There is also a placebo effect of the CAIs when they are tuned. By itself the CAI makes the truck run a little bit lean. A lean engine has a higher power output than a rich running engine. When you get a custom tune you are not compounding the power because your truck is getting the same performance tuning AND getting recalibrated for the intake. If you made 1/4 mile runs before and after I can almost guarantee the times would be very close.
And the throttle body spacer is only going to act like an intake manifold extension (and a comparatively puny one at that). You also risk having a leak at the spacer that could cause vacuum issues. Read the EPA reports on them. Even the Environmental Protection Agency says they are a dud. Spend money on the pulleys before you try the spacer.
I have heard that you can swap intake manifolds with some of the mustang 4.6s. Theirs are designed for more top end power because mustangs dont pull trailers regularly. I would even look into that before getting the spacer. If it will work find a junkyard 'stang and pull it off of that. Will probably be cheaper.
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