I have always found that if the rear is running hotter than the front, you can open the cowl flaps an inch or so to get it in line. This seem to slow my plane down from an average of 150 to 148. This is then a 1.33% decrease in speed x 150 kts x $4.00@ gallon fuel = a net cost of aprox. $1.06 extra in fuel per hour flown.
The rear louver kit installed seems to be $3000-.
Therein it would appear that you would have to fly your plane aprox 3000 hours before you would receive the first dollar in benifit from the mod.
But they do look cool
