Hello freaks, so I was reading the DIY intake thread, and on one of the last pages someone mentioned that the Hitachi MAF is the same MAF design as the Infinity G35 (late model) G37/ 370Z.

Upon further investigation I realized that the G37 intake kits on the market use a 2.75 ID pipe with a neck down to a 2.5 ID MAF flange.

I sat back and thought about it and I figured the Nissan GTR intakes would be worth looking into as well. As luck has it, the Nissan GTR intakes use a straight through 3 inch ID pipe with NO neck down, mind you these pipes have the correct MAF flange and the emissions nipple on the pipe for the PCV or what have you.

The kicker is that a ebay special kit or even a branded kit ranges from $100-400 dollars! Now you might be thinking "hey but Nissan G37/GTR's have dual intakes?" PERFECT now you can split the cost with a friend!

Yes it might take slight modification to the pipe work to make it fit in the GE8 but thats nothing a hacksaw cant work through.


My only question/ concern is users with the PRM or other GE8 intakes with enlarged MAF flanged pipes? Do you guys throw any CEL's from the MAF pipe sizing?

 

The PRM and other intakes that do not throw a code have stock size openings at the MAF sensor.

 

Good find! This is good to know though.

 

The MAF only measures air velocity and intake temperature. It has no idea of the cross section of the pipe it resides in. It is the ECU uses the velocity and temperature data with the known cross section of the pipe to calculate a mass flow rate. Using a 3" pipe when the ECU expects a different diameter, will not yield a correct mass flow rate. This is why every aftermarket intake will have the same MAF diameter as stock; to maintain compatibility with the stock ECU... Basically, The ECU will need to be tuned for the new MAF configuration.

However, if the stock ECU uses MAF data for all fueling including WOT, there may be a trick to get a larger MAF pipe diameter to work without a tune... For example, if you were to swap out the 185 cc/min fuel injectors for 270 cc/min injectors, which flow 46% more fuel, and increase MAF pipe cross sectional area also by 46% (diameter by 21%), then it should in theory achieve the same AFRs as stock. I have never tried this though, so I don't know for sure if this actually will work out this way, but there should be an optimal pipe diameter that can compensate for the higher flowing fuel injectors. If at any point the fueling goes to speed density, like my current FlashPro tuned ECU does for WOT, then there would probably be an issue unless you retune. I don't think this is the case though with the stock ECU.

 

I'm confused! So you say the Maf has no idea of the cross section (This means diameter right?) of the pipe it resides in. It only measures velocity and temperature.

The ECU takes this information in and adds fuel based on this info.

But then you say, 'Using a 3" pipe when the ECU expects a different diameter'. I thought the ECU doesn't know what the cross section is. It doesn't expect anything. It is only waiting for information from the maf sensor about air velocity and temperature so it knows how much fuel to add.

Which is it?

**Scratching Head**


Is all this to say that if somehow I put the stock maf flow sensor into a different diameter housing BUT simulate same velocities at similar rpms as the stock maf sensor in its stock piping, the ECU will be able to control air/fuel ratios just fine? It's not diameter based, just velocity based?


Just finished reading this --> How Maf Sensors Work

 

I said THE SENSOR doesn't know, meaning no actual calculation of the flow rate is done within THE SENSOR. It is the ECU that does the calculation, which requires the diameter to be known. Changing MAF diameter without the ECU being calibrated for the change, will cause an incorrect mass flow calculation.

 

Thank you!

 

well thats a bummer, the thread still holds true "GTR intake will fit with slight modification on a fit" but will the car run with improvement, maybe not. I read the civic maf tube diy and saw that you were seeing leaner afr, and yeah maybe slightly larger injectors would richen it back up to ideal AFR's. I will never try this though unless someone knows of $100 injectors to try. If I go that far though I feel I will sell the Fit and get a Si LOL.


I know what this car is meant to be but im trying to increase power ever so slightly just to have more commuting fun...

 

And you can! Just try to think 'outside of the box'. Make little changes here and there and if they are effective, great. If not, it'll be a learning experience that you can take with you for the rest of your life. A bunch of little changes that are effective can add up to a larger change (Ex: 5psi turbo) in the long run. And have fun doing it. Good luck!

The injector change is interesting. I'm now wondering what the stock ECU is capable of handling injector wise, if one is slightly richer than stock. That's something worth looking up. Thanks! BTW: I'm still looking into an Apexi SAFC Neo or other fuel adding part that can be done but those that I have talked too aren't capable of hooking it up to the 2015 Fit, without an ECU diagram.

 

This is correct, but in addition the changes from one size to another I.e, increase 40% is not as simple as increasing fuel 40% across the map. Essentially you need to remap the flow at all rpm/load ranges and retune with new data. Some people have done this using short term fuel trims and and whole but load of logging to get the data needed.
I'm running a sprinteX SC with restrictor removed and rdx injectors the Maf was maxing out at high rpm. I now know due to turbulence not size.

Stock Maf housing is about 2.5" on outside but funells down to 2" right at the sensor.
I have a custom 2.5" Maf housing I made with stock sensor and has really been a nightmare to tune with it.
Started tuning it with the SMT8l and it was a joke until I went with the AEM FIC6 but the only thing that allowed me to really tune it was installing a honeycomb like air straightener. After having logged 100+ hours I could clearly see the Maf is completely blinded by turbulence of my intake and the larger Maf tube making its data useless. Air straightener gives consistent readings and allowed me to tune it. In the end though I zeroed the Maf table and set it at about +40% tapering to 0 at higher rpm, like I said not to and tuned it from the fuel map using boost readings. This is more straight forward but harder to get idle and closed loop right.