Hi guys,
There's been much discussion on the AC threads regarding various upgrades to condensers and their corresponding fans in an effort to improve cooling. I am working on a car whose early generations used the same Bosch fans as E9s, but on later cars they changed to British fans with lesser performance (as used on early some Jaguars). I am upgrading to the earlier Bosch fans as I feel they offer far better performance but wanted to quantify my decision.
Here's what I found the CFM and air speed of the bosch fans is. The fan blade diameter is 11". Taking into account that the effective 'blowing' surface are is .52 Sq. Ft. (does not include the center motor area) my air flow meter indicates a CFM rating of 1550-1600 CFm when wired to a running vehicle at around 14.2 volts. The steady-state current consumption is between 15.5 to 16 amps, close to 19-20 when starting for about a second. The airspeed is between 34-35 MPH.
Photos of the fan, CFM, speed and how far the sensing anemometer is from the face of the fan; same place the radiator would be.
I feel this is very good performance for its intended purpose. The 16" SPAL fans some have posted about have CFM ratings of around 1900 CFM or more but typically at much higher current consumptions. It seems those extra CFM come at a much higher current requirement. Of course, a larger fan will cool off a larger area of the condenser than this 11" fan. These Bosch fans have a highly pitched balde which contributes to its strong performance, which makes them far thicker than modern offerings that are required for modern ultra-cramped engine compartments, but not a deterrent in more spacious classics.
There's been much discussion on the AC threads regarding various upgrades to condensers and their corresponding fans in an effort to improve cooling. I am working on a car whose early generations used the same Bosch fans as E9s, but on later cars they changed to British fans with lesser performance (as used on early some Jaguars). I am upgrading to the earlier Bosch fans as I feel they offer far better performance but wanted to quantify my decision.
Here's what I found the CFM and air speed of the bosch fans is. The fan blade diameter is 11". Taking into account that the effective 'blowing' surface are is .52 Sq. Ft. (does not include the center motor area) my air flow meter indicates a CFM rating of 1550-1600 CFm when wired to a running vehicle at around 14.2 volts. The steady-state current consumption is between 15.5 to 16 amps, close to 19-20 when starting for about a second. The airspeed is between 34-35 MPH.
Photos of the fan, CFM, speed and how far the sensing anemometer is from the face of the fan; same place the radiator would be.
I feel this is very good performance for its intended purpose. The 16" SPAL fans some have posted about have CFM ratings of around 1900 CFM or more but typically at much higher current consumptions. It seems those extra CFM come at a much higher current requirement. Of course, a larger fan will cool off a larger area of the condenser than this 11" fan. These Bosch fans have a highly pitched balde which contributes to its strong performance, which makes them far thicker than modern offerings that are required for modern ultra-cramped engine compartments, but not a deterrent in more spacious classics.
