The brake booster hose was the 1st one I tapped into and the 1st thing I noticed, because I was on the brakes to leave home, was the brake peddle felt better. On the road brakes are noticeably improved. I was hesitant to use the brake hose because of concerns about braking performance but it actually went the other way and improved it.
as for which vacuum line to use on your IM... pick one, any one as it wont matter. As long as it is a direct connection to the IM and there are no check valves in between. Your comparison to using a capacitor is a good one
My recommendation is to use the 2" pipe that you have and tap it off the brake booster line. What I dont know is where the point of diminishing returns is. When I 1st started I had just the 15" piece that is aimed at the front of the truck, which made me think of the potato launcher joke. I had already experimented with the turning vane in the intake tube and knew the cause & effect so I pulled it, drove it for a few days to get re-acclimated to how it drove before that mod, then did the pipe mod. Being shocked at what it did, drove it for a tank and saw the mpg's jump similar to the turning vane (along with the bottom end torque jump). Once that was done I added the vane back into the intake tube and saw the torque shift back up the rpms some. No idea where that peak was. The next round I took the 9" section I'd cut off and added it to another un-used port off the IM. When I did that the torque came back down the rpms and it was pretty impressive at that point. Being greedy I pulled the air box snorkel off and the torque moved back up the rpms and it pulled way better in the mid range rpms.
So now I know that with more airflow thru the air box (same as the Ram - diesel), I can put that torque peak where I want it and move it with control over the flow into the air box. So like the ram, in comes the vacuum actuated exhaust cutout (boost controlled in the Rams case) to add that extra flow into the box on the fly. So under heavier loads & lower vacuum signals more air will come thru the box. My expectation is the mpg will suffer a tad bit at the expense of an overall improvement in driving experience. I'm OK with that as I've already gone from ~15-16 mpg on the commute up to the upper 18's-19's easily on mpg's.
So when I was done with all that (up to the air box mod, valve was defective, new one arrives tomorrow) I went after IM temps. They would spike into the 130's easily and impact performance. I took my favorite exhaust wrap and wrapped up the intake pipe. This helped to lower overall IM temps but it was still higher then I'd like. (they went from ~120-135 on the test drive down to ~105-120). I then looked at the engine and decided to insulate the 2 coolant lines you see wrapped under the intake tube. This further helped the IM temps from spiking and now I'm seeing peaks of 20~25* over ambient (mostly in the 70~90* range with some spikes up to 100~105*).
This truck weighs something like 4500#, has the worst gearing at 3.55's and the heaviest tires being an E rated 75 series profile. Performance wise all of the mods (70mm TB, larger intake tube and the vacuum mods) has taken a pretty boring truck to drive and made it significantly better and more fun to drive. The only downside in my case is the large evap leak code being thrown. I suspect it is monitored at the rise rate of the vacuum signal off the map sensor. I will eventually remove the pipes and verify that the CE light is tied to the pipe installation, then figure out a way to defeat the pipes at startup.
Please post up some feedback when you get it done, I'm curious to know how this works on a smaller IM. My assumption is your plenum is sized smaller overall which would make me think you wont need a large pipe to get the same results (torque shift move). Start small & work your way up so you see the cause & effect and can decide what works best for you.
Pic of my truck as it sits today, only addon is a retractable tonneau cover. I still need to add an air dam below the radiator support similar to what I did on the Ram.
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