My last 2 tanks were around 25 and 28 MPG, but with wind and rain, and some hill climbing and deadlocked city traffic on the 25 tank. The tank before I installed this was 28, with warmer temps and clear weather, with only a little wind and rain. I'm pretty sure the kamm is having a positive effect if I can match a good weather tank in poor weather.
However, I'm not sure how the overhang is affecting things, and whether or not it's altering airflow along the sides. Other kamms I've seen have the top and sides end together. I'm considering shortening the top to meet the sides, which would take 9 inches off of the length and I'd lose 2 vertical inches. Cutting it off would give me slightly more use of my rear window and allow my trunk to lift higher.
I'm thinking of making it more like this:
http://ecomodder.com/forum/showthrea...html#post63182
Thoughts?