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Discussion Starter · #1 ·
Making my own custom intake and it has all gone according to plan, i test fit it and it all fits in the small space you have to work with, surprisingly does fit over the battery and hood will close. With stock piping being 2.5" at the MAF sample tube, and throttle body being 2.75, i have a feeling this engine starves for air at WOT. It seems it was designed for common city driving (no long periods at cruise, infrequent WOT, low speeds, starts and stops), emphasizing as much low end torque as possible for good driveability, especially in automatic flavor.

As such, i went with 3" ID, 3.5" OD ABS pipe, ABS is desirable for an intake because it is light, will not hold heat, can be cut and "machined" or manipulated easily, and is also cheap to boot. With intakes the largest size pipe that fits within the confines of engine bay is the best, provided the transition to throttle diameter is smooth and relatively gradual, and bends are avoided as much as possible. Since plastic has poor radiant heat reflection characteristics i will be wrapping piping with reflective insulation when i finalize it. Getting the MAF to seal and secure to the pipe was easy, sensor dimension is about 1 3/8" x 3/8", i marked it out and used small drill bits to "machine" it out, the rubber seal on the flange of MAF will seal any small imperfections. Fastening was easy too, i slid the MAF into the pipe where it would sit, then drilled shallow holes using the MAF as a guide, making the pilot holes with a bit that is slightly smaller than the original MAF bolts. Then i just started the bolts into the plastic by hand and once they started making their own threads, used a ratchet to go right down into the plastic till they bottomed out, ABS is soft enough that the bolts are self tapping in a fashion and will create their own threads.

Now that's what i did. Now i need a cheap way of calibrating the MAF to match the increased diameter and lower sample velocity. It runs dangerously lean with this new intake due to this, enough that it will not idle. Still, i HAD to hear this thing, so i unplugged the MAF. The computer will then revert to predefined fuel tables that are known to be safe ( ie, really rich across the board). Sounds like a Subie at low RPM and high load! Loud as hell. It was addictive just driving around, so many people looked! Though i was running with no filter so it will probably quiet down once i get one.

Any ideas about calibrating an MAF WITHOUT any software? I want to get Osiris for this but i have to wait for that, my 87 Porsche 928 S4 project is taking priority right now. Anything to at least get the AFR at least roughly close to target, to make this driveable?
 

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Discussion Starter · #3 ·
Because i want to run 3" piping. I can make an intake better and cheaper than a $200 one. True performance never comes easy. Tanked up with 91 today, so it does idle without knocking now, but just barely. I'm wondering if i let it idle long enough, PCM will begin to adjust long term fuel trim from the consistently lean condition. Was also exploring a resistor for the IAT, PCM should advance and add more fuel. Just want to get it safely driveable until i can buy the Osiris tuning package. MR20 swap is in the future, and to squeeze as much as possible out of that i'll need to pony up for Osiris anyways.
 

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The only way to re-calibrate the MAF is the have the K-constant changed in the ECU, or run a piggy back. Since I dont think aftermarket tuning software exists for the versa, a piggy back is your only option. AEM FIC, Emanage, SAFC-II, etc...

The MAF is calibrated based on the diameter of the pipe the element is sitting in. Doesn't have to be the whole pipe, just the part where the element is placed.
However, making the intake piping bigger does not mean more power. having smooth non-turbulent air increases power. Also having a tuned length of pipe increases power by aligning with the pulses of air into the engine. Think of the intake like an instrument, it must be tuned to the right "note" for an increase in power.

edit: I should add you can support more power with a larger MAF. But a larger MAF will not add any power. If the stock MAF diameter is similar to most small displacement nissan engines, the MAF should support something between 220 - 250hp without maxing out the 5V range.
 

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Discussion Starter · #5 ·
Ok, so i would need tuning software to do this. That's what i was afraid of. I thought i could use some homebrew method of getting the MAF roughly back to stock calibration. I guess i will just use the stock MAF sample tube diameter which is about 2.5" i think. I know that the stock MAF diameter only needs to be the section where airflow is sampled, but then i might as well do the whole system with that same diameter, putting a reducer to 2.5" then back to 3" seems to defeat the purpose, and may even offer more restriction than stock with the added venturi and unecessary changes in diameter. The tube coming out of the airbox has a smooth bell mouth, so there is deffinitely merit in creating smooth transitions. That's why i also will be smoothing all the pipe section ends. I just wanted to try out 3" tubing to compare drivability and power band changes with stock, and see how it feels on the butt dyno. There is also a screen inside the intake i noticed. Whether this is to smooth airflow or is just there as a large debris screen i don't know, i was thinking of cutting it out next time i change plugs. I wish we had cams out there for the MR motors, then we could really fool around with airflow. Although there are companies out there that do weld and regrinds of stock cams, they do this for more rare parts like my Porsche 928 project car, not cheap but you can have them ground to any specs you want.

Trust me improving air path and reducing convoluted direction changes was a consideration when making this thing. Great thing about ABS pipe is that it's easy to work with and cheap enough that i can just keep making different ones, and the inside roughness is already smooth as a baby's bottom. All i had with the 3" experimental pipe was a 2.75" to 3.5" 45 degree elbow and the pipe running over the battery and terminating just before the front core support/chassis, much more direct and simpler. The silicone reducer/elbow was a nice smooth transition.
 

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Ok, so i would need tuning software to do this. That's what i was afraid of. I thought i could use some homebrew method of getting the MAF roughly back to stock calibration. I guess i will just use the stock MAF sample tube diameter which is about 2.5" i think. I know that the stock MAF diameter only needs to be the section where airflow is sampled, but then i might as well do the whole system with that same diameter, putting a reducer to 2.5" then back to 3" seems to defeat the purpose, and may even offer more restriction than stock with the added venturi and unecessary changes in diameter. The tube coming out of the airbox has a smooth bell mouth, so there is deffinitely merit in creating smooth transitions. That's why i also will be smoothing all the pipe section ends. I just wanted to try out 3" tubing to compare drivability and power band changes with stock, and see how it feels on the butt dyno. There is also a screen inside the intake i noticed. Whether this is to smooth airflow or is just there as a large debris screen i don't know, i was thinking of cutting it out next time i change plugs. I wish we had cams out there for the MR motors, then we could really fool around with airflow. Although there are companies out there that do weld and regrinds of stock cams, they do this for more rare parts like my Porsche 928 project car, not cheap but you can have them ground to any specs you want.

Trust me improving air path and reducing convoluted direction changes was a consideration when making this thing. Great thing about ABS pipe is that it's easy to work with and cheap enough that i can just keep making different ones, and the inside roughness is already smooth as a baby's bottom. All i had with the 3" experimental pipe was a 2.75" to 3.5" 45 degree elbow and the pipe running over the battery and terminating just before the front core support/chassis, much more direct and simpler. The silicone reducer/elbow was a nice smooth transition.
You're making this so much more complicated than it needs to be, you seem to have knowledge here but its a Versa making 122hp at the crank. Its not pumping out 600hp where you're going to gain a few hp going from 2.5 to 3 inch in the intake piping. If you wanna go custom keep it the same diameter so it doesnt mess with the maf readings and design it the way you want with less restrictive bends. Unfortunately there are no cams made for the mr18. I would like to see a mild street cam with more lift & duration that you can still use stock valve springs with. Give it that bumpy idle everybody loves
 

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Discussion Starter · #7 · (Edited)
Maybe i should just think about turboing it again, i have a GT 2056V turbo sitting around, just needs a new journal bearing. Getting the vanes to function as a wastegate and not melt would be a challenge but the piping seems like it would be doable, just cut up a stock manifold. Putting it over by the (former) battery area would cool down exhaust a bit. Hell i was even looking at how much room is in the rear muffler area. No temp issues back there.

As far as getting what i did to work, i just bought a cheap reducer today, stuck the MAF in the 2.5" (2 3/8" in actuality) portion, and sure enough it was fine. Might as well just do the whole thing with 2.5".
 
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