Anyone cut up a stock TPI MAF and put it in a bigger tube. Any pics? How did it work out for you with the re-cal of the tables?

 

i havn't but i wonder why do you want to do it ?? are you above 400HP ?? my stock MAF was able to handle over 420HP and it's limit wasn't reached

best regards

 

I came across a couple of TPI MAFs I had pulled when converting to SD. I am doing a turbo setup on a MAF TPI vehicle. Usually I just convert to SD, but was thinking of messing with one of these MAFs with the turbo. The stock MAF pipe would be maxed out. Targeting around 600HP........stock 350ci TPI with a cam.

 

When I bought my first TPI car something like 9 years ago, I insisted that that was the way to go and was told by a bunch of the ecm guys here that it will never work, that I'll never get the transfer function and resultant tables close enough, so I kind of gave up on it.

Since that I know that there was at least one person posting here on the boards (can't remember who or find them in a quick search) that mounted his maf guts in a 3.5 or 4" i thing steel tube and had it running well.

I cut the guts out of one and then machined a pocket in a 4th gen aluminum housing for someone, but never did hear how well it worked (actually, I know where the car is sitting under a tarp, hasn't moved since...)

 

My MegaMAF is 3.5" in diameter.

 

i tried to do it, but was way to much of a pain in the ***. I ended up gutting my stock maf along with the screens. My motor dynod put out 476 hp and 496 ft lbs torque at the engine. So it can supply enough air for at least my combo

 

What was the MAF reading for gm/sec? In other words, was it maxed out at 5 volts? This is what really matters in terms of it working without fudging it with the PE cal. hack.

 

What about using dual MAFs? Almost more of a visual thing under the hood. but would allow running a SD SLP-style dual intake, on a MAF car. The stock early 'bird intakes certainly restricted air flow some (like my 87 one).

 

Agreed. The ECM is the MAF's limitation, not the MAF itself....

 

No. You have been told a myth. The ECM is not the limitation.
That is like saying you can't use a 2_bar map with a 730/749 ECM because it was designed for a 1_bar map. There is just a loss in resolution.

The 0-5 volt signal of the map corresponding to 0-255 gm/sec is the limitation. If a large tube is used then the 0-5 volt signal becomes 0- 255+X. There is just a loss in resolution.
Yes, some cal. values need to be scaled for the bigger tube.

 

Exactly, the ECM doesn't have to know what the numbers mean, just how to apply them WRT to injector pulse widths and timing. Bigger MAF housing = lower output from the maf, just scale what that means to the rest.

 

No, I haven't. You are not going to reach 255/g sec at part throttle, with or w/out boost, and at WOT, there is simply no need for resolution w/out boost because the ECM switches to alpha-n. If the stock MAF's diameter was indeed a limitation then the whole point of rescaled chips extended to 0-512 g/sec used in conjunction with the stock MAF sensor would be absolutely meaningless. There are naturally aspirated cars running tens w/the stock TPI MAF sensor, and turbo buicks running low nine's w/their own stock MAF sensors, so the whole point in increasing MAF diameter would be defeating the purpose unless your planning to run much faster than that....

 

You are talking about something different. I am not worried about the restriction. Please list the code where it switches to alpha-N mode at WOT.
My goal here is to increase the range of the stock MAF. Yes, I could hack it using the PE mode like so many others have done. I don't want to do that. It is not a speed thing. It is a new project to play with and actually use the MAF input properly to control fuel for higher HP than stock applications.

 

How come nobody talks about how to tune the MAF tables for a 3.5" MegaMAF?

 

Never seen one. Is it a 3.5" pipe with stock TPI MAF electronics attached to it? Is it something you made or bought? If bought, please post a link.
Most people don't talk about it because for a long time MAF tuners considered adjusting the MAF tables as taboo. That is actually what should be tuned first. Then the values for setting error codes.

 

I made the 3.5" MegaMAF myself. Its fairly easy. You have to cut the stock plastic tube away (being very careful not to damage the sensing wire) and then silicone seal the electronics into an aluminum tube. You need to cut a rectangular hole in the side of the aluminum tube in order to insert the sensing wire of the MAF into the airstream inside the tube.

Then you have to correct the MAF scalar values for each MAF table, then calibrate each MAF table. I estimate my MegaMAF flows about 35% to 38% more air than the stock unit.

 

https://www.thirdgen.org/forums/tpi/...mance-maf.html

 

Did mine with 3.5" tube

Scaled the hell out of the MAF tables to get it to match my stock gutted screen MAF.



my 383 made 400whp at 6300rpm-6500rpm and i shifted at 6600-6800. It would hit max 255g/s easily by 4500-5000 rpm at WOT i believe it was, so i used PE enrichment vs rpm to get the fuel i needed. This was with the stock body MAF with no screens.

When i did the 3.5", i had to really upscale the MAF scalars to match the performance i had with the stock MAF. Thats all I did, kept my dyno tune and just changed the scalars until air fuel was about same as before. It worked well but the car didnt gain anything with the larger tube, but I also never redyno'd the car to dial in the tune, just used WB o2 to match WOT air/fuel mixtures.

 

Suppose the stock ID of the MAF is 2.8", then the area is 1.96
Going to a 3.5" pipe gives 3.0

That is an area increase of 3.0/1.96 = 1.56

1.56*255 gm/sec ~= 400 gm/sec max. flow (roughly)

Now all your scalar tables are off because the scale is 0-400 gm/sec, not 255 gm/sec. So if it was a stock engine you need to match up the new locations with the old locations. That would get you close and a starting point.
Example, suppose your 255 gm/sec value is 10 in the MAF table. That is the last location in the MAF table. That value of 10 needs to be moved to location 255/1.56 = 163. All the locations after 163 require a new table value for above 255 gm/sec.

Then tweaking needs to be done from there because your engine is not stock.


BTW, nice pics of the new MAFs.

Also, note that the LS1 MAF at 512 gm/sec follows the math above. 4" MAF gives 4/1.96 ~= 2, and 2*255 ~= 512 gm/sec

 

Orr89RocZ,
I bet if you looked at your tables and compared location values for the stock MAF and large MAF that they would line up at the scaled location value or pretty close to it.

 

I agree about not gaining any HP. I want to try the larger MAF for fueling reasons with a turbo setup. The thing is that it could go over 255 gm/sec at part throttle.......gotta love turbos. So, PE mode isn't of much use and doing the MAF mod. and ECM scale seems pretty easy.

 

On your area calculations you forgot to mult. by pi.

Does not really matter as your ratios are still the same. My 4" MAF meter actually seemed to flow 2.1 times as much air per volt. Rescaling the MAF flow tables is not the real issue. You do not really want to rescale the tables because you will still have the 255 g/s limitation and you will simply hit the 255 g/s limit at a much lower point in the table. You need to effectively change the fueling calulations according to the new MAF range (in my case x2.1 scaler). I also recommend changing the LV8 calculations and then modify your Tunerpro def file conversion formula where ever the MAF grams/sec value is used to display the correct g/s values.

 

Exactly, I don't do pi because it divides out.

Yes, there are many ways to do the scaling. I am not saying to rescale. I am saying to move values to the correct location.
Once again, there is no 255 gm/sec limitation. It is like saying you can't use a 2-bar sensor in place of a 1-bar sensor because the ECM doesn't read boost.
I don't understand why the MAF guys don't get this, but all the SD guys do.

Your 4" MAF flows as expected. You are hitting 255 gm/sec at the middle of the tables now which is exactly what I showed above with the 3.5" MAF. Your 255 gm/sec is at location 128. The 255 gm/sec with the 3.5" MAF is at 163 as shown earlier.

 

Here is a simple way to look at it. Go into your XDF file and change the gm/sec values of the MAF table to read from 0 to 512 gm/sec for a 4" MAF. Change to 0 to 400 gm/sec for a 3.5" MAF.

Now you will clearly see that your values in the table (BIN values) are in the wrong place. You need to move them to the right place.

 

No, you really want to leave them in the same place. You need to change the fuel calculations by the same factor to maintain the correct AFR relationship. The easiest way to do this is to go divide the injector value by the same factor (in my case 2.1). My MAF range is now 0 - 536 g/s (255*2.1=536). Then you also need to change the LV8 scalar by the same factor. The default LV8 scalar is 80 ( represents 80/64 = 1.25). In my case 80*2.1 = 168 ( represent 168/64 = 2.625).

 

I agree. As I said earlier there are a few ways to do the tables and the respective constants and LV8 values.

EDIT: I think the way you are doing it assume the engine is linear. Getting late & tired. I will think about your method be technically correct tomorrow. Good conversation though.

 

Looking at a stock MAF BIN here are some value from the MAF tables with a stock MAF

BIN gm/sec volts
182 59 2.47

255 254 5.0

I propose moving the value of 255 at 5.0 volts to the location of 2.47 volts when a 4" MAF is installed.

You propose doing a multiple at location 2.47 volts by 2.1. That is, 2.1*182 = 382 (overflow). Is this what you meant? I think that is why you are reducing LV8 so that the multiplies together come up with the correct value. That is, to limit the 8*8 multiple overflows in the fuel algo.

EDIT: I need to look at the code again. The AUJP (SD bin) needed some lines to be changed to correct something like this when large injectors are installed. Things overflow so the mults need to be modified.

EDIT AGAIN: I looked at the code. Now I see why you are doing the LV8 scale change. Yes, it is so overflow doesn't occur. Yes, the way you are doing it is the best way and looks to be the only way because of overflow problems.

 

I understand what your saying, but I was pointing out that the stock MAF's diameter really isn't a restriction. Most guys that I know simply don't want to bother with the stock MAF mainly because of the quality of the unit, but the limitation still resides in the ECM. The MAF provides a signal, that's all, it is still the ECM is which determines fueling in how it interprets that signal. From a TTA perspective, we know that the MAP sensor is not tied into the ECM, at all, and that it's only purpose is to drive the analog dash LED boost gauge, so by manipulating, or rescaling the translations from the MAF's signal in the code, the range can be extended to 768 g/sec if you really wanted to go to the extreme. In reference to WOT, unless the code is programmed to say otherwise, in naturally aspirated applications, PE mode switches to alpha-n; Target Air/Fuel Ratio vs. RPM & TPS, and MAF resolution inevitably becomes meaningless because the ECM bases fueling from the lookup table....

 

Continuing on with the example:

Looking at a stock MAF BIN here are some value from the MAF tables with a stock MAF

BIN gm/sec volts
182 59 2.47

255 254 5.0

For a stock bin with the MAF reading 5.0 volts:
5.0v -> 255 gm/sec -> 255 bin_value -> 255*1.25 fuel value

Using a 4" MAF with a 2.1 gain in flow, then at 255 gm/sec the input voltage should be 5.0 / 2.1 = 2.38 (round it to 2.47 volts).

The lookup will be at 2.47 volts in the table. Also, note the table values need to be divided by 2.1 and LV8 multiplied by 2.1

BIN gm/sec volts
(182/2.1) 59 2.47

2.47v -> 255 gm/sec -> 182/2.1 bin_value -> (182/2.1)*(1.25*2.1) = 182

Which is the wrong value. I agree that the table needs the 2.1 scale and the LV8 constant needs the 2.1 scale. This corrects the issue of the max value in the table being 255. This is the loss of resolution I have talked about. By gaining 2.1 of scale, then 2.1 of resolution is lost.

I also maintain that the table values must be moved. For the example, the value of 255/2.1 should have been moved to the place where the 182/2.1 is.

EDIT: Looking at the tables and how they are non-linear. It looks like the value of 255/2.1 at 5.0v should be moved to the value at 3.47 volts.

 

I looked at the code some more. It looks like the easiest way to do the larger MAF and keep all the constants correct without needing to rescale is to add another table. The reason being that all the other parts of the code that rely on the MAF reading. All would need to be modified. This means the code need to be looked over in fine detail to see where all the functions rely on the MAF signal. A lot are probably not in the XDF as is. It is also error prone for the end user to modify. I encountered the same problem when creating a boost $8D bin. It retains all stock functionality (EGR, PE, etc) and all that needs to be done is to fill in the new tables.

For a 4" MAF it does a mutiply by 2.1 to the incoming MAF signal so it looks like a stock MAF. The original code will work as normal without any changes. Then I use the actual 4" MAF signal to index into a new table that is for 255 gm/sec to 512 gm/sec. I set a bit in the code saying to use the upper tables and a new LV8 scale when the 4" MAF voltage exceeds 2.38 volts (or there abouts).
This way the end user leaves there original MAF table as is and just tunes the new table for 255 - 512 gm/sec. A new spark table is also needed.
In the boost $8D I just made a fuel multiplier & adder, and spark tables. Mods to the AE and PE modes were also necessary. I am guessing the same will be true here.

EDIT: I forgot the 16k bin is pretty full. Since it is small and there isn't a ton a places that LD / LV8 is used then it is probably easier to rescale instead of adding new tables.

 

junkcltr: no offense intended, but you are making this alot harder than it really is. My MAF tuning practice with the stock MAF descreened or my MegaMAF is to always put the correct fuel injector constant into the Eprom. Then go out onto the street and tune the MAF tables according to the BLM values. I adjust the gms/sec values in the six tables until the BLM are between 122 and 134. This might take several drives, but I have been able to successfully do this with my crappy Autoxray 240. In the case of my MegaMAF, since I thought that the MegaMAF would flow about 38% more air (simply the flow area is about 38% higher for my MeagMAF compared to the factory MAF flow area), first I addressed the MAF scalars so that I could increase the gms/sec values in each of the six MAF tables. Then I go out and drive around and correct the MAF tables. All of this can be done in one afternoon.

The WOT tuning should be done on a chassis dyno with a wide band o2 sensor. Here only the "PE VS RPM" table needs to be altered. You could use the "PE VS Temperature" table instead. Or both.

 

There are 2 problems with only doing the rescaling at the MAF tables (moving the values).

1. You still have the 255 g/s limit in the ecm. You have not changed the scaling of the 8 bit (0-255) airflow values used by the ecm.
2. Resolution is reduced by approx the square of the conversion factor (in this case the resolution will be reduced by approx a factor of 4). The 255g/s is now about 2.5v (by changing the meter) and you will be in saturation at less than half way through the MAF tables.

I tried this method and it works, but not well. Everything was much less stable, extremely difficult to tune especially at idle, and still could only make MAF based fuel calculations to the 255 g/s limit.

This is when I became convinced that the best method required changing the fueling calculation to rescale to the new g/s range (0-536). I found that because of the way the code is structured it is very difficult to change. I also looked at going to a 16 bit g/s value and found this nearly impossible due to the limited code and ram space. So... the simplest method I found was to change the injector value. Simply change the XDF conversion equation to multiple by the MAF conversion factor (x2.1) and then reset your injector value to the correct size. The other place the g/s value from the MAF tables is used is to calculate LV8. By changing the LV8 scaling factor everything based on load comes back into the correct relationship (have not run into any overflow issue at my x2.1 MAF conversion factor). Now the only thing left to do is correct the XDF definition conversions for any values that use air flow (g/s) such as the "Default airflow table" and the "Max Airflow vs RPM" tables to display the correct values. If you log through Tunerpro then change its definition file as well to display the corrected airflow values.

At this point it is pretty much standard MAF tuning.

Edit: I know conceptually this is difficult to grasp. I spent way to many sleepless nights thinking about this for many months, trying different methods, studying the code, researching here on tgo and other sights, etc. These are strictly my conclusions at this time and what has proven to be most successful for me. There are many ways to skin a cat, just trying to help get you there in less time than it took me.

 

Like I said above. You guys are making this alot harder than is really needs to be. From this last post, you do not hit the 255 gms/sec value until you are in the 5th MAF table. There are only six MAF tables, so whats so bad about that!. I know that some resolution is lost, but I will take the extra airflow anyday. Also, The idle RPM was the easiest thing to MAF tune.

 

Yes, in your case with a 3.5" MAF it is not as bad. However, with a 4" tube you hit 255 midway through the 3rd table. Idle was bad because of a ratty cam of coarse coupled with the poor resolution at low airflow caused for it to be not very driveable. Probably the 4" tube is overkill, but that is what we did and then the second part is strictly to beat the 255 g/s ecm limit.

 

Did this method implicate the car's overall driveability in any way....?

 

I agree. I think that the tables values need a divide by 2.1 and the scalar needs a multiply by 2.1. That makes the range happy in that the 6 tables have a range of 0-255 hex. The LV8 scalar does the mult. to increase the divide that was done.
That definitely needs to be done.
Beyond that I also think there is a need to move the values. I think you realize this too. You mentioned you hit 255 gm/sec in the third table. Suppose your engine was stock. The original MAF value at 255 gm/sec (6th table) is 254 and now with your 4" MAF reading 255 gm/sec at the third table. The value there is only 182 decimal. The 254 value should have been placed there. With the divide by 2.1 of course.

I understand exactly what you are saying. Your posts have been a big help. I will look at the calcs in the code some more. When I did the boost $8D I would make a speadsheet with the calcs including over/underflow. Once I got the eqns figured out in terms of range and resolution I would code it up and then test on the ECM bench. I will do the same here.
It is easy on the bench. I just put in a 0-5v signal on the MAF input and mess with it from there.

I was also thinking that low air flow may be difficult with the larger MAF due to turbulence / cam & intake pulses.

 

This has been talked about in the past. The code limit is 255 g/s from what I've read and like said above its complicated to change or there isnt much room to add stuff in a 16K bin.

I remember reading about scaling the MAF tables up while also cutting injector constants in half. In doing that, the net effect is like doubling the MAF limit or something like that. Its been awhile since I read posts about doing it so I dont know any more details. I never tried it since I never had a reason to with my setup...it just worked.

If I remember right tho, i scaled my MAF up alot and I think 255 was in my 3rd table Car ran good and even idled fine in doing this... I had a 230/245 on a 109 lsa cam to boot, and I ran open loop so everything was fine at idle. More work and I know i could have stabilized it more but i was happy with it. Car spent more time at WOT than idle anyway

 

I could just do it that way. This way helps me learn the code and get it theoretically correct like the original code is. Understanding the code makes it easier to tune in the long run. Have you looked at all your O2 lookup tables being wrong now? There are other tables too. Reading the code shows all this stuff that typically gets missed in just looking at the end results. All these little things add up so that the engine doesn't run just right.

 

The O2 tables would be messed up using the bigger MAF unless they were corrected for. Going to open loop hides that. I think a lot of people with bigger MAFs just mess with what is in the XDF and not all the tables & constants that need to be modified properly. We are only discussing the MAF fuel tables here, but there is so many more that need to be changed.

 

on a side note, i dont think i have my old large MAF bin file. It was on an old laptop of mine that died so I dont think i'll ever get that tune back to show what my scalars are with the large MAF. I have my 383 dyno tune with stock MAF however. I may look to see if i didnt copy that large MAF tune on my desktop computer.

 

I've estimated the flow of my MegaMAF to be about 908 CFM. This was determined by plotting other known flow VS cross sectional area. The flow thru the 3.5" MAF lines up very favorably with the flow thru my 52mm TB which has been flow rated at 899 CFM. So, at least I know that my MegaMAF is not a restriction. However, I am not saying that I go any faster with it, I just know that nobody can tell me its the MAF thats holding me back. And because of the above, I knew that it was unnecessary to go with a 4" tube which would definitely be over-kill.

Orr: Your MAF looks just like mine! And I am still jealous of your car.

 

Orr89RocZ,
Do you have a picture with a view from the outside of the pipe showing the MAF sensor? I am guessing that you didn't remove all the little screws from the plastic and make a mount. I have taken apart a junk MAF and all the wires from the sensor to the PCB are welded (not soldered). They would have to be cut and re-soldered to take the assembly apart. I am guessing you didn't go that deep into it, and just cut some of the alum. frame and plastic.

 

yeah i got a side pic. MAF is at my parents house in PA and i'm now living in TEXAS so i cant get any more pics.



I just cut off all the plastic and part of the metal frame to have just the sensor guts hanging out. I was careful with it and took my time but it worked out. I didnt have to take it apart or anything

Then i just cut the square hole in the pipe, and used QuikSteel epoxy putty to bond the sensor to the pipe. After it dried, i used Clear RTV to further seal everything to make sure no leaks. Worked good.

Complete 3.5" cold air package. Had to extend the wiring harness for this

 

Thanks Orr89RocZ. That is what I was picturing but wanted to make sure. I don't think it is worth disassembling and possibly breaking a pin/wire. I think I will do the same with the MAF I have.

I wanted to use aluminum pipe, but all I have is 3" and 4". I do have some 3.5" steel so I think I will use that.

Now I just need to get crackin and study the MAF hac. It has been about 5 years or better since I have looked at it.

I ran some quick numbers (115 cfm/sq in.), (10.86 hp/lb/min):
MAF diameter / theoretical CFM / theoretical HP
2.8 / 707 / 540
3.5 / 1100 / 845

The CFM doesn't jive with the ECM calling the max. at 5 volts 255 gm/sec.
255 / .567 = 450 CFM

 

Is the MAF going to be able to handle the air demand with a turbo'd setup tho?

Most air to air intercoolers have 3" or so exits so it has to jump up to match the big tube MAF. I just hope you can measure the air volume since the internals of the MAF in a 3.5 or 4" tube will not be centered so alot of the air is going past that without being measured. Under boost its just gonna get worse

 

After looking at post #9 in this thread: https://www.thirdgen.org/forums/tpi/...mance-maf.html

And seeing the great info. that the university did I went and looked back at the MAF tables. At 4.71 volts the 255 gm/sec is met and saturated there after. So, it does jive with the 520 CFM that was measured on the flow bench.


Orr89RocZ,
Yes, I was wondering that too. The IC inlet outlet change isn't a problem. At worst, I could buy some 3.5" alum. and weld that on there. I will have to put the MAF in the most straight section to minimize turbulence and unequal flow. The other thing is low flow fluctuations at idle.
Overall, I am not sure how it will all work out, but if the flow is constant then it should be fine. I really don't know though. I plan on doing the 3.5" because the 4.0" is way over kill for what I need.

 

4th gen guys have seen some gains with the larger MAF's. They make 100mm MAF's now for them which is incredibly large. They finallly have a MAF thats larger than their 90-92mm TB's...and they even make one larger than that I believe.

But those guys are up near 600whp on n/a large inch setups. Lots of them however go with a speed density only tune

So 3.5" is plenty large.

 

there are 2 reasons why your ratios aren't working out exactly. One you've hit on is that now you've got the sensor offset to one side of the opening so any turbulence or even laminar flow differences across the maf opening will change your numbers. Fords always have this problem and if you look at their stock and most aftermarket setups you'll see that the maf tends to be mounted on the outlet of the airbox (chamber of slow moving air) to a longer length of straight tubing (straight airflow). Even then, but especially when you mess with it/add a blower... you can significantly change how the car runs by changing the orientation of the sensor/electronics by spinning it around a few degrees.

secondly, if you look at a stock maf housing most are not straight tubes, but venturis (tapered through the middle), which to some extent gets rid of the turbulence/uneven flow problem by forcing it all towards the middle.

 

From posts #47 and #48: Yes us 4th gen guys have 100mm MAFs, I am running one on my 402 LS stroker in my '99 Camaro SS. This 100mm MAF is the largest one we have at this time. 100mm is 3.94".

One thing that we have not done right is that we should be squeezing the 3.5" tube into an oval shape. This will put the metering section in the middle of the airstream and an oval shape will match the oval shape of our TBs.

 

And also lose area which means less flow. At 4" it doesn't really matter.