I recently installed this fan upgrade. I did not make any accurate measurement of the air flow rate but I did bench test three evaporator box/fan set ups for a seat of the pants test (actually it was an in your face test). I tested an original Behr evap box and stock fan, a Behr evap unit with the RetroAir fan upgrade and also an old '70s Kcool aftermarket evap box and fan. The Kcool clearly put out the most air on its high setting and probably more on the other two lower speeds as well. The Retro air was close to the Kcool fan and well ahead of the stock Behr fan. So if you are looking to upgrade or replace the stock Behr unit the RertroAir fan motor seems like a good step.
A side note on the Kcool unit.
Its fan motor is physically the same size as the RetroAir motor (so presumable has similar power) and also has internally variable speed which does away with the large resister bank that mounts in the air return from the cabin to the evap. These resistors are presumably mounted there for the air flow's cooling effect. So their removal (ala Retro Air's fan upgrade) will both improve return airflow and lower the evap return air temperature; both positive things. The squirrel cage fan of the Kcool is about 10% larger in diameter than the stock Behr unit. The outlet from the Kcool evap box is also about 20% larger in cross sectional area than the Behr outlet. I attribute these last two things to the edge that the Kcool blower has over even the Retro Air upgrade. I would have gladly used the Kcool evap box but could not find an modern evaporater core (actually I could not even find an old fashioned core) to fit it. So I had to compromise by going the middle road. I did try to fit the Kcool squirrel cage fan to the Behr evap box but it would take significant fabrication to make this work.
I am doing this retrofit to a 1973 911 as part of a full restoration. I will attach a photo of Retro Air fan upgrade installed into the Behr housing.
I hope this helps.
Scott
