Stock MAF Housing VS Big Bore MAF Housing (76.2mm ~ 3") Technical Discussion
 

During last weeks dyno, I wanted to see what the difference was between the stock 72mm MAF housing and my 76.2 big bore MAF housing. No tuning was done between runs and the same MAF sensor was used during both runs. The blue line is the 72mm housing and the green line is the 76.2mm housing.

http://hsvracing.com/upload/6spd_Hay...%20Housing.jpg

Comments?

First of all, thank you for doing this back-to-back comparo. I <3 these kinds of threads.


Anyway, I wonder if the added HP/TQ is attributable to the added airflow capacity, or to the advanced ignition timing. :scratch: I would tend to go with the latter simply because there is a significant gain even at lower RPM. But it also seems like the big MAF housing changed the shape of the curve up top. That might simply be a variation in cam timing though. I wonder how they'd compare with identical ignition timing curves and how much the different VTC maps affected the results.

Edit: The a/f was off-the-charts rich up top during the stock MAF housing run. :eek:

nismology, you are correct, the a/f was very rich with the stock housing.

Here is a chart of the comparison of the gm/s of the two housings...

http://hsvracing.com/upload/6spd_Hay...BMAF%20gms.jpg

I looked at the Intake Cam Timing for all of the runs comparing the stock MAF housing to the BBMAF housing. Doesn't look as if they were affected at all.

http://hsvracing.com/upload/6spd_Hay...m%20Timing.jpg

Interesting. Do you think it'd be possible to normalize the scale to 100% of their respective maximum values though? On an absolute scale it's kind of hard to compare them head-to-head. :slant:

Nismology,

I did not grab the data during the dyno of the timing (for some stupid reason) but I do have some timing comparison data back when I originally installed and tested the new BBMAF.

http://hsvracing.com/upload/6spd_Hay...ing%20BTDC.jpg

For those of you who would like to see the runfiles, they can be found at the link below:

http://hsvracing.com/upload/6spd_Hay...Dyno/Runfiles/

For those who know Excel, all data, charts, and analysis can be found at the link below:

http://hsvracing.com/upload/6spd_Hay...-26%20Dyno.xls

:surprised

So if the ignition and cam timing are relative unchanged for the most part I think it's safe to say that the physical size difference on its own is enough to provide some gains. Exactly how much HP remains to be see seeing as though the only other variable, AFR, was different between the two runs.

Teaser...
http://hsvracing.com/upload/6spd_Hay...g/100_0607.JPG
http://hsvracing.com/upload/6spd_Hay...g/100_0609.JPG

Btw, great work Hayes! :thumbsup: I'll have to hit you up online sometime.

When you correct the A/F the ignition timing would go back to the original cell, but the top end gains are still impressive. It's pretty much from air flow alone. I saw this a few years ago when I did back to back tests on Jon610s car (2k3 Max). After the SSIM, 77mm MAF and SAFC tuning, he walked out the door with +22whp. Each item I installed made more power, and then more again after tuning. The MAF gains alone were impressive, complementing the SSIM.

IBmadefromrecycledmountaindewcans

no screen on yours? i guess it doesnt matter, in your case the a/f was leaned out. i thought when the screen was removed the air had a tendency to not be in a uniform flow (not equal through the cross sectional area) and the maf would read incorrectly? using the same maf sensor i assume? maybe more gains to be made with a screen, maybe lost, i dont know.

I don't want to rain on anyones parade here, as this thing really will add power, but it appears everyone needs to be reminded that you should NOT just install a larger MAF without the ability to correct the fuel curve (SAFC2, VAFC2, EB, EU, etc.).

:sprint:

No matter how many times I've linked dozens of members, and repeatedly stated YOU NEED to have some AFR control(via AFC) and AFR monitoring is HIGHLY recommended as well, some STILL insist on just 'adding' this.

My car ran like buttocks when I used a larger ID MAF housing w/o AFC. Even more lean than the OP's. I blame it on my TS tune. (AFR was gone/off the charts of my wbO2, 19.9+).

while i agree with you about the safc need, youre 82mm maf is a 37% increase in cross sectional area over the stock size, while the 76.2 is more on the lines of a 15% increase. thats a big difference especially for air flow. i think it would be reasonably safe to run the without an a/f controller, but we all know that with a controller you will get more power nd it will be safer

General discussion and questions about the MAF housing and its potential sale have been moved here: http://forums.maxima.org/showthread.php?t=528750 If you want to continue to discuss it in general, please post in that thread. Posts not technical in nature will be moved there as well.


Not censoring anyone. I just want to keep this thread clear for technical discussion so please keep your posts in here as such. Thanks. :)

SR what is your take on running w/o the MAF screen on a bigger MAF? Is it really unnecessary? I have done some searching and found nothing real concrete. Judging by this thread it seems to be ok, would running w/o a screen put more pressure on the sensor reducing it's life or its effectiveness?

Search MAF screen + SR20DEN on here and you'll see his take on it:ben:

do you guys think that this will have the same increase on a 3L? i got a buddy who's going to make one for me and we'll try it out on back to back runs when the car is ready for a dyno. i'm just looking for a little input on if you guys think it'll be worth it on my car. thanks

There is only one way to find out. :idea: I would think it would provide similar gains, but as I stated earlier, only one way.............

because of the increase in bore, I'm assuming the computer leans out the AFR because the air flowing in is at a lower speed? correct me if I'm wrong here...

Is there a way to increase the speed of the flow or mechanically adjust the AFR without the use of the AFC? I mean, I know that's the BEST way, but could there be a Velocity stack added? I'm just posing some questions out there because I'm very interested in this, and I know FI isn't exactly in the stars for the 3.5L...at least mine >_>

I've had computer-designed exhaust systems for little 100cc motors that would create a suction effect and produce more power than a straight pipe or open exhaust port alone could hope to achieve. I've always been curious about generating this effect on the intake side with out resorting to FI.

... You're correct, read the threads on this, the data is there to support this.

Airflow? Any reason why would want to do this?

On an A33B, :grinno: Have fun converting that fuel system

Tell me how you know. :Popcorn:
Not to be a hoot....but instead of tossing ?'s, do some research, the data and information is there.

Wrong forum.

damn, eat my post alive. I'm just trying to produce some educated conversation :gotme:

I already said no FI for me, so I'd be here, in the correct forum :P

Being that modern engines are hugely affected by computers and their input, I didn't think it would be any easier to do a mechanical adjustment to AFR rather than jacking in a piggyback module and have it tell the ECU what it needs to fix.

The engine size shouldn't matter when utilizing a design theory from a smaller engine, should it? In fact, the more displacement should increase the effectiveness of such a design.

And why wouldn't I want to increase the velocity of the airflow across the MAF and into the intake? the sensor could richen the mix back up into a more optimal range and the bottom line for doing this mod; more air into the engine, why wouldn't I want to increase the speed at which air enters the TB?

The fact that a larger MAF housing makes more power proves that volume > velocity, IMO. :gotme:

#1- What you were refering to originally about the exhaust system stuff and it increasing velocity to create a suction effect for more power... thats scaveging effect. Works great on the ehxaust side of the motor, not so useful on the intake side. The intake side you want to draw in as much air as possible, period. Thats what will yield the most gains in power (this thread as proof).

#2- Physics, thats why. Just because it moves faster through the MAF (faster velocity), doesnt mean its flowing more air into the motor (Volume). Scavenging Effect rules hardly apply to the intake, thats where you're getting it all mixed up. To make it flow faster, you'd use a smaller diameter tube for the MAF, which will do the exact oposite of the gains proven in this thread. It'll act as a restrictor and decrease the flow more and more as the RPMs go up.

EDIT- Dude, look at how rich he was with the stock one, why would he want to go even richer "to a more optimal range"? He was already off the scale rich!


Bottom line- Just because it works on exhaust, doesnt mean it will work the same on the intake side. On an NA car, exhuast side is being pushed (scavenging effect applies), intake side is all suction (doesnt apply), so the more air (volume) that the motor can suck into the CCs, the more power it will make, be it through means of bigger MAF to match the tubing's ID, port and polishing the intake manifolds, agressive cams, etc...

But our TB's are still 70mm :Popcorn:

This is where velocity starts to become more relevant (bahaha)! inside the IM>heads> CC. But infront of the TB, blah to that :wall:

TB are 75mm stock!

Question would a 80mm be overkill. I can get one of a M5

Not from the rear. The front part of the unit flares out a bit.

Thanks for the info 95BLKMAX. I guess I'm just trying to see if there are additional intake design elements that could be implemented to effectively increase power and efficiency.

Maybe I am looking at the graphs wrong, but under the stock MAF, it seems like the AFR is only in the optimal range from 2500-3700rpms then starts getting crazy rich, while the BBMAF seems to be quite lean up until 5100rpms where it drops into a more nominal range. If I've been doing my research right, it seems that a common AFR range that produces the best power in the VQ is around 12.7-13.4. If creating a faster flow AND the increased volume of the larger MAF could be effected, then in theory, the greatest volumetric efficiency could be achieved.

...and maybe I have no idea :gotme: :hide:

Higher flow = less timing, so we think. That's why I wanted you to go back for a little more reading on the subject.

From the sitckys ---> http://forums.maxima.org/showthread.php?t=434821

According to the input from the OP on these BBMAFs, Timing appeared to be unaffected vs stock. So :gotme:

You're correct, but the way timing is increased in the link I provided is a little different in that it's a drastic change in MAF V (obviously not as much as 72 - 76.2mm) So maybe I don't know :wtf: I'm talking about. :reading: Maybe I should do some timing logs comparing my MAF's :bonk:

If you increased charge velocity by not changing anything else, then that means the VE is higher.

Well, after digesting that entire thread you linked to, and re-reviewing the charts on this, It seems like briefly the Timing advances from 2-6deg on WOT from 2800-4000rpm, then tapers off back in line with stock timing. Maybe there is some airflow or exhaust threshold that is reached and the ECU starts readjusting the AFR. when i was racing 2-cycles, the engine builder actually told us to tune AFR through exhaust temps. I know, according to the list, the O2 was simmed, but what about the 3 other sensors? are they all simulated in this instance? my guess would be the primary O2 on the headers may be giving additional information to the ECU that's telling it to start correcting the fuel mixture. I honestly can't find any direct correlation to the timing advance vs Airflow in those ranges. The last I heard; the rule on the standard ECU is that the system would run static settings until a condition of both 40%T and 3000rpms is reached. In the case of these dyno runs I'm going to assume that it was WOT so it should start correcting AFR IMMEDIATELY at 3k rpms. In this case the AFR graphs and raw data don't support the ECU doing this, at least in the case of the BBMAF, until maybe around 4000rpms? Perhaps the O2 sim is having an effect on the AFR correction factor the ECU is pushing? Maybe the 02-03 ECU has a different Threshold at which to run open loop? :gotme:

--It's always 'adjusting' according to MAF/CPS input when WOT.

AFR using a wbo2 is more accurate than EGT's. EGT's can get higher/lower and it's not always hotter = leaner.

O2's do not have any input re: AFR when WOT.

-- That's what the FSM states, but there have been members that have proven that it is not always true. Seems to be only under very light load where the ECU is in closed loop. i.e. not always 3k/40% TP.



Not what the FSM states. Any WOT condition and the MAF seems to take over. In my experience, only under very light load seems to be when the O2's are in charge. MAF seems to be in charge @ idle and WOT regardless of what the FSM states.

well, I guess that explains the reasoning behind so many people discussing this information here. I would imagine since the conditions in the FSM don't always apply it would make it much more difficult to establish a base tune that would at least put most people within good range than with this wild AFR and timing variances. It seems to tell me that if I go after this or even the M62 MAF that I'm going to need to get a baseline dyno run; apply the new MAF body, and camp out at the tuning shop for a week to get it dialed in. I never thought to ask, but is there any injector swap or AFPR implimented in the Op's case that may have an outside effect on the AFR?

PS- Thanks for the info on the WOT vs threshold on the open loop conditions. The linked article + the FSM would have led me to believe otherwise if it haden't been observed by people here. :support:

Settings for EB, SAFC2, etc.

1. Q45 MAF in Z33/A33 MAF out.
2. Moderate A/F tune
3. ????
4. Profit

If it takes you more than an hour to do that, you're doing it wrong.

I'm a perfectionist, a nit-picker, and I'm probably exaggerating substantially in my case. Would that mean I'm doing it wrong if I apply the stuff that takes me an hour then spend the next couple of days making little tweaks? :nervous:

Little tweaks @ what? You can do everything SR mentioned in an hour, AND get at least 4 runs in (part of #2 on his list).