Quote:
Originally Posted by wstar
You're probably more aware than I am, but just in case: beware larger MAF tubes giving false MAF readings. The stock MAF sensors are calibrated for a given tube diameter, and they will read artificially low airflow numbers in a larger tube (which results in the engine running lean and not realizing it, because the MAF input is wrong).
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Well aware Wstar, but thanks. I've been building Bigger MAFs for Audi and VW turbos for 7-8 years now so I've learned some things along the way about matching fuel trims, Fuel pressure adjustments, Tube ID's etc. etc...
FYI here are a few MAF ID's
Stock 2.33"
Stillen 2.36" Estimate Based on typical wall thicknes of the 2.5" tube they use
Nismo 2.61" Estimate Based on ID of the 2.75" OD tube
I'm going to start out with these at 2.5" and see where it goes. I also have a venturi machined in at the inlet which tends to accelerate the flow a bit and bump the MAF output. The air will transition from a 3" filter flange to the venturi and 2.5" ID then expand a bit into a smooth 2.75 hose to the TB. This should enhance flow and volume.
A few tenths does make a difference in Surface area and MAF output. This car runs rich stock. My Scangauge reports a steady -8 to 9% rich correction (long term fuel trims in closed loop) unless driven hard and it'll drop to -4% for awhile. Typically when you nail the throttle and transition to open loop, these corrective factors get added to the pre-built open loop fuel map. The closer you can get to Zero, the closer you are to the Nissan spec'd preMapped fuel curves. There's enough headroom there to lean it out a bit and try to get the trims to 0%. These ECU's also seem to have a good adaptation range from what i've seen. I doubt the Nismo would go to that ID unless the car could adapt safely to it. Without having an adjustable Fuel pressure regulator, I'm just going to play with the air for now. Given that adjustability you could go bigger. Here's a little theory from my MoFo (Mass Oxygen Flow Optimizer!) page:
Modshack | Stage 2 MOFO (BAMM)