Once warm, timing should back down to circa 10~15 degrees depending on the bore diameter of the engine (more bore, more timing). If timing falls below that consistently, back off your air (idle circuit, IAC, stepper motor, whatever). Air fuel ratio should be the left alone to hit the A/F target. In other words, you get rough idle rpm target with the air control (standalones should have closed loop idle timing control OFF to get it tuned). Next you use timing for fine idle control (~10 degrees authority progressively fed in until it's ~500 rpm off target with 100~200 rpm deadband at target should get you close). Lastly you let the A/F target simply shoot for a fixed ratio (14.7:1 most of the time). You don't use fuel to control idle. You use air (coarse adjustment) so that the timing (fine adjustment) averages out to where it should be.

A stock ECU (flashed or modded or whatever) will have both air and timing adjustment. By this I mean "Idle RPM Error rpm vs. Idle Air Position Correction %" and "Idle RPM Error rpm vs. Timing degrees" or something of that nature. Many standalones either don't have timing adjustment or it isn't implemented by the tuner, but a stock ECU is doing both most of the time.

 

In your case, it sounds like the target RPM is lower than you think or the Idle Air Circuit (of whatever type) is not tuned right or working right. It sounds to me like it won't pull air closed enough (ie., remove air) since the ECU is pulling timing to get RPM's down and it's lean because the IAC is stuck open too far (past the authority of the closed loop fuel control). All in all, take your IAC apart and see if it's clogged with soot and clean it. Otherwise, if it's an RB I think you have some rubber hoses going to/from it that you can pinch down a bit with vise grips to slowly see if it helps it stabilize. IIRC the RB also has a pop open additional air circuit for cold start that could be non-working or stuck open. Or you have a manifold leak.

Edited January 3, 2014 by WizardBlack

[aongch]

I'm setting up for ECU upgrade soon. Question for Wizard, since you're very familiar with AEM, do you recommend this, or any other reliable options for tracking with some sustained high rpm on local circuits? Haltech, Nistune?  Below is my set up and MAF locations and ECU. Also my dyno results on AFR, consistent with no major peaks and valleys. Idles a little high at 1,200 but steady. Goal is 350whp. Can I ditch the MAFs since tight fit as is?

 

My 'fun' track project is also in this RB forum, for more info.

 

 

 

Edited December 9, 2014 by aongch

[ihiryu]

Ditch the MAF.

 

A lot of people are using ECU Masters Piggy back to get rid of it.  A lot of drift guys around here have used it with great success.

 

http://ecumasterusa.com/

 

I'm not a dealer for them yet, but have been eyeing the hell out of them.  THeir standalone kit is 1200 bucks.