My vote is on worse MPG... Yes the TPS and the butterfly will be more open, but in intake restricts more air. I beleive a similar effect would be seen with a dirty air filter, which according to the 1st thing to do to your car is a bad thing (tip top running shape). I have also seen posts of people replacing the factory air boxes with different types of intakes that restrict the air less and gain mpg.
Remember the engine is basically an air pump, the harder it is to get air into it, the less efficent it is. I could be completely wrong, but that is my thinking on it.
If the swap did end up in better mpg, I would assume having a restrictor plate would be more efficent since the air would have more area to move in the larger tubes.
Either way you go with this, keep us informed
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