automationgame.com

Ok. So I design an engine. I see the horsepower, etc. Where do I see the mph specs on the engine designer or the fuel economy (miles per gallon).

Not sure what you mean MPH? The engine can't have a speed, its just an engine in a stand.

MPG you can't tell until the engine is in a car as you'd need to know how heavy the car was, what gearbox it had, how much drag the body had etc to calculate that. All you can tell from an engine is how much fuel it takes to make each horsepower

Put it this way, MPH is a factor of transmission gear ratio, final drive ratio, maximum engine rpm, and tire size.
For example, you are building a performance rear drive vehicle with a tire size of 315/25R20 on the rear, a sixth gear ratio of 0.85:1, a final drive of 4.225, and a redline of 8000RPM. The top speed for this vehicle is 173.7 MPH, or 279.543 kM/h.
If you would like to do more calculations of this sort, use the website below. I can easily spend hours on it.
http://www.zealautowerks.com/transcalc.php

OK that makes sense of course.