So I see that most of the intakes long or short tube have a section of reduced diameter where the air flow meter sits (along with a mounting boss for same).

I understand that you want to keep the area around the AFM the same as stock so you get an accurate reading... but, with that as a pinch point, what is the benefit of the bigger tubing elsewhere? Can't flow better than the most restricted part of the system. At the most, bigger tubing before, but same size after or you're having flow losses from the drop of velocity after the pinch.

Reason being, I'm not seeing why I can't get an $80 kit for the tubes with the AFM bosses and then piece together a long tube system. I probably have the filters in a parts bin along with silicone connectors. I just can't justify almost $500 for 6' of aluminum tubing and silicone. But I'm not an engineer, and don't want to miss something vital in the intake path.

My experience was with RX-7s, and when we went from top-mount to front-mount intercoolers. We'd use aluminum mandrel bends with a bead roller and silicone with t-bolt clamps to put together the airflow from turbo outlet to manifold inlet, and kept everything the same diameter. BUT, that is a vane or cone type AFM, not the hotwire like the VQ uses.

 

Increasing the diameter at the air flow meter requires not only a larger diameter unit but also reprogramming the ECU for the different voltage values generated by the new unit. Nothing difficult, just expensive since you have to buy two meters.

 

My question was rather, why enlarge the tubing *after* the calibrated AFM section? Any benefit?


The commonly available short-ram pipes I see go something like 3" down to 2.25 for the AFM then back up to 3 to the throttle body. My question is why go back up to 3"? Wouldn't the air flow faster (and therefore cylinder fill faster) if it just stayed at 2.25?

 

I was told there is some power to be gained if you will go bigger after MAF.
I have "re engineered" my r2c short arms to CAI. My tubing is 2.5 and goes to 2.75 if i remember correctly...

 

I'm going to guess that the MAF and TB are off-the-shelf for Nissan so economies of scale trump power output. I don't think the MAF needs higher velocity than the TB but who knows?

 

You're gains will be minimal at best and not the dollar to hp gain ratio