Blow Through MAFS?

Post by **Cyt0teC** » Fri Dec 06, 2002 6:45 am

Anyone see anything wrong in placing the MAFS close to the TB, and putting the BOV about 6" coming off the IC? (turbo ka application)

I could run atmospheric BOV and not have to worry about piping from the BOV. Also, I would think having the MAFS meter the mass of air directly before the TB would be more accurate then before the turbo.

I know there are proponents for both, but is one technically more sound than the other? (blow through vs draw through)

What i've read, is there may be issues with the MAFS metering air as it flows backwards towards the BOV when it vents. Wouldn't having the MAFS directly before the TB solve that. I suppose I'd run into the issue of the MAFS disrupting the air into the TB.

BTW - using a z32 MAFS and 1st gen dsm BOV <--- yes I'm aware of the leak at idle.

Any comments or suggestions? tks

Post by **WDRacing** » Fri Dec 06, 2002 6:45 am

I tried this on my Skyline, The car idles like crap. But I'm sure there are better MAFs and better ECU's to read them. As far as open atmosphere BOV's causing idle and stall problems. It comes from the over rich condtion created when the air is released after the MAF has told the ECU that its coming. Putting the MAFS behind the BOV in theory would fix this. But Most ECU's compensate for this nowadays anyway.

WD

Post by **themadscientist** » Fri Dec 06, 2002 6:45 am

Here is the problem I forsee. Not to insult you but to illustrate the reson behind my opinion a quick explanation of how the MAF works. It heats a wire suspended in the incoming airstream to a specific temperature. The air coming in cools the wire and it takes additional voltage to maintain the wire at the set temp. This gives the computer the info it needs to consult tables and pick settings for fuel injection to go with that air. Now you just plugged it into a hot, high pressure environment which is hostile, transient and often filled with contaminant like oil from worn turbo seals or PCV hoses which by itself is not a dealbreaker but which is sure to cause the sensor to eventually fail. Also the tables in the computer were not set with this situation in mind and even if you got the air back down to ambient by the time it hit the sensor and the pipetract was surgically clean the ECU would still have to be reprogammed. Impossible? of course not but it sounds like a lot of additional BS for little if no gain.

Post by **CurlyStooge** » Fri Dec 06, 2002 6:45 am

wont work. The MAF needs to be placed atleast 6" (maybe 12, cant remember, lol) from the throttle body to work properly. The constant adjusting of the TB will cause pulsing and throw off the reading the MAF makes. This will usually cause the engine to die unexpectantly. The MAF also cant be placed after the turbo for any reason or anywhere near the BOV. All equal reasons to being placed near the TB. The only full proof way to clear up this problem is to lead back the air that the BOV releases, or get a stand-alone system (maybe wait til AEM releases an EMS for nissans) that switches the engines management to Speed/Density.

Post by **Movingviolation240** » Fri Dec 06, 2002 6:45 am

my MAF was about 5in from my TB and the BOV was on the other side of the intercooler. The car ran fine and never stalled when the BOV opened (unlike before when it was drawthrough). The only problem I had was when running over 15psi, then it would run a bit rich.

So depending on how much boost you run you'll be fine

PaulOrlando, FL

Post by **CurlyStooge** » Fri Dec 06, 2002 6:45 am

Movingviolation240 wrote:my MAF was about 5in from my TB and the BOV was on the other side of the intercooler. The car ran fine and never stalled when the BOV opened (unlike before when it was drawthrough). The only problem I had was when running over 15psi, then it would run a bit rich.

So depending on how much boost you run you'll be fine

PaulOrlando, FL

Is that your RB25 swap?

Post by **gyfer** » Fri Dec 06, 2002 6:45 am

Originally posted by themadscientist "].....The air coming in cools the wire and it takes additional voltage to maintain the wire at the set temp. ...

errr... correction. When more air pass through the wire, the cooler it is. It is less resistance when metal is cool, and this allow more voltage to pass thru wire, and sent to ECU. ECU sees voltage increase ( more air coming it... because cooler ) , increase fuel.

It don't take any voltage to maintain wire at set temp.

You need "smooth" air for MAF to calculate air correctly. MAF building too close to Throttle Body will cause turbulance and disturb MAF.

The real problems is our MAF don't see boost.

and even if you got the air back down to ambient by the time it hit the sensor and the pipetract was surgically clean the ECU would still have to be reprogammed..."

there is no 'by the time'When you are boosting and high revving, the air is flowing so fast that you get back what you pass back right away. At 420cfm ( a normal size turbo flow rate), you are pushing near 7 cubic foot per second.... that's about a can of beer per second !

Post by **themadscientist** » Fri Dec 06, 2002 6:45 am

exactly my point, you have no chance of making it read right without tuning the coputer for the new environment it is measuring in. At any rate just get a engine management system or VPC, it isn't worth the trouble moving that pathetic little sensor around and dealing with th problems that creates. I did it on my old Skyline but that had a shutter-door style flowmeter not a hotwire and I was constantly fiddling with the settings.

Post by **Tony Starks** » Fri Dec 06, 2002 6:45 am

Is it true that you can upgrade to a Cobra MAFS,Q45 MAFS,or Z32 300ZX MAFS?How would you go about doing that?Does everything plug up?Do you need custom connectors?Is there anything that needs to be done to the ECU?Thanx

Post by **SSDwellah** » Fri Dec 06, 2002 6:45 am

Well I'm sure the Mustang Cobra MAFS doesn't just plug up (splicing required) but I'm not sure about the other Nissan MAF sensors. I am fairly sure that you will need an OEM ECU reprogram (or at least adjustment of your aftermarket A/F controller if you have one) with any of them and definitely with the Cobra sensor.

Post by **themadscientist** » Fri Dec 06, 2002 6:45 am

yes you have to juggle wires and reprogram the puter to account for the new flow meter. You might be able to trim it with a S-AFC if you are good though. The E-manage and PowerFC have the ability to adjust for different flowmeters in a pulldown menu. Ask Moving violation, he has the E-manage and i beleive a 300zx AFM, he could help you with the wiring.

Post by **C-Kwik** » Fri Dec 06, 2002 6:45 am

There is no significant reason why a blow-through MAF would not work. A hot-wire MAF reads the volume of air passing through it sice the MAF is a known diameter and the amount of voltage needed to maintain the hot-wire temperature is directly related to the amount of air that passes through the MAF. And yes, it does take more voltage to maintain the temperature of the hotwire because it is at a much higher temperature than the air passing through it. Since the temperatures differ, heat will be transferred from the hotwire to the airstream, thus lowering the temperature of the hotwire. If the voltage is not increased, the hotwire will not maintain the same amount of heat.

Some care should be taken to prevent turbulent flow, and you may want to run a catch tank for the crankcase air, or even run it open and not route the crankcase air back into the airstream. Secondly, the MAF does have a built-in self-cleaning feature. The hotwire is heated up very hot right after shut down to burn off any contaminants so for light amounts of crankcase vapor, it should be negligible.

Post by **detforme** » Fri Dec 06, 2002 6:45 am

i juct got my car running with a blow through, and it runs great. just my 2 cents.

Blow Through MAFS?

Blow Through MAFS?

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