Well done with that adjustable throttle cable project.
I would stay with matching inlet pipe sizing to the MAF and TB. There isn't much to gain with making the pipe bigger than the MAF and TB, maybe for all out racing. There are many other things worth doing before that. The 70mm TB fits the intake opening well enough that no porting is really needed. Fitting the 75mm is not a huge change, it wouldn't take much to match that better.
It's worth making the TB larger than the intake manifold, but not a bunch larger, and the gains drop as you do. But it does help, and the key to getting the most out of it is the PCM tuning, it needs programming to richen the mixture.
Any airflow increase will increase power, at all rpm's, given the proper A/F ratio and timing. The A/F and timing are entirely controlled by the PCM, and it is not perfect. The PCM does not make perfect adjustments for all changes. It does very well for anything except big changes, like the MAF, injectors, boost, or boring/stroking. But for all the little things, there are gains with new programming, thus wait to do the PCM after the big stuff. Live with the random results of the minor changes, some will improve power at all speeds, some will not(result of leaner mixture).
I will not debate bigger versus smaller. I know that I'm correct in my power theory's, and I know that the smaller is better is wrong 99% of the time.
I also know that bigger up until some random magic figure you make up as an individual, that is wrong also.
Bigger is always better for most I/H/E parts except a very few. The headers are very critical, they need to be big enough to support maximum power in the upper rpm where the vehicle is run, and no larger. The collectors also need to be sized for the primaries to gain the most from scavenging. Those parts just like camshafts should not be selected by non professionals. Always get a pro to select those for you.
Consider the parts you are looking at, what will they cost given a smaller cheaper version, versus the bigger higher end stuff. Pick the parts that are in your budget, don't plan to buy multiple parts. Do not buy two sets of heads, exhaust sizes, TB's, MAF's etc. If your goal is acceleration, go for the biggest that you can afford, and start with budgeting the PCM programming. Programming is not dirt cheap, but compared with buying more than one of any part, it is inexpensive.
91 Lincoln LSC/SE/GTC, 99/93 Explorer Limited 4WD,
98 AWD Mounty, 98 Limited with 255/55/18's, big sway bars, and 12.75" x 1.25" rotors.
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