[bondvagabond]

Thank you aero head for all the great input. My e-350 is actually a 1993, I think the one in your link is a 2012. Ford did a body change in 92 or 93 and redesigned for less drag. Supposedly my factory c of d is 0.37 not great but better than some of the stuff coming out today.

My van is also the factory long version, 20" longer behind rear wheels. I know from my time as a boat builder that the same design stretched was always more efficient for displacement hulls anyway, that do not plane.

I've been agonizing over doing a turbo or a tuned exhaust designed to be most efficient at intended rpm zone of 1400-1600rpms.

The only data I could find on that was for the 1.6 vw diesel. Both the na and turbo use the same compression ratio 23:1 and using the EPA specs the na diesel is 9% greater efficiency. All the other diesels I have found the factory drops the compression ratio for the turbo motors. This comparison is more like what I was contemplating of adding a turbo to the already higher 21.5:1 compression ratio of my na motor.

Both my 7.3 and the vw 1.6's are all mechanical idi's so without being an engineer I think This data dictates that I stay na and build a custom tuned set of headers and exhaust