hondo - please read the ABA post linked to twice above.
In your original posting you claimed an instant improvment but that was ont he same route in different directions. What you want to do is to create a test with the minimum of variability except for the mod you are trying to test.
But as you asked how about something like this :
1. Select a route, maybe a circular route round a city or town on a highway, some route you can use cruise on consistently. Make a note of things like temp, wind direction, weather etc. Photos are good too.
EDIT - route should be a decent length - 50-10 miles at least, car should be warmed up etc.
EDIT2 - All runs should be in the same direction.
2. On your route select a start and end point - e.g. a bridge.
3. Top off your tank and do a number of runs on cruise unmodified - reset your MPG gauge at the start point and note the average at the end point. See how consistent they are - if they aren't then maybe change the route as they should be very similar. How many runs you do is up to you - one probably isn't enough, 10 is maybe too many.
4. Fit the mod.
5. Repeat 3 (including topping off you tank) with the mod fitted. Again the results should be consistent with each other with the mod in place.
6, Remove the mod.
7. Repeat 3 - full tank again. Again the results should be consistent with each other without the mod and should be similar to the results in 3.
For best results all of this should be done in one go - so you have the same weather, temp, wind etc. but that can be tricky and even inside a day the weather can change but we don't all have testing labs. Topping off your tank each time ensures the weight of the car is similar.
For bonus points take photos or video the test - a mobile phone is good for this but for safety use a mount when the car is moving - decent ones are $15 or less on Amazon. The more evidence you have the better the test.
Look forward to the results.
