# Why 4" MAF on 12v VR6



## DaKRUSH (Jan 9, 2007)

Curious to why most fueling kits and turbo kits come with a 4" MAF housing? I see the obvious is air flow, but say your running a turbo with a 2,5" inducer, do you need a 4" housing for the software to act properly. The only reason im asking because i tend to see a lot of trends happen because its what everyone else is doing on the forums. So basically im asking for the scientific reason for the 4" housing.
Thanks in advance.
any response/bump is welcome


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## vr6freak (Apr 4, 2003)

*Re: Why 4" MAF on 12v VR6 (DaKRUSH)*

yes.
because that is the way the software is written


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## DaKRUSH (Jan 9, 2007)

*Re: Why 4" MAF on 12v VR6 (vr6freak)*

Do you know how much of a difference the air flow is between a stock housing and a 4" housing, And also has anyone compared different sizes? i mean im sure the more flow the better but how much better is the 4" over a smaller size. If there is a big difference then why isn't everyone running 5"or bigger..


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## PjS860ct (Dec 22, 2002)

*Re: Why 4" MAF on 12v VR6 (DaKRUSH)*

PM Jefnes3, the tuner that wrote the software 


_Modified by PjS860ct at 1:21 AM 11-29-2008_


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## jettaglx91 (Jul 27, 2004)

*Re: Why 4" MAF on 12v VR6 (DaKRUSH)*

for the most part i believe it has to do with not maxing out the voltage reading in the stock maf size housing.
back in the day before c2 had their setup the only way really was a rise to rate regulator which basically just dumped crazy fuel on the onset of boost to keep things safe but with huge drivability drawbacks. 
the increased maf size isnt uncommon just that the vr6 is the largest, for instance most of the 4cylinder apps upgrade to the vr6 sized housing


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## DaKRUSH (Jan 9, 2007)

*Re: Why 4" MAF on 12v VR6 (jettaglx91)*

thanks for the responses, i tried searching for jeffnes's name but got nothing, Voltage makes a lot of sense i didn't think of that. thanks again im going to call c2 and im sure they can answer my questions. 
The only reason i ask is because do to inspections and what not its becoming harder to put whatever you want on your car, so im going to build a "stock" looking vr6 turbo and i am going to try to retain stock air box and MAF. im sure someone has done this.


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## KubotaPowered (Jan 27, 2005)

*Re: Why 4" MAF on 12v VR6 (DaKRUSH)*

Air flows faster through the stock MAF maxing it out faster. If you rewrite the software to see the smaller voltage delta over the same RPM/load as the the stock tune and MAF you can flow more air without going static on the meter too soon. Think of a river, it you take a river and push the banks together the water moves really fast, take the banks and widen them and with the same volume of water it is now moving slower, same thing applies here, this way all the air can be metered accurately




_Modified by KubotaPowered at 11:42 PM 11-28-2008_


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## ade007 (Jun 12, 2007)

4 inch maf is to fool vw stock software to allow it to run larger injectors . i think the stock maf and stock software will run up 30lb injectors before it reaches it adjustment limit. i ran 42lb injectors for 12 months with stock ecu software just a larger maf obd1 vr6


_Modified by ade007 at 1:16 PM 11-29-2008_


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## DaKRUSH (Jan 9, 2007)

*Re: (ade007)*

Ok thanks for the very informative answer i really appreciate it. I understand how it works now http://****************.com/smile/emthup.gif


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## Jefnes3 (Aug 17, 2001)

*Re: (ade007)*

Why a larger houisng:
Stock VR6 MAF maxes out around ~280-300whp.
4" housing maxes out in the mid 400's whp.
-Jeffrey Atwood


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## slc92 (Feb 9, 2005)

*Re: (Jefnes3)*


_Quote, originally posted by *Jefnes3* »_
Stock VR6 MAF maxes out around ~280-300whp.


Very true. Unfortunately, I prove this every time I hit 9psi and it's really cold out







MAF hits 5V and the car hits fuel cut.


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## ade007 (Jun 12, 2007)

*Re: (slc92)*

av you tryed a larger maf housing ?? with 280 300 whp with stock maf 5v limit id guess ur near the limit of the 30lb injectors anyway what turbo and cams are you running ?


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## ade007 (Jun 12, 2007)

*Re: (Jefnes3)*

re 4" housing maxes out in the mid 400's whp.
so a 4.25" (108mm) housing will allow to run 550cc injectors and max out in the mid 500 whp










_Modified by ade007 at 8:39 AM 11-30-2008_


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## VR6rocks (Jun 5, 2004)

*Re: (ade007)*


_Quote, originally posted by *ade007* »_av you tryed a larger maf housing ?? with 280 300 whp with stock maf 5v limit id guess ur near the limit of the 30lb injectors anyway what turbo and cams are you running ? 

slc, be careful when doing this, you'll be scaling down your sensor readings and running leaner than you're used to.


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## 16V4LIFE (Sep 29, 2004)

*Re: (VR6rocks)*

I have not seen 1 decent explaination so far. Picture a 1" diameter housing (Theoretically if the sensor could fit in that housing), and picture the velocity of air that would be travelling past the sensor at 3000RPM at medium load. It would be insane! The sensor can only accurately detect a velocity of air within certain parameters. The larger the housing is, the more air you can flow through the housing/sensor combo with out maxing out the stock sensor, as only a pecentage of the flow actually goes through the sensor. The smaller the housing, the higher percentage of the total air volume will go through the sensor itself. And the larger the housing, the less likely the sensor is to get maxxed out. This allows them to retain the stock sensor, without having to make an expensive aftermarket sensor jacking the price of the kit to astronomical levels. Hope this was helpful.


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## jettaglx91 (Jul 27, 2004)

*Re: (16V4LIFE)*

it doesnt have to be quite so technical as most people wouldnt understand it anyway
the answer jefnes3 gave is a simple and to the point and he knows what he is talking about lol


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## slc92 (Feb 9, 2005)

*Re: (ade007)*


_Quote, originally posted by *ade007* »_av you tryed a larger maf housing ?? with 280 300 whp with stock maf 5v limit id guess ur near the limit of the 30lb injectors anyway what turbo and cams are you running ? 

No, b/c the chip is tuned for the stock MAF housing. Bigger housing would have to be custom made then alot of time spent with a MAF controller/piggyback. Just not worth it for ~20whp until the inj. max. I have considered a rising rate fpr though at the point the MAF max's on up.
Setup is a full t4 60trim/.69 A/R Ptrim, dsr 256 cams, 3"DP to 2.5" no cat, ported head, ported ATP manifold, intercooled.


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## slc92 (Feb 9, 2005)

*Re: (jettaglx91)*


_Quote, originally posted by *jettaglx91* »_it doesnt have to be quite so technical as most people wouldnt understand it anyway
the answer jefnes3 gave is a simple and to the point and he knows what he is talking about lol

Agreed. Chip was tuned for a certain MAF housing/injector. They max at 5V and your car will hit fuel cut and/or no longer add fuel as you flow more air.


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## ade007 (Jun 12, 2007)

*Re: (slc92)*

id recomend reading this old post before c2 started selling it explains details http://forums.vwvortex.com/zerothread?id=157169 then get yourself a 95mm internal diameter maf housing some 36lb injectors with stock obd1 4 bar fuel reg then tell us its tuned for the stock housing . ive tryed with a modified hotwire maf type i had to grind it apart and silicon bond it into the larger tube and it ran sweet idle was perfect like stock injectors pulled clean to the rev limit with no hicups


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## slc92 (Feb 9, 2005)

*Re: (ade007)*

Thanks. Very interesting. I'm gonna read the whole thing now.
The 30# chip is tuned for the stock housing and Bosch 30# redtops. If it can be modded to "work" with a bigger housing/inj then I'll







 to that http://****************.com/smile/emthup.gif 
Just to be clear, you are saying that you built a custom 95mm MAF housing for a Corrado one piece MAF, put in 36# inj., stock 4 bar FPR, and the car ran fine with a 30# chip?


_Modified by slc92 at 12:28 PM 11-30-2008_


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## slc92 (Feb 9, 2005)

*Re: (slc92)*

Quote from the same guy that you quoted two years later
"Sure does.... a larger housing increases the sensors range.
It will not make 'performance' changes by itself, i.e. slap it on 
an NA car and you can expect ZERO gain. It does allow
proper measurement of increased airflow when you add some boost.
"*You can 'slap' it on with matching injectors, but your car will run
CRAPPY. a Re-map is needed to bring all back to 'normal'."*
I still wouldn't expect a car to run right by installing a larger housing and injectors. Might get you close though.


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## 16V4LIFE (Sep 29, 2004)

*Re: (jettaglx91)*


_Quote, originally posted by *jettaglx91* »_it doesnt have to be quite so technical as most people wouldnt understand it anyway
the answer jefnes3 gave is a simple and to the point and he knows what he is talking about lol

It was simple and to the point, but in no way answered what is being asked. I know that he knows what he is talking about, but it doesn't really answer why the reason for bigger maf housing. Should I just not answer the OP's question because the answer might be too technical for some people (Even though I think I explaqined it pretty well in easy to understand laymans terms)? The OP knows that the higher horsepower cars are using the bigger MAF housing, but specifically asked why. So I answered it with an actual explaination.


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## ade007 (Jun 12, 2007)

*Re: (slc92)*

re:Just to be clear, you are saying that you built a custom 95mm MAF housing for a Corrado one piece MAF, put in 36# inj., stock 4 bar FPR, and the car ran fine with a 30# chip?
i had 36# injectors the early one piece hotwire type maf modified into a 95mm id housing stock obd1 4bar fpr and a stock chip ran perfect


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## adaptorman (Dec 12, 2007)

*Re: (ade007)*

is it one of these types he needs


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## ade007 (Jun 12, 2007)

that was mine


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## DaKRUSH (Jan 9, 2007)

*Re: (ade007)*

What it sounds like from most alll the responses, is, its not the amount of air that the turbo is sucking in but rather the amount of air the Sensor can actually process that is the reason for the larger housing. 
So has anyone done or know of anyone that has spaced there sensor out of the housing, so basically only half of the sensor is actually in the housing or would you still have the same problem of having the sensor being worked to its max because the air is still traveling through too fast?


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## groupracer (Apr 15, 2002)

*Re: Why 4" MAF on 12v VR6 (DaKRUSH)*

First off, I hope my math is right....
Ok, so a 3” MAF has an approx cross sectional area of 28.27 sq in. The 4” MAF has an approx cross sectional area of 50.26 sq in. Nearly double the area!! A 1” diameter increase has almost doubled the area, amazing, isn't it? That's an increase of almost 22 sq in, or about 77%!! Therefore given what the maximum read flow of a stock sensor (whatever that is, I don't know) I'm sure the sensor was never meant to read that much air, so you have to “trick” the sensor into thinking it’s flowing much less air than it actually is by increasing the flow area, slowing down the air with the 4” MAF relative to a 3” MAF, and compensate the required fuel delivery with software to deal with the new flow requirements.
So, in this scenario if you have a turbo'd engine (it can be a N/A too) that say needs 1000cfm (28,800 ci/sec!) and you have a 4” MAF, it will have an approx air velocity, at max, of 573”/sec, Most likely within the range of the stock sensor, while that 3” MAF will have an air velocity, at max, will be approx 1018”/sec, most likely, beyond the range of the stock sensor!
Remember, the sensor itself only shows a relative voltage output. It is heated to a high temperature (I seem to remember something like 5000 deg F), and as it’s cooled by the air flow, its resistance changes and so it goes the relative voltage that flows through it. It doesn't care what the velocity of the air is. Only a given amount of air will output a given voltage and that relative difference is what matters. A given velocity (or flow of air) will make it show a certain voltage output no matter what the size of the MAF is. It is up to the computer and its programmed map that says how much fuel is necessary for a given voltage change related to the flow of air. 
I hope this helps too... http://****************.com/smile/emthup.gif


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## Noobercorn (Aug 17, 2007)

*Re: (slc92)*


_Quote, originally posted by *slc92* »_
I still wouldn't expect a car to run right by installing a larger housing and injectors. Might get you close though.


did this on an A4, and it worked.


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## ade007 (Jun 12, 2007)

*Re: (VR6rocks)*


_Quote, originally posted by *VR6rocks* »_
slc, be careful when doing this, you'll be scaling down your sensor readings and running leaner than you're used to.

yes larger maf housing = run lean 
larger injectors =run rich 
larger injector + larger maf housing size matched within +/- 25% ecu fuel trim corrections = run ok


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## DaKRUSH (Jan 9, 2007)

*Re: (ade007)*

great responses guys, very informative http://****************.com/smile/emthup.gif


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## TBT-Syncro (Apr 28, 2001)

*Re: (ade007)*


_Quote, originally posted by *ade007* »_
larger injector + larger maf housing size matched within +/- 25% ecu fuel trim corrections = run ok 


just keep in mind that you dont have ecu fuel trims while under boost, only while cruising.


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## CorradoMagic (Apr 11, 2008)

so, on a Corrado with 30# tune, 6 pin MAF wire in a new 4" husing, it was run lean using the chip pspecified 30# injectors.
But.. If you changed to 36# injectors it would get more fueling.
Is theory accurate? Would it work,, corectly?
After ethe ECU adjusts fuel trims (max around 25% adjustment?), would it work to deliver the additional needed fuel and not max out the 5v limit while still providing an ideal AF ratio?
TBT- the ecu wont trim fuel under boost, is that due to WOT/o2 loop? 
Would really like to get this sorted. I see max inj. # load limits of 3" all too often, way too soon. 


_Modified by CorradoMagic at 4:11 PM 12-4-2008_


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## Noobercorn (Aug 17, 2007)

*Re: (CorradoMagic)*

keith, if you have a 4 pin MAF, that is not a standard corrado tune. 
however, your theory SHOULD work, but would require and AFPR to dial it in at idle. 
WOT on C2 stuff is indeed ignoring O2, thus the AFPR also.


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## ade007 (Jun 12, 2007)

*Re: (TBT-Syncro)*


_Quote, originally posted by *TBT-Syncro* »_
just keep in mind that you dont have ecu fuel trims while under boost, only while cruising.

here is jefnes3 words 
I KNOW that the MAF is used by the ECU all the time, one exception,
when its broken/disconnected. I have logs of this too. Change the MAF signal and
the injector pulse width is changed at any throttle position and RPM
at wot in boost the maf will register the amount of airflow the engine is taking in and tell the ecu to alter the injector open close time


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## TBT-Syncro (Apr 28, 2001)

*Re: (ade007)*


_Quote, originally posted by *ade007* »_
here is jefnes3 words 
I KNOW that the MAF is used by the ECU all the time, one exception,
when its broken/disconnected. I have logs of this too. Change the MAF signal and
the injector pulse width is changed at any throttle position and RPM
at wot in boost the maf will register the amount of airflow the engine is taking in and tell the ecu to alter the injector open close time 

yes. you still have maf/tps maps, but they dont have trims.







so if you're running larger injectors, smaller housing, etc, etc, the ecu can NOT compensate while under boost.


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## CorradoMagic (Apr 11, 2008)

*Re: (Noobercorn)*


_Quote, originally posted by *Noobercorn* »_keith, if you have a 4 pin MAF, that is not a standard corrado tune. 
however, your theory SHOULD work, but would require and AFPR to dial it in at idle. 
WOT on C2 stuff is indeed ignoring O2, thus the AFPR also. 

whoops. I meant 6 pin Corrado (3") MAF, I'll edit that.


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## ade007 (Jun 12, 2007)

while under boost the maf is metering more air more being intaken into the engine so the voltage on the maf curve will be higher and the ecu will alter the injector opening closing times for more fuel to compensate for the extra air being metered while in boost or not


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## Noobercorn (Aug 17, 2007)

*Re: (CorradoMagic)*


_Quote, originally posted by *CorradoMagic* »_so, on a Corrado with 30# tune, 6 pin MAF wire in a new 4" husing, it was run lean using the chip pspecified 30# injectors.
But.. If you changed to 36# injectors it would get more fueling.

plop in 36#'ers and an AFPR and see how she does.








if you have a 4" MAF on a 30# tune, you need more fuel!!!!! (mathematically speaking)


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## ade007 (Jun 12, 2007)

im unsure whats been altered on the 30# tune it may have had the pulse widths reduced by a percentage to work with the stock size maf if this is so id guess ud need even bigger than 36# injectors if this is the case best to have a wideband and an inline walbro if going over 280whp and take it easy 


_Modified by ade007 at 9:50 PM 12-4-2008_


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## CorradoMagic (Apr 11, 2008)

what I have is 
30# inj.
30# custom tune
4 bar FPR
Corrado ECU & OEM 3" MAF
thinking the 4" housing w/ 6pin Rado MAF & 36# inj. would help.
(just keeping what I have & what I think could help clear)


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## slc92 (Feb 9, 2005)

*Re: (CorradoMagic)*

Interesting discussion. I have a spare MAF(internals anyway) so the custom larger MAF wouldn't be that much $$. Size the injectors and MAF housing as close as possible and then run a MAF controller(Apexi) etc. and tune it with the wideband. I wonder if it would work.








Anyone know what the inner diameter of the Corrado MAF is? I did a rough measurement and it's ~ 75 mm. What size MAF would I need to run 36# or 42# inj. andd keep things proportional?
30#= 315cc
36#= 380cc
42#= 440cc


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## slc92 (Feb 9, 2005)

*Re: (ade007)*


_Quote, originally posted by *ade007* »_
i had 36# injectors the early one piece hotwire type maf modified into a 95mm id housing stock obd1 4bar fpr and a stock chip ran perfect 


OK, stock chip. This makes sense according to those early equations from the link you posted. 19# inj to 36# inj = ~3inMAF to 4 in.
I'm running a 30# chip though. I think a ~3.5in MAF should get me close w/ 42# maybe?


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## DumbGTI (Nov 30, 2008)

*Re: (slc92)*

I wish we didn't have to run a MAF. http://****************.com/smile/emthdown.gif


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## ade007 (Jun 12, 2007)

*Re: (slc92)*

remember when doing calcs that 
30#= 315cc = 363cc 34lb @4bar
36#= 380cc = 438cc 41.7lb @4bar
42#= 440cc  = 508cc 48.3lb @4bar 

so if 95mm id maf works with 36# injector stock chip @4bar there is no reason why it will not be same with 42# injectors @3bar



_Modified by ade007 at 3:13 PM 12-5-2008_


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## Noobercorn (Aug 17, 2007)

*Re: (CorradoMagic)*


_Quote, originally posted by *CorradoMagic* »_what I have is 
30# inj.
30# custom tune

what makes your 30# tune different than the others? that may dictate the difference with larger inj & MAF


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## CorradoMagic (Apr 11, 2008)

*Re: (Noobercorn)*


_Quote, originally posted by *Noobercorn* »_
what makes your 30# tune different than the others? that may dictate the difference with larger inj & MAF

I have: 
what I have is 
30# inj.
30# custom tune
4 bar FPR
Corrado ECU & OEM 3" MAF
I guess only Jeff would know. I am running the 262's & a MK4 HG, so I'm would think timing was adjusted (retard) as well as inj. duty cycle. I was told I am at the limit of what the 30# can feed.
It was estimated I picked up another 20-25hp with the tune.... thats great and all, but its still not 100%


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## Noobercorn (Aug 17, 2007)

*Re: (CorradoMagic)*


_Quote, originally posted by *CorradoMagic* »_
I have: 
what I have is 
30# inj.
30# custom tune
4 bar FPR
Corrado ECU & OEM 3" MAF 

i ran all that on my 92, with 256's and a stock HG. i wonder what is really seperating the two of us. 
i was running 15psi with LOTS of meth tho.


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## CorradoMagic (Apr 11, 2008)

coilpack. slightly raised CR (debatable)
Werent the Dizzy originally 42# ?
Coils were 30#


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## Noobercorn (Aug 17, 2007)

*Re: (CorradoMagic)*

nah, dizzy and coil bof 30#. and a little known secret, the tunes are the same








still, you should be able to run more fuel wwith a larger MAF, AFPR, and larger INJ. 
hell, EIP did it for years.


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## CorradoMagic (Apr 11, 2008)

the only thing about the AFPR is that the rest of the tune/drivability is outa wack, right? 
IIRC Noah has done the AFPR w/ C2 chip, not sure about INJ. tho.


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## Noobercorn (Aug 17, 2007)

*Re: (CorradoMagic)*


_Quote, originally posted by *CorradoMagic* »_the only thing about the AFPR is that the rest of the tune/drivability is outa wack, right? 
IIRC Noah has done the AFPR w/ C2 chip, not sure about INJ. tho. 

once set at idle, it should raise 1:1 under load.


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## ade007 (Jun 12, 2007)

*Re: (CorradoMagic)*


_Quote, originally posted by *CorradoMagic* »_the only thing about the AFPR is that the rest of the tune/drivability is outa wack, right? 
IIRC Noah has done the AFPR w/ C2 chip, not sure about INJ. tho. 

afpr will just alter the base pressure injectors making them like variable larger or smaller in size but a rising rate type would throw things outa wack


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## CorradoMagic (Apr 11, 2008)

lets keep the good info coming.


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## NeonGreenbangbang (Dec 20, 2008)

*Re: (CorradoMagic)*

Ohhhh, this is scary assuming I have what is being said correctly. So, the larger housing is being used because the MAF pegs at what? 428 grams? So then a larger housing is being used to make the MAF think less air is flowing through it (lower voltage = lower airflow calc). We are now lying to the ECM through it's critical load metering device. However, nobody has addressed cutting the resolution of the MAF input for the fueling and spark tables. The only way this can work and keep the system within its design limits is to alter the effective resolution for the MAF, otherwise there's got to be some other "Lying" that is being done in the prom and that's something that's likely pretty important to know.
Calling Jeff: Please come back into this thread. 

For others, quick example of resolution.
LAirflow is metered in grams per second. Totally hypothetically let's say .5 volts = 100 grams a second, and .51 volts = 102 grams a second in factory conditions. If the MAF output was .505 volts what would the airflow be? 101 grams per second. That's resolution - the fineness of the degree that a measurement can be calculated. Let's say we cut our resolution in half to extent the upper limit of the maximum possible airflow. 100 grams per second would now be .25 volts, and 102 grams per second would now be .2505 grams per second - but there's a problem there, because most ecm's don't calculate out 4 digits past the whole number. Normally they only calculate 2 digits past the whole number in my experience with other ECM's. Therefore *both* 100 and 102 grams per second would look like .25 volts to the ecm. That's the downside of cutting the resolution in half - the precision is literally cut in half. That's still a fixable situation by also adjusting the other load elements for other tables but I think jeff is going to have to chime in here because if that's not done I personally wouldn't be comfortable running that prom with a larger housing. The car may appear to run fine, but the ECM will be outside of it's inital design limits for calculations other than pure airflow.


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## NeonGreenbangbang (Dec 20, 2008)

*Re: (NeonGreenbangbang)*

I left and thought about it some and realized I may not have given you guys a clear cut reason as to why I see this as begin problematic.
Let's say you have a 2.5 inch MAF for an ABA and you use 30lb injectors. Then you go to a 3 inch housing and use 42 lb injectors. You are mechanically reducing the MAF resolution, which as far as fueling goes under WOT, might be okay at best if the injectors provided the exact same increase in fuel delivery that was equal the decrease in resolution from the MAF input. 
2.5" maf = 19.6" surface area (30lb units)
3.0" maf = 28.27" surface area (42lb units)
There is a 31% difference in MAF surface area, and a 29% difference in Fuel Injector Size. That's pretty close, enough that short and long term fuel trim shoudl correct the A/F ratio at idle. 
Why i see a potential problem is that I fear that not all size comparisons are as close, and this does nothing to accounting for things like pump shot, lean cruise, decel/accel lean and enrichment values, etc. It seems like that fueling solution would only really work out for WOT. I really would like to hear more from Jeff about how he's working out those issues..... unless it some "Super Classified Secret."


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## slc92 (Feb 9, 2005)

*Re: (NeonGreenbangbang)*

Taken from another thread. I would be interested to know your thoughts on this. As for Jeff, umm he does this for a living so not sure if he's going to help people bypass his services which I don't blame him for.
If the Corrado MAF is indeed 70mm ID(2.75") then I come up with a 83mm (3.25") housing as being proportional when going from 30# to 42# inj.
Jeffs calcs.
new MAF=old maf x sqrt (new inj/old inj)
= 70mm xsqrt(42/30)
=* 82.83mm*
Another one I found that deals with the % increase
increase%= (diameter of new MAF/diameter of old MAF)squared-1) x100
= (*83*/70)sq-1) x 100
=*40.6%* increase
injector size= (42#-30#)/30#= *40%* increase
Basically a 3.25" MAF has 40% more area than a 2.75" MAF. 42# inj. flow 40% more than 30# inj. I have no idea if this is correct but at least I found two equations that agree I wonder if it would work.


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## Jefnes3 (Aug 17, 2001)

*Re: (slc92)*

All the theory here is basically correct, with an exception or two...
The MAF and ANY fuel injection has non-linear reponse.
These need to be 'tuned' around.
The shorter inj. pulse the more lon lineaar inj. response gets.
Hence, why I tend be VERY specific about how which components are
used with my software.
Practical issues: The 6-pin MAf sensor in the non golf/jetta obd1 cars
is difficult to remove ~safely.

Hold tight, gentlemen (and ladies).
I have a new product in the works that will allow you to sort these issues yourself. The hardware is in design now.
-Jeff


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## slc92 (Feb 9, 2005)

*Re: (Jefnes3)*

Thanks for the heads up. I didn't think it would be that easy.


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## NeonGreenbangbang (Dec 20, 2008)

*Re: (Jefnes3)*


_Quote, originally posted by *Jefnes3* »_The shorter inj. pulse the more lon lineaar inj. response gets.

Very good, that's exactly what I was looking for you to say. http://****************.com/smile/emthup.gif http://****************.com/smile/emthup.gif I didn't really want to go there untill you had a chance to reply, but if you are aware of how small variences in fuel rail pressure can affect the output of an injector pre-opening, just after opening, full open, and closing then that's what I was really going after other than my concerns about the other vehicle management characteristics. However, I now have a bit more faith that you understand those dynamics as well. I don't need them explained to me as far as how you go about working with and around those problems; I know how I've done it and I doubt our approaches are significantly different. I just wanted to see some acknowledgement that there's more to fueling than a mechanical decrease in MAF resolution as an end all to getting large injectors to idle properly. 
Ever consider a dynamically variable fuel pressure regulator as an assistant for something larger than 42lb units in the 4 cyl aba and aba16vt cars? GM has used them with much success.


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## slc92 (Feb 9, 2005)

*Re: (NeonGreenbangbang)*

^
Just to be clear. I don't think anyone here was implying that a vehicle will run as a "tuned" vehicle would by simply popping in larger injectors and a larger MAF housing. I'm not an engineer or tuner and don't pretend to be.
With no other plug and play solution would I give it a shot for a few hundred dollars? Absolutely. Not sure how well it would work but some people tune cars solely w/ a piggyback setup so I don't think it's a stretch to think that the car could be made to run w/ a bigger MAF, bigger inj., and a way to fine tune things (MAF controller and wideband).
From Jeff's post it seems there is still a "solution" in the works so I'll see how that turns out before I proceed w/ any "experimenting".


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## NeonGreenbangbang (Dec 20, 2008)

*Re: (slc92)*

Well, really there is two solutions that already exists to get a car to idle and still supply enough fuel for big power applications. Since I don't know the scale for the flow limit of the stock ecm for VW applications, I can't really say what the specifics of either setup would be if the MAF is still the limiting factor. However, running extra injectors is a simple solution and easy as cake to tune. You can even run it completely independantly and use a MAP to begin running the fuel table just before you reach zero manifold vac. (IE, right before boost). The second is the already mentioned dynamic variable rate fuel pressure regulator. It's similar to an FMU except it lowers fuel pressure at idle instead of the FMU which increases pressure in boost. However it doesn't lower the pressure to the extreme that an FMU can raise pressure, so don't think of it as a big and inprecise, unaccurate fuel leaker. Normally they work for an adjustable 5-8 PSI decrease at idle which is normally substantial enough to get a very large injector to use it's minimum pulse width and still not over-richen the mixture. GM had to use it in factory big block applications with TBI (and CPFI), as TBI is a fueling nightmere. I wish I could reclaim the 2 years I spent messing around with TBI and fueling issues








As far as the other part about being a "tuned" vehicle... having written my own prom's for years and helping other's with their fueling/ignition problems I have seen my fair share of less than perfect work. You can take this for what it's worth, but just because a car is running in a stable condition doesn't mean that's it's properly tuned with a margin of safety and within the managements design limits. I've seen resolutions scaled down and the car ran GREAT! Smooth at part throttle, idled like a charm, and ran like a demon. Except one day a subroutine was commanded and because the ECM was operating based on false input, motors have been popped. The more you lie to your ECM the more you have to alter other elements of it's operation and normally, not for the better. It's one thing to lie to the ECM on target o2 voltage to help richen the car at all times (not to lean it), but when the resolution of a MAF or MAP is altered I get very inquisitive. That's your primary load metering device that you are now spoofing. That's damagerous unless every single map that depends on that voltage is scaled up or down with it. Unless I'm the one looking at the maps.... I'm not sure I'd trust it completely without asking some questions.....


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## slc92 (Feb 9, 2005)

*Re: (NeonGreenbangbang)*

Thanks for your incite. I understand most of what you are saying. I'm in essence "tricking" the MAF but not changing any other inputs/outputs. 
The car does have a wideband and knock control as it would still be running off of the stock Bosch ecu w/ C2 chip.. As long as boost was kept within reason for a specific compression ratio and A/F was proper under boost (11-12.5:1) how exactly could the motor "pop"? What do you mean by subroutine.?

I'm just trying to understand.


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## slc92 (Feb 9, 2005)

*Re: (slc92)*

Cxracing's 3.5" (89mm) pipe is 3mm thick. That means an *83mm *I.D.







I'm dying to try this w/ the 42#'s. If I can find a spare MAF I think I will. If it doesn't work I'm out $39 for the pipe. I'll need the #42's someday anyway.


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## NeonGreenbangbang (Dec 20, 2008)

*Re: (slc92)*

Subroutines are codes or maps activated when certain predetermined conditions are matched by the ECM to enable some feature or function that is not considered through primary fueling or ignition. I'm not sure which VW ecm's have what subroutines or what routines they have and how they are activated, but things like Lean Burn or "Highway mode" are subroutines. Evap Purge is a subroutine. Knock Count is a subroutine for diagnostic of the ignition advance module and knock sensor. Knock count tends to be a dangerous one for a lot of cars.
By "Pop" I mean blow up.







Imagine that your ECM goes into Closed Loop, and parameter's are set for a Knock Diagnostic. It leans the mixture and advances timing considerably to look for a knock count. If it gets a knock, than the ECM knows both the knock sensor and ignition control module are working properly. Now, take the same situation, but we've been lying to our ECM. It goes to lean the mixture, but over leans it as a result of skewed MAF data. Typically not a "Death-To-Engine" scenario, but what if you are in slight (non-WOT) positive pressure and your last tank of gas wasn't the best gas on the planet? Well, you now have the perfect equation to create a brand new shiney hole in a piston.
Now that is of course partially hypothetical, and has nothing to do with C2's prom's directly. Lots of cars use C2's programming with great success and I'm not speaking poorly of Jeff or his code. This is purely exposition on what-if's. But things like that make me sleep uneasy at night because I have gone over data-logs where people can't figure out why they blew their motor and found that the conditions were just right for something like a knock diagnostic or highway mode to be activated. I'm not a big fan of lying to the ECM unless the lie is so complete that it becomes the new truth. In other words, if we are going to start misrepresenting airflow, every map that has anything to do with fueling or ignition should be gone over and altered to compensate for that. With between 100-200 MAPS in most ECM's, I very much do fear that there is a miscalculation someplace unless I am the one that did the prom. Why? Not because I'm perfect, but because IF the motor does go I have nobody to blame but myself. If I put in ABC Company's turbo prom and my motor does go up in smoke... how do I know what the cause is? No datalogs.... no knowledge of the prom data.... could be anything. I don't accept that kind of haphazard risk in my cars. It's imparitive that I know exactly what is going on inside the engine at all times. Hard to do if I'm not the one writting the prom.


_Modified by NeonGreenbangbang at 3:29 PM 12-22-2008_


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## CorradoMagic (Apr 11, 2008)

you should start writing chips for VW's. I like your way of thinking.


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## jettaglx91 (Jul 27, 2004)

*Re: (CorradoMagic)*

Neongreen-
i know you say your not stating your comments directly towards jeff and c2's software but as really the only and most reliable solution for the pre mk4 vr6, I'm not sure how to take your comments
I know your not saying you better but by questioning other peoples software makes it sound that way. 
Its easy to throw out a bunch of info to make it sound like you know what your taking about but please make your own software and i will gladly try it out and see who's is safer, more reliable, more powerful.
Im not trying to be condecending but as someone who has been here for years and has seen many things run its course, it just gets old when someone that knows computers or has experience with another manufacturer know more about vw's then the people who have already done it 
You gotta remember that jeff has 10+yrs experience with the vw and honda high horsepower application and a couple engineering degrees.
I dont know how it works but he must have done something right as there are hundreds if not thousands of cars running his stuff. 
For example my car ran fine on c2 software with a stock compression mk4 12v motor running 13psi for quite a while, 17psi a couple times at the track and still is running 100%
sorry for ranting


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## NeonGreenbangbang (Dec 20, 2008)

*Re: (jettaglx91)*








I started teaching people here how to burn their own prom's and was promptly banned because a board sponsor went into crisis mode.








Once again, it's nothing against Jeff. His software has supported more than one car here very well. I'm not advocating one company over another. I'm just more concerned with my engine management than the average guy I suppose because I have written so much code. Yes, written code, as in for ECM's that were so old they didn't use MAPs and didn't have software that could translate the data into a MAP structure. If you can't take that for what it is jettaglx91 I don't know what to tell you other than that you are very close minded. Jeff is not the only person on the planet that's been working with factory and non-factory management you are aware I hope. If you think his is the only way to run an engine, well, I hope it does great things for you. This isn't a pissing contest so don't try to make it into one for your own amusement. I don't need to sit here and qualify myself and I'm not going to take your bait to turn this into anything other than what it is. Experienced opinion. 
Here, have a gift. http://****************.com/smile/emgift.gif Merry Christmas.


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## slc92 (Feb 9, 2005)

*Re: (NeonGreenbangbang)*

What company runs a knock diagnostic under WOT? I work on Bosch systems all day and haven't heard of it. Perhaps they don't let us lowly technicians in on all the diagnostic functions of the ecu but I've never heard of this. 
Of all the "subroutines" on my vehicle I can't think of any that would cause the engine to pop especially since none of them that I know of are run at WOT. Vehicles are also tuned on the rich side to give you that margin of error. 
I appreciate your incite but I'm talking about modding a setup that happens to run a C2 chip. I accept the responsibility of modding my own car. I'm really not sure what you are talking about. 
You write proms, that's great. Write one that's plug and play on an OBD1 Corrado distributor that solves the stock MAF maxing out issue. Otherwise, the fact that you write proms doesn't really help me


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## NeonGreenbangbang (Dec 20, 2008)

*Re: (slc92)*

No ECM does a knock test in WOT. I never said that, you did....








I never said subroutines are run at WOT, you did ......








In fact .... I never said anything about WOT and MAF resolution issues.....








Re-read my post. You misunderstood a lot of it.
So my question is, WTF are you talking about? I was sharing information based on what I was reading. I didn't know I had to fix your car for you, but if you have money....





















http://****************.com/smile/emthup.gif 


_Modified by NeonGreenbangbang at 7:04 PM 12-22-2008_


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## jettaglx91 (Jul 27, 2004)

*Re: (NeonGreenbangbang)*

im not trying to start a pissing match in any way whatso ever, but the way you make it sound is someone else is doing it wrong (or at least not how you consider it right) but you know how to do it.
like slc said what is your solution on a corrado to run 42# or bigger injectors on the stock maf? if you can do it then how much would it cost?

i dont know jack about the inner workings of engine management but from what i gather is you dont think increasing housing diameter isnt the right way and talk about different scalings, but if the stock diameter housing will max out at x amout of flow how do you get around that?
im not trying to argumentive just trying to understand how can you get past a mechanically/electrical limit?


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## NeonGreenbangbang (Dec 20, 2008)

*Re: (jettaglx91)*

When I've had to do it in the past, I didn't have the luxury of increasing MAF housing size. I'm not completely sold on that being the perfect approach, you are right. I simply rescaled all the tables to accept half the resolution from the MAF, doubling my effective readable limit. However, there was a lot of headache involved in getting the car to run *Properly,* not just "Right." Either way, what I'm getting more and more here is that if people around here don't understand what a poster is talking about and they have a low post count, it's easier just to turn it into a challenging match against what they "Know" works, even if they don't know HOW it works. I guess it's just easier to plug in a prom that's not understood and bury the head in the sand, as is the nature of a throw away society.
It appears as if it's easier to make a new voice just go away than deal with something that upsets the comfort level. Fair enough... have your comfort, I'm available via PM if you want to seek me out. It's not worth my trouble to sit here and feel that I have to fight you guys off when it is you that has a problem that you can't solve..... not I.


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## jettaglx91 (Jul 27, 2004)

*Re: (NeonGreenbangbang)*

my question though is say a given setup maxes out the maf voltage (say 5volts) at lets say 10lbs. How is changing the software going to fix that if 5volts is all it can "machanically" read?


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## NeonGreenbangbang (Dec 20, 2008)

*Re: (jettaglx91)*

PM if you want.


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## CorradoMagic (Apr 11, 2008)

couldnt the voltage readings be calculated to provide increased fueling on less volatge? 
...inquiering minds(or at least mine) want to know
ie, MAF clamp w/ rescalled fueling?
simple example:
3v = 30# @ 60%
5v = 30# @ 85%
etc
take that and recalculate fueling via chip to provide adequate fuleing for proper A/F using larger injectors
like say..
3v = 42# @ 40%
5v= 42# @ 65%
etc
(just totally random numbers here for simple example)


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## the_q_jet (Mar 19, 2005)

*FV-QR*

awsome info here! Glad i understand most of it lol.


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## slc92 (Feb 9, 2005)

*Re: (NeonGreenbangbang)*


_Quote, originally posted by *NeonGreenbangbang* »_No ECM does a knock test in WOT. I never said that, you did....








I never said subroutines are run at WOT, you did ......








In fact .... I never said anything about WOT and MAF resolution issues.....








Re-read my post. You misunderstood a lot of it.
So my question is, WTF are you talking about? I was sharing information based on what I was reading. I didn't know I had to fix your car for you, but if you have money....





















http://****************.com/smile/emthup.gif 

_Modified by NeonGreenbangbang at 7:04 PM 12-22-2008_

No, you didn't say WOT. You said a subroutine could "pop" a motor. Ok so are you saying the motor is going to blow at idle? Out of boost? What subroutine on a VW is going to do this?
The issue is that the discussion is about fixes. You aren't posing any. Just poking holes in the ones that have been brought up. OK, we get it. The absolte safest, proper way is to rewrite the entire code. Awesome. I can't do it and no one offers it on my car past a 30# stock MAF tune. 
I'm not trying to argue w/ you and you obviously have some knowledge.
What's "ideal" is irrelevant if it's not available. Understand now?


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## farfimlosin (Feb 19, 2012)

adaptorman said:


> is it one of these types he needs


Where can i get one of these maf housings and i ripped one apart could i just plasit weld it into a pvc pipe or tig it to aluminum...it looks like that cheap white metal


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## cant get a password (Sep 24, 2004)

*Re: Why 4" MAF on 12v VR6*

I have one as well as a custom c2 42# dizzy chip I will sell cheap needed an afc to get it to run good but you can pick up a used apexi afc pretty cheap. I went standalone and no longer run a chip.

Sent from my SGH-T959 using Tapatalk 2


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