Blow-Thru vs Draw-Thru MAF Setups

blown98gt

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I wanted to type this up so that anyone thinking about going Forced Induction (Turbo/Supercharger; Minus Nitrous) knows what the difference is and the benefit of doing one over the other. In the end it's your own opinion and that is that. (this is not meant to persuade you one way or the other just to kind of tell you exactly how each of the types works.

I'm going to start out with a description of what exactly a MAF is and how to works then tell you each of the different types of MAF setups.

MAF
The mass air flow sensor works in conjunction with the oxygen sensor and the engine control system. While the oxygen sensor determines the oxygen levels in the exhaust system, the mass air flow sensor is used to monitor the amount of air passing through the engine while running. A vehicles mass air flow sensor delivers a signal to the ECM (engine control module). There is a small sensing element or "hot wire" (a wire that gets extremely hot to read air molecules) that is used to give electronic feedback to the ECM for processing air partials. The mass air flow sensor is reporting to the ECM how much air is running through the engine. The ECM will then take all the information and adjust the fuel to match the airflow with the oxygen that is being introduced into the motor.

Blow-Thru
A blow-thru setup is one of the two types of MAF setups for a boosted application. In a blow-thru setup the MAF sits AFTER the air in sucked in through your intake pipe. In all most all Turbo applications you will see a blow-thru setup. The MAF usually is placed in either the passenger side fenderwell or in a straight section of pipe going directly to the TB. It's a good rule of thumb to have atleast 5-8'' of pipe in a blow-thru setup that way the air is getting correctly metered. After going Intercooled it's a really good idea to go ahead and switch over to a blow-thru setup. You see there is more plumbing associated from s/tc to the intercooler and then to the TB that cause a much longer time delay between air entering the MAF and actually entering the engine. The air is like a big spring in the intake tract and this cause a larger MAF signal error. In Intercooled setups it's best to have a blow-thru setup so that you can measure air right before it goes into your TB so that you get the correct amount of air. One of the biggest issue is turbulent air caused by the 90 deg elbow before the MAF. This makes the a/f choppier. It can vary as much as .6-.8 points during a WOT run. So like I stated before the MAF should be in a straight section of pipe not in a bend, or right before a bend. In a blow-thru setup you'll have the option to either use a BOV or a BPV since the air is metered in the fenderwell or AFTER the inlet of the s/tc you have the option to run a vented BOV or BPV before the MAF. Unmetered air can be vented into the Atmosphere.

Benefits of Blow-Thru setup
Vent into the Atmosphere
Air that is being metered does not have to travel as far causing a spring like effect in the intake tract givng you MAF signal errors or surges.
You can run a big power pipe without having to funnel down for the MAF (which defeats the purpose of having a power pipe)
Less distance between the throttle body and mass air meter means better response. Less pinging when shifting

Draw-Thru
A Draw-thru setup is actually a very simple setup where the MAF is on the end of the inlet pipe of the s/tc (not seen on most turbo applications) The air is metered right when it is sucked in to the inlet pipe. This is how most/all cars from the factor come. Even 03/04 cobras as a draw-thru setup and the MAF sits on the intake pipe going to the s/c. In a Draw-thru setup you CAN NOT run a BOV (EXCEPTION RULE: Some BOV offer a recirculation piece that goes on them this take a bov and makes it a bpv) in a Draw-thru setup the air is metered from the moment that it enters even before the S/C so the air has to be recirculated and vented back into the inlet pipe before the S/C and after the MAF. All Vortech S/C kits come as a Draw-Thru setup.

Benefits of Draw-Thru setup
You recirculate the BPV into the intake and it's much quieter than a BOV
Some say a more accurate MAF reading

Converting Blo-thru to Dra-thru
You relocate your MAF before the head unit, so where ever it pulls the air from, is where your MAF goes. Now in order to get good driveabilty and not have the EEC get mad at you by venting your bypass to atmosphere, you need to recirculate the bypass AFTER the MAF and before the headunit. I the way procharger has the stock inlet setup, you can do that without any mods with the stock bypass...the only thing you are going to have rig up, that is assuming you have the stock inlet, is getting the MAF onto the inlet hose.

BOV VS BPV
(Blow Off Valve / Bypass Valve)
A Blow off valve dumps compressed air to the atmosphere when the throttle is lifted.
A blow off valve vents the hot air into the atmosphere
A Bypass valve usually passes air a BOV would dissipate to the atmosphere back into the intake track after the MAF and before the inlet of the turbo.
A Bypass Valve can be used as a BOV on a Blow through, dump to atmosphere design.
A bypass valve releases 200 degree air back into the mouth of your S/Tc
The general purpose of both is to prevent compressor surge.

Blow-Thru MAF's

PMAS 3'' Pro Tube Blow-Thru MAF
- This is a very common Blow-thru MAF and a lot of people seem to use it, it utilizes a PMAS Maf and requires the MAF to be programmed for you injectors size, s/c vs n/a, and also vehicle specific (as all blow-thru must, this is something that a tuner can do, but will be set upon purchase of one)
- http://www.mperacing.com/maf.html

Lightning 90mm MAF
- People have been using the Lightning MAF in their blow-thru setups, it's a very common and probably cheapest route to go with going blow-thru. Only down fall is that the unit goes from a 3'' to 4'' (an adapter is used) which can cause issues vs just having a 3'' tube with MAF flange and MAF in it.
- http://modularspeed.com/90limaf5.html

SCT BA2800
- Yet another good blow-thru MAF that is used widely. The SCT Ba2800 can support up to 800hp.

75mm Blow-thru w/PMAS HPX MAF
-I recommend using this for your blow-thru setup. It does require the adapter cord but can support up to 800 hp without having to use a MAF extender. best bang for the bucks and overall great quality.
-This unit uses a 360 deg. MAF sensor to make sure that total air is read properly.
- http://modularspeed.com/75blthwpmhpx.html

Abaco DBX Performance MAF
- It's a newer MAF to the market and through my tuner i've heard mixed reviews some people have great luck with this and some people don't, I don't know a whole lot about this unit so I can't really go in depth into it but from what i've seen it has a lot of advantages for tuners.
-DBX? is a state of the art multi sensor digital mass air meter with multiple design & functionality patents pending. DBX? multi sensor design allows the DBX? mass air meters to be installed in any configuration to the throttle body at any clock rotation with little to no signal deterioration.
-DBX's? digital design allows the consumer to choose from up to 10 different mass air calibrations by the turn of a switch. In addition, these calibrations can be changed easily with our free software by plugging into the USB port. The DBX? is fully programmable so that make, year, and model applications are simply handled by wire harness plug design. This makes the DBX? mass air meter's applications virtually endless.
- http://mustang.c-f-m.com/index.asp?PageAction=VIEWPROD&ProdID=2003

Custom Blow-thru MAF
- To me I think this might be the best route to go, It is a lot easier to make a blow-thru MAF than everyone thinks. As stated above you need atleast 5-8'' of STRAIGHT pipe, then you need a MAF flange these can be purchased online and pretty cheap. Since the '05 Mustang GT MAF seems to be tuners choice for blow-thru applications I'd recommend using this, and you'll need an adapter to make it work for the SN95 but for approx $315 you can purchase the entire unit stated in just the previous MAF.
- http://modularspeed.com/mafsepa.html
- http://modularspeed.com/mafflanges.html

Draw-Thru MAF

PMAS Velocity MAF
- Just a standard Draw-Thru MAF
- http://www.mperacing.com/maf.html

90MM Lightning MAF
- Yes the Lightning MAF is normally used as a draw-thru MAF it has a 4'' inlet (which your filter screws onto, and then sizes down to a 3'' for your pipe) The Lightning MAF is a good upgrade for a draw thru MAF and is good up to 450 hp anything over a MAF Extender (Such as a Diablo MAFia is needed)
- http://modularspeed.com/90limaf5.html

SCTBAXXXX
- The Sct BA (Big Air Series) is a very reliable and highly used draw-thru MAF.
- The BA2600 can support around 700 rwhp (sct site HP numbers)
- The BA3000 can support up to 825 rwhp (sct site HP numbers)
- http://www.sctflash.com/BigAir.php

I understand there are tons of MAF's and MAF companies i've just tried to highlight a few major ones and hit some of the key points for them.

(I will periodically update this as I see fit or if I find more information out that seems valid, or if it needs to be corrected.)
 

Dalamar

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Re: Blow-Thru vs Draw-Thru Setup

Great info!
I have a draw through on my setup.

Stickey.
 
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blown98gt

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Re: Blow-Thru vs Draw-Thru Setup

Thanks, I was bored after PT this morning so I figured the question is thrown around enough that it wouldn't hurt to have a write up on each one. It's hard to say the pros and cons for each because that seems to be more opinion based than fact based. I just hope that people who want to go s/tc can look at this and better understand there kit how it's setup and different setup routes.

I myself have a blow-thru and i'm using a 75mm Blow Through w/ PMAS HPX MAF from Modularspeed.com which is good all the way to 800 hp. It uses a 360 "hot wire" which reads the air a lot better. There is tons of things on choosing the right MAF for a blow/draw-thru setup which can play a role too.

Thanks for making this a sticky
 

CC'S95GT

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Re: Blow-Thru vs Draw-Thru Setup

good write up. it might also help if it said MAF in the title too.
 
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blown98gt

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changed lol...

I think I did this more so because I get tired of hearing that "can i run a bov on my vortech kit" question lol
 

mikey94gt

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One bit of info to add, put the MAF in the pipe so that it has a straight piece of pipe that is twice the diameter of the pipe long, then it will get a good reading, no matter if it is draw through, blow through, NA, whatever. This is from Cartech book Engine Management, Advanced Tuning, by Greg Banish.
 
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blown98gt

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I had put it's a good rule of thumb to have 5-8'' of pipe for a blow thru MAF 3'' dia = 6'' long pipe. Most blow thru pipes you buy are 8'' long :)
 
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blown98gt

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way back when, I had this question and everyone always answered blow-thru means bov and draw-thru means bpv but no one really elaborated on it so I did some research and read a lot. My tuner actually told me how a MAF works because mine got wet with meth and got ruined and so I just pulled all I knew together, but if anyone of it is not correct i'm sure someone will let me know :)
 

mikey94gt

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Your good, it checks out with the book I quoted in my last post.
 
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blown98gt

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Updated on a few common Blow-Thru MAF's and i'll be updating later tonight some common Draw-thru MAF's that are commonly used.
 

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