In my experience with the vent motors the speed was close to the same so it could be your power supply is not putting out the 12v but...
with the new vent motor it's safe to use up to 24v and when you go up in volts the speed increases...maybe 1 to 3 rpm. Which is what you are looking for. If you have a 18VDC power supply try it.
As for your wiper motor make sure you are hooked up to low speed that might help because you wont need to reduce the speed as much. One other thing not all wiper motors are the same. I use to use maybe 20 a year in props and I found different models can work on different amps. So if you can find a 12 or 5 vdc volt power supply with 1, , or 3 amps (I've used a 1.5 amp to run a FCG one year with a wiper motor) it might slow it down...depending on the load on the motor.
But since you have the vent motor I would go with that. One other thing I just remembered...the new vent motor runs faster in one direction than it does the other. Maybe 1 or 2 rpms so reverse your wires from the power supply
with the new vent motor it's safe to use up to 24v and when you go up in volts the speed increases...maybe 1 to 3 rpm. Which is what you are looking for. If you have a 18VDC power supply try it.
As for your wiper motor make sure you are hooked up to low speed that might help because you wont need to reduce the speed as much. One other thing not all wiper motors are the same. I use to use maybe 20 a year in props and I found different models can work on different amps. So if you can find a 12 or 5 vdc volt power supply with 1, , or 3 amps (I've used a 1.5 amp to run a FCG one year with a wiper motor) it might slow it down...depending on the load on the motor.
But since you have the vent motor I would go with that. One other thing I just remembered...the new vent motor runs faster in one direction than it does the other. Maybe 1 or 2 rpms so reverse your wires from the power supply