DIY Throttle Body Spacer

[Jakins]

have you noted any MPG gains?

[Tesla]

Just found this study on plenum volume and efficiency.
http://muhserv.atauni.edu.tr/makine/..._files/A/e.pdf

Although they talk in terms of increased volume, the experimental design describes the use of throttle body spacing, they found overall improvements from 1,700-2,600 rpm at the expense of reduced performance beyond 2,600.
I'm guesstimating they used around 1" & 2" spacers on the bases of a 2 1/2" diameter intake duct, bigger than 2 inch reduced overall performance.