found it.
http://www.enginer.us/
so, it's roughly $2000 upgrade, plus 4 hrs pro install, or eight hrs DIY with an option of messing up HSD. I'll round it up to $2500 with pro install at $120/hr labor.
right now, mine does about 38 mpg, and climbing, as warmth finally came back( she did 42.5 last summer). gallon of gas is $3.8 here. that's 10 cents a mile. mine does about 560 miles before refills. if i do 1000 miles on tank, that's roughly 450 miles difference, or x 10 cents, $45. $2500 : $45 = 56 tankfuls. at current rate, i fill up twice a month. with doubled mileage, it will take one refill per month. or, 56 : 12 = roughly 5 years of driving to offset the cost of that gizmo.
considering that winter time mileage goes significantly down, i'd safely extend that period of time to 6 years. i will most likely not own that car in 6 years. i drive about 20 000 miles a year, x 6 years, will put her into current 60 000 miles, plus hypothetical 120 000 miles to offset the cost, total 180 000 miles. no, don't think so..
of course, gas may be 5 bucks next year. but then again, hybrid wars already started, after Germans and Koreans stepped into that market. I'd say, it will be more feasible to buy a new, more mileage efficient hybrid vehicle in about 2 years, than to upgrade what i have now. ( I have my ways of buying cars that makes it more efficient)
terribly sorry. all my calculations are wrong. i glanced at their front page, where it said: starting from $1995. in reality, for Prius,
starting price is $3495 for 4KWH Kit
and that's for Prius!! which is a much smaller car. no, no, forget it. too expensive and takes toomuch time to offset cost.