Stock Maf Limits
 

I figured I would post this up in a new thread instead of burying it in my build thread as it will probably be useful to a bunch of you. Running the 2.5" boost tubes the stock MAF will max out right around 10.5 PSI. Anything higher than this is quickly starting to exceed the capabilities of the stock MAF. Which at about that boost the car puts down ~530hp. I am currently trying to take the stock block further just to see what it can hold.

Hope this helps someone going boosted and trying to figure out their air needs.

Very informative was debating between 2.5" or 3" on the intake tubes...

The Fast Intentions Intake tubes are indeed 2.5".

They have run them past 650, and within safe limits. From what I have heard, they can take up to 750hp(theoretically) on their particular kit, no doubt 700 is within sight. I daily drive north of 610 on 12.6psi. On a 2.5" intake tube.

Your mileage may vary, maybe it is based on the kit setup, but they have found the stock maf easily capable of 650 without a reason for concern!

That's aggressive as hell, even on E85. I like your style! :excited:

You sure they dont flare up to 3" at the MAF? Not sure how you could anymore air though this 2.5" it just wont happen. I would be curious to hear any feedback directly form specialty Z.

For me right at 10.5PSI my MAF voltage is around 4.60Volts getting very close to the 5 threshold and IMO at the limits of the sensor.

Maybe altitude is playing a role here. All I know is I am most defiantly maxing out my maf running over 11PSI.

Mitch...the tubes in which the MAF's are housed are 2.75" with the BP turbo kit.

I think F.I had 2.5" tubes to begin with, and found that they max out too early. They had switched over to 2.75" tubes a while back.

My mistake Sasha. Im curious as to how the FI kit can run over 10.5PSI and not max out their MAF.

Thanks for the clarification I thought they were 2.5s.

What is your MAF voltage at 10.5psi?

~4.6-4.7 at 10.5PSI

Unless your kit is just moving that much air on the top when compared to the 2 smaller turbos?

Usually tuners push the sensor voltages deep in to the 4.9V's, and can get the additional couple of psi.

It'll be interesting to see where the voltage will be once I make those 3" charge pipes for you.

My MAF curve is your typical exponential one and when I log what uprev is reading for its conversion to flow rate it pegs at a constant number after 10.5ish telling me that the sensor stops differentiating between an increased airflow. Ill play with it more this week.

Thanks Sasha.

This could very well be the case. Either way, what I have in there suits me well until about 700hp.

I personally don't really care whats in it. If its functional, reliable and powerful, it can be 1" or 6" haha! That's why I pay Tony and Seb to do it for me! :tup: Either way, it's cool to hear some fun plans in the works for both BP and F.I. kit owners. My 2.5-2.75" tubes won't be around much longer...unless someone finds a way for them to support much much more than 700hp.:tup:

Stay boostin' my friends!

I daily drive north of 610 on 12.6psi. On a 2.5" intake tube. NWO THATS A SICK statement ( In a good way) LOL GODANM!!

Well I hope the BP tubes can handle 14-15 lbs cuz thats what Ill be running in the next couple of weeks.

Dare I mention that we are also using puny gt28rs turbos, 2.5" exhaust, and a stock block?

BUT yes, daily driving a 600+hp/550+ftlb 370z is an absolute BLAST:happydance:

Back on track, my tubes are DEFINITELY NOT 3" at the maf, measured them today, outside diameter is quite a bit short of 3"...if that helps any! I dare not pull anything apart, I have no leaks, no concerns, again I will leave that to Tony/Seb unless it's a dire need type of stuation.

Well then I guess I have to revisit what i'm doing with the MAFs. Maybe Ill try cleaning mine and see how that goes.

Can anyone check the voltage that they are seeing? Ill do some more testing on my end and post up a log.

I did some logging today and here are both runs. You can watch the MAF go all the way up to 5 Volts. I guess with Sasha's kit its just moving that much air at 12-13PSI? There is nothing in the tune that would lower the MAF voltage.

http://img.photobucket.com/albums/v2...ps7b6ccf51.jpg

http://img.photobucket.com/albums/v2...ps988ec4d4.jpg

You can see it maxes out at 4500rpm (which is crazy low). I pulled both MAFs and they had some oil on them but I cleaned them and reinstalled them. I have no idea how you guys are running higher boost on a stock maf with 2.75" boost tubes.

MAF Settings for reference

http://img.photobucket.com/albums/v2...psf46b2745.jpg

http://img.photobucket.com/albums/v2...ps89f7d50d.jpg

Now you have me worried I wont hit my goals with the stock mafs. Is anyone running 14+ with the bp kit?

Unless my MAFs are different than other stock MAFs I dont see how anyone could run more air through these 2.75" boost tubes with them in their stock location.

BBRSpeedworks put me onto these which takes advantage of the laminar flow in the boost tube and the fact that the friction along the sides of the tube actually slow down the incoming air and thus allow you to read higher flow values with the stock MAF by moving it out closer to the edge of the boost tube.

Hitachi Slot Style MAF Mass Air Flow Adapter Flange, FORD and GM- TREADSTONE PERFORMANCE

Nice! Simple cost effective solution, if it works. Did you order these up Mitco?

I think I might try them just to see if they work, I think ultimately I will just end up running 3" boost tubes though as that seems like a more permanent solution.


Edit... On second thought they are not just spacers but it looks like the maf adaptors will have to be torn off the current boost tubes and these installed. Too much hassle for me, I thought they were just spacers at first.

U could get them cut of and grinder down then weld on the new ones..

For reference, with my Greddy kit that uses 2.75" MAF tubes, my MAF voltages are ALMOST maxed out in the 9psi area. I hit 4.9's in voltage. But boost pressure is not exactly an indication of airflow.

While I agree with you where the MAF is being measured the restriction to airflow past the maf should be consistent engine to engine unless you have extensive throttle body or plenum mods. Or if you figured out how to increase flow via VVEL. This is measuring the boost right after the MAF on Sasha's kit. But your right, where you measure boost can have a very large effect on what your seeing vs how much your flowing when compared to the next guy.

What is interesting to me is how it is not common knowledge that these stock MAFs are not suitable for what I would call over 475-500hp on stock sized MAF tubes. It can get very dangerous very quick when you get into the upper ranges of the MAF.

Airflow and pressure are not directly relative anywhere you take reading or measure. Different turbo systems on the same engine will achieve different airflow mass at the same pressures. Which is why I have my MAF voltage nearly maxed out and I am not even at 10psi boost.

Care to elaborate?

If you have the same restriction downstream of a flow and it is in steady state conditions you will have a very similar flow as long as the device reading the flow has the same cross sectional area. Albeit if you are not in a steady state condition when dealing with air you will have density changes as the pressure changes as it approaches a particular restriction. If pressure was not relative to flow you couldn't have MAP tuning on engines at all as you would never know the mass of air being ingested by the engine.

While I agree with what you are saying I reason that if you have some constant variables then the system becomes measurable and if you wanted to even tunable based on pressures instead of flow rates.

I see you did a ninja edit there.

I agree with you up until you measure after all the modifications. If your measuring at the turbo outlet then yes, you will have restrictions that cause pressure and reduce flow. But if you measure right at the TBs then it doesnt matter what is pushing the air before it, all that matters is that air is getting to the engine at some flow rate. This is assuming your IATs are very similar to another platform you are measuring against.

Its like having a large industrial fan pushing air through a very long cylinderical pipe, while at the same time using a small fan through a short pipe. If you cut both pipes such that you want the outlet flow to be the same it no longer matters what was before the pipes. All the losses incurred through the system happen before the point of measurement, not after it.


Again I could be wrong, but its how what I was taught sat with me. I will have to go find my fluids text.

The discrepancy I believe you are missing is that a MAF sensor is not "boost-smart". Once you are using the MAF sensor in a blow-through application, while you will maintain repeat-ability in the installed application (hence still allowing for a consistent and safe tune), there is no longer any direct correlation between MAF voltage and PPM of air. You are now tuning based on literally just MAF voltage VS RPM, rather than a known quantity of air vs RPM. Without outside data collection such as boost gauges and logging, while tuning the UpRev, we would be entirely blind as to have any idea how much air mass is entering the engine.

I agree with that 100%. I would suspect with higher pressures your going to have more air available to cool the sensor and "fool" it under pressure. That explains how on a NA car you can still see ~4.6 volts yet it still works under boost which much larger flow rates.

Exactly. Tuning with a blow-through MAF configuration is sort of a middle-ground between MAP tuning and MAF tuning. With a pull-through MAF configuration, we would get the results we want to expect of a MAF sensor, but unfortunately we would top-out the MAF sensors extremely early. With our blow-through MAFs, our ECU will detect additional airflow, it just will not detect it accurately. But its not exactly that important, since we are recalibrating the maps based on the end results... sort of a "manual closed feedback" during tuning.

One interesting flaw in pull-through MAF configuration in boosted applications is the lack of an additional air temp sensor in the plenum. The compressor and intercooler will have such dramatic effects on air temps that having the only air temp measure taken after the air filter is not dependable at all. I wonder if R35 GT-R has an additional air temp sensor... I dont remember seeing one. I will have to try and look that up.

Charles, there is air temperature measurement circuits in each of our MAFs. To the best of my knowledge that is required to work along side of the airflow to determine its rates.

For example an uncalibrated MAF with no temperature sensor would read a very different airflow at -20 than at 80 degrees since all were doing is measuring the rate at which the flowing air cools a resistor in the MAF circuit.

I am very aware of the air temp sensor in the MAF! You are correct, it is required for the MAF to properly function.

What I am talking about is how the MAF sensor in a pull-through configuration such as the R35 GT-R will not be aware of changes in air temp caused by the compressor and intercoolers. Therefore the ECU will not make air temp corrections (for fuel injection) based on air in the correct location.

To accurately apply air temp corrections for the fuel tables would require a secondary air temp sensor in or around the plenum, after the intercooler and compressors.

Sorry I misunderstood you...

Id have to see the tables in the computer to see how it runs. But if I am going to take a guess I am going to say that they utilize the MAF for idle and low boost conditions, then switch to a speed density type calculation when the MAP reaches some threshold.

Also regardless the MAF measures a flow rate, all the system has to know is that amount of air is in the system and will be ingested. It doesnt matter if it heats up or cools down from there as all that would do is slow down or speed up the incoming air, which works fine on a recirc type setup. With an open dump setup this would all fall apart as now your going to have metered air leaving the intake tract. However on a recirc setup I think your error would be minimal and under WOT id expect the system to use the MAP anyways.

Ah ya youre right, "brain-fart", changing the temperature of the air after the MAF doesnt change its volume it just changes its density.

The change in temperature is going to cause both a change in volume and density the MASS will remain the same as read by the MAF, unless the pressure changes in which case density and volume could remain unchanged with the increase in pressure.

Mitco, while a plenum IAT sensor isn't very important as far as calculating fuel demand and air mass goes if you have the one in the MAF, timing and temp corrections for burn speed and injection angle are going to be effected greatly if there is an unmetered increase in air charge temperature.

ya ya ya, catch me on semantics. MASS is exactly what I was talking about.

there ya go. good point back to my original thought, i wasnt even considering the side effects at this depth yet.

While I agree with you on basis I would argue that real world adjustments to the fact would cause very little if at all 0 changes to the overall output of the engine since we are not dealing with direct injection engines. That argument would be valid if we were talking about emission generation and controlling the hydrocarbons. But usually when one is concerned about that it is during a constant state operation such as idling or cruising down the interstate.

On a direct injected engine that does not rely on the fuel evaporating (and thus cooling the charge before it hits the engine) I would say that yes it becomes a greater concern, in fact all the diesels I tune have a IAT right before the air hits the plenum for that exact reason. The IATs have a large effect on the burn rates in direct injected engines because you do not have the cooling evaporation effect before the air enters the combustion chamber.

Again its just my opinion on the matter. Plus if you look at the Uprev timing tables there is only so much fine adjustment available to the end tuner. Its a limitation to the memory in the ECU.