PDA

View Full Version : MAFS Blow Through



forcefedS13
03-14-2006, 08:15 AM
I have spent an hour searching for the answer, with no complete answer.

Im doing an upgrade and want to know the benefits of using the blow through MAFS setup.

What im looking for is to disconnect my recirculated BOV.

For relevence here is my setup:

GT2871R .64AR
Grex 1.2mm Head Gasket
Deatschwerks 740cc injectors
HKS Step1 Cams (264 10.5)
Peak Performance Bottom mount tubular Manifold
Z32 MAFS
Custom aluminum intake
Blitz LM FMIC
Greddy Hotpipe and BOV
MR 02 housing

What i want to do is see if i can have enthalpy tune the ecu so that i can run an open atmosphere BOV without running excessively rich.
Ive heard alot about the "blow through" design and want to see if this will help me or hurt me based on my setup. The car will be weekend driven for fun, seeing the track some.

I once ran the BOV unrecirculated, and it ran rich as hell. I could smell fuel 40 feet away from the car. And i kept throwing flames between shifts. With the new setup i was hoping to eliminate this issue and maybe simplify some things.

The only bad ting is that my Blitz FMIC piping is 3 inches in diameter and putting the MAFS on the pipe would cause a bottle neck before the throttle.

What do you guys think? Anyone have experienc3 with this setup? Thanks again in advance for all input.

S15xedS13
03-14-2006, 08:26 AM
You could always use a MAFS translator and use a GM 3bar MAP sensor instead...

forcefedS13
03-14-2006, 08:32 AM
I have no experience with that at all. I do know that it will force me to run engine management. I know somoeone that has it, and he was telling me how great it is, but its not for me.
Id rather stick with MAFS with this setup, but thanks for the input anyway.

sr20goofus
03-14-2006, 08:36 AM
You could always use a MAFS translator and use a GM 3bar MAP sensor instead...



i just did a search, i see there is a kit for the DSM's and such, has anyone used this unit on an SR before?

luka
03-14-2006, 08:55 AM
blow through => air pushes it's way through (ie between turbo / throttle boyd)

draw through => air is sucked through (between filter / turbo)

I've heard a lot of ray-tay-tay nah-nah-nah about this subject.

some say you can just relocate your MAF and change it from draw to blow... but I don't think it's that simple

I'm curious if anyone runs thier Z32 MAF blow-through and if it actually works? and if it was only a matter of relocation?

forcefedS13
03-14-2006, 09:04 AM
Thats exactly my question...what are the benefits of Blow Through?

And, is there any way to run atmospheric BOV without switching to MAP??

killjoy
03-14-2006, 09:22 AM
I for one would love to switch back to map and keep my rom tune, but I just don't think that will happen.

forcefedS13
03-14-2006, 09:40 AM
Why cant you keep the MAP setup?
And, what are you planning on running without it, blow through?

killjoy
03-14-2006, 10:05 AM
Nissans don't have a MAP from the factory, they have a MAFS.

forcefedS13
03-14-2006, 10:23 AM
I know that, it sounds like you were running MAP on the SR before, at least thats what i assumed by your post.

what im asking is, why cant you run the map on your SR now, and what are you going to run the blow through or draw thru?

killjoy
03-14-2006, 10:25 AM
I had a haltech before with a map setup, that I can't use anymore becuase that car got jacked.

I have ordered an enthalpy tune for the currect car and upgrades, and would love to be able to use a map setup, but the functionality isn't their unless i switch back toa full standalone or badbiki

forcefedS13
03-14-2006, 11:11 AM
So are you going to run the drawthru or blowthru MAFS setup?
Im just wondering because im thinking of doing it, although i think the MAFS may cause a bottle neck due to my 3inch piping.

240Shorty
03-14-2006, 11:25 AM
many ppl have done this in the past. i ran mine for 6 months and didnt re-tune for it. i had a pfc with a datalogit and my a/f didnt change at all. hybridynamics has done this also on their GT30R setup. i searched this subject forever ago and found info on it. you just need to look. Geoff at full-race has done it also. just look at his gallery pictures. you can see how he set his up. everyone made a big deal about how much straight piupe to have before and after and i had practically none. i dont think its as hard as everyone thinks. i didnt have issues and neither has anyone else that i have talked to that had it. you just need to make sure that the "box" part of the Z32 maf doesnt pop off if you are running excessive boost. just do it and see what happens. my guess is itll work. also dsm guys do this too. just make sure it is atleast 6 inches from the throttle body.and yes its helps with a open atmo bov as long is it is in the piping before the mafs. not between it and the throttle body.

Voltron
03-14-2006, 11:54 AM
I did a lot of searching on this subject as well before I went to blow through. Some people seem to think you need a re-tune, but most do not. Lots of people outline all sorts of rules about piping diameter and length of pipe before and after, and bends etc. I don't know about that, but here is what I have done:
http://i26.photobucket.com/albums/c121/GoonDriver/IMG_4359.jpg

In that photo, I have a N62 MAFS and the ECU tune is from Enthalpy. This is my current setup that I have not been able to drive because of other issues, so I can't say anything about how it runs. However, previously I had the stock KA MAFS in the exact same place and position with a JWT ECU tune and the car ran brilliantly.
Doing my own research on this subject, I came across a lot photos of different setups. There where quite a few variations with piping before and after, bends, and distance to throttle body. No one as far as I could tell reported any ill running changes after switching to blow through. I came to the conclusion that the MAFS placement is not as sensitive as people seem to think.

forcefedS13
03-14-2006, 11:59 AM
That was great information, you guys answered every question. My own theory makes sense now, the whole Mass Air after the BOV instead of before it idea.

Thanks again.

240Kompressor
03-14-2006, 01:29 PM
I am running blow through on the KA. No one mentioned the small benefits as far as I saw. If you develop a boost leak after the turbo, but before the MAFS, the car will still run as normal. If a pipe pops off, it will run normal, though slower. If it were draw through, any leaks after the Mafs will cause some decrease in runability and a pipe blow off will not run at all.

Of course, the better atmospheric BOV operation was discussed.

One negative is more possibility of contamination with oil if oil gets past your turbo. In which case it can be cleaned periodically. You may have to relocate the BOV depending where it is mounted if you are already draw thru.

forcefedS13
03-14-2006, 01:35 PM
yeah, that all makes sense.
I didnt take into consideration the oil blow, im sure the Z32 MAFS is a bit stronger than the KA MAFS. I hated that thing. I once got a smudge of filter oil on it, and it failed.

killjoy
03-14-2006, 01:36 PM
The only reason i would ever want to do this is simply to have a 4" intake pipe with no reduction for the maf. Though its a little cosmetic, the other things aren't a big deal to me.

forcefedS13
03-14-2006, 01:54 PM
well, i can see the logic in faster spool, and your intake idea should also help with that. I forgot...what size turbo are you going to run?

I checked out your pics, like the car...tht was a steal.

killjoy
03-14-2006, 03:22 PM
I just received my gt3076r .63 with a true Garrett GT30 compressor housing, not the S housing.

luka
03-14-2006, 03:45 PM
I always thought that the problem with taking a factory dsm/nissan maf and going blow-through was that the maf has no way of measuring boost and since it's suppose to be before the turbo it's circuitry assumed atmospheric pressure at all times.

here's a pic of my GM MAF setup on my colt, right where the IC pipe bends down off the throttle body is where it is.

you can see the beginning of the coupler just behind the air filter.

http://static.flickr.com/37/112581695_ce29ed329b.jpg

forcefedS13
03-14-2006, 03:51 PM
But if it was reading atmospheric pressure, it is adding fuel based on those measurements. Whereas the blow-thru design would basically give the ECU "real-time" data so to speak.

Voltron
03-14-2006, 03:58 PM
A MAFS reads airflow. Boost or no boost doesn't matter

forcefedS13
03-14-2006, 04:40 PM
which would make that setup that much more a reason to use.
Its doing the same job it was before, and you get a little more spool out of your turbo.

killjoy
03-14-2006, 05:04 PM
What makes you think that you get faster spool from this?

Transient response, yes, but it doesn't spool earlier to my knowledge.

forcefedS13
03-14-2006, 05:07 PM
no bottle neck at the intake. going from a 3inch inlet to 2inch and back to 3inch.

The Z32 would be the same size.(3inch) so less of a bottle neck.

http://forums.freshalloy.com/ubbthreads/showflat.php?Cat=&Board=UBB9&Number=67990241&page= 0&view=collapsed&sb=5&o=&fpart=1

_Def_
03-14-2006, 05:54 PM
no bottle neck at the intake. going from a 3inch inlet to 2inch and back to 3inch.

The Z32 would be the same size.(3inch) so less of a bottle neck.

http://forums.freshalloy.com/ubbthreads/showflat.php?Cat=&Board=UBB9&Number=67990241&page= 0&view=collapsed&sb=5&o=&fpart=1




It's less of a "bottleneck" because of the lower velocity through it in a blow-thru setup. Higher pressures(and density consequently) = lower velocities for a given massflow by lowering the volumetric flow rate. Basically, you'll get less pressure loss across the MAF. Not to mention you'd ideally want the least amount of pressure loss BEFORE the compressor so that it doesn't get "magnified" by whatever pressure ratio your compressor is operating at(which is a ways higher than 2:1 for most interested in a setup like this).

I'm going to a blow-thru setup sometime in the near future.

luka
03-14-2006, 07:01 PM
But if it was reading atmospheric pressure, it is adding fuel based on those measurements. Whereas the blow-thru design would basically give the ECU "real-time" data so to speak.



what I meant is that a draw-through design has air pressure as a constant in it's calculation of the amount of air passing through.

ie. (grossly simplified) air mass = atmospheric pressure (~14.7psi) x 1/air temp x speed

but in a blow through it's no longer at atsompheric pressure it's 14.7psi+boost so I would think in a draw gone blow, without tuning would run lean.

I could be wrong but that's how I always looked at it.
unless the density of the air has an affect on how well it cools down the plantium element.

I've never taken a nissan MAF apart so I'm not sure exactly what system it uses but I know a DSM maf uses the karmen vortex or whatever it's called.

_Def_
03-14-2006, 08:20 PM
But if it was reading atmospheric pressure, it is adding fuel based on those measurements. Whereas the blow-thru design would basically give the ECU "real-time" data so to speak.



what I meant is that a draw-through design has air pressure as a constant in it's calculation of the amount of air passing through.

ie. (grossly simplified) air mass = atmospheric pressure (~14.7psi) x 1/air temp x speed

but in a blow through it's no longer at atsompheric pressure it's 14.7psi+boost so I would think in a draw gone blow, without tuning would run lean.

I could be wrong but that's how I always looked at it.
unless the density of the air has an affect on how well it cools down the plantium element.

I've never taken a nissan MAF apart so I'm not sure exactly what system it uses but I know a DSM maf uses the karmen vortex or whatever it's called.



You're wrong. Pressure isn't constant in a draw-thru MAF anyway since you will get a pressure drop at higher flowrates. Besides, atmospheric pressure changes by a few tenths of a psi from day to day at the same location due to the weather. I see very accurate digital barometers almost every day and the pressure here(which isn't far above sea level) ranges from about 14.1-14.5 psia.

The MAF measures the MASS of the air going into the engine - PRESSURE DOES NOT MATTER IN THIS MEASUREMENT! I don't know why people have such a hard time seeing this.

S15xedS13
03-14-2006, 09:29 PM
The MAF measures the MASS of the air going into the engine - PRESSURE DOES NOT MATTER IN THIS MEASUREMENT! I don't know why people have such a hard time seeing this.



Thank you.

Nissan MAFS are Hot-Wire type, or Hot-film type. As air flows across this heated wire, it cools, the MAFS goal is to keep that wire at a constant temperature, so it increases the voltage, thus the current through the wire. The MAFS measures this increase in voltage and sends it to the ECU. It is a non-linear function, that is why when you change meters you ahve to re-tune the ECU.

luka
03-15-2006, 06:41 AM
You're wrong. Pressure isn't constant in a draw-thru MAF anyway since you will get a pressure drop at higher flowrates. Besides, atmospheric pressure changes by a few tenths of a psi from day to day at the same location due to the weather. I see very accurate digital barometers almost every day and the pressure here(which isn't far above sea level) ranges from about 14.1-14.5 psia.

The MAF measures the MASS of the air going into the engine - PRESSURE DOES NOT MATTER IN THIS MEASUREMENT! I don't know why people have such a hard time seeing this.



thanks for the clarification.

forcefedS13
03-15-2006, 08:21 AM
So if the MAFS is measuring MASS, then it is really better to put it on the cold pipe in front of the throttle, so it can get an accurate measurement of the mass air that is entering the motor instead of the air drawn thru that sees a loss as it goes thru the IC and is recirculated AFTER the sensor iback into the turbo for compression.

Voltron
03-15-2006, 10:18 AM
I am not sure that it is better
The idea is that moving the MAFS does not change the air/fuel ratios, so its not more or less accurate. If anything I suppose its a more recent measurement, and I don't know wether or not that matters to the engine management.
An intercooler will cause a pressure drop, but it won't change the ammount of air that goes past the MAFS.