Digging up a somewhat old thread, but I just thought I'd give my 2 cents, which might be wrong, most likely in fact! LOL
Anyway, for our uses in the "eco" world, I would think that modding/changing the intake in front of the throttle body would be pointless.
The reason I say this is because the things that matter and/or make the difference are the intake runners on the other side of the throttle body (the intake manifold) which some of them these days physically change length via rpm. Beyond that, other designs use variable valve timing that again, change via rpm. Both of these designs are for maximizing breathing and top-end power for the "performance guys", yet on the other end also maximizes breathing, power, low-end torque and efficiency on the bottom-end for us "eco guys".
So short of running either of these engine designs at WOT, there's really no point in modding/changing the intake before the throttle body.
At this point, I'm not saying anything about cold air or hot air as I haven't read up on that yet. I've just seen it mentioned here and there on this forum as well as on GasSavers.
Exhaust systems on the other hand should help both performance and efficiency. For improved top-end performance you would most likely go with larger than stock pipes, a 4-1 header, larger free flowing cat, muffler and delete the resonator altogether. For efficiency on the low-end, you would probably go with a Tri-Y long tube header (4-2-1), same size or possibly smaller than stock pipe and free flowing cat, resonator and muffler. Both systems should utilize mandrel bends for near constant flow speed.
Again, I am no expert on any of this. This is all just information I have picked up over the years from all types of sources. To me, it seems to make sense, but like I said, I could be and possibly am wrong.
