Carb Heat Delta T

I have been working on my carb heat system. The original system was just for show. With the new system I have 100% sealing of the cold ram air, so the heated air is not diluted at all. Heat is coming through a Robbins Wings carb heat muff installed on the cross-over such that the air is drawn from close to the oil sump. I installed a carb temp probe to track my results. Here is the first flight:

Lycoming O-360-A1A with Sam James cowl:

OTA - 41 F
Carb temp at idle - 64F (the result of the oil sump)
Flying 2,400 rpm - 43F
Carb heat 2,400 rpm - 68F
Carb heat 2,200 rpm - 74F

I have the Robbins single pipe carb heat muff and ran it to the Vans valve but have the leaks sealed up at the Vans valve so all air comes in through the muff. The temp rise is about the same. Keep in mind, that ice only forms with the inlet in a fairly narrow temp range. If the air is to cold, the air isn't carrying the water vapor necessary to create ice in the throat. So, say if the air is at 25F a 10 degree rise will get you to 35F and no ice. If the air is colder than that it doesn't carry enough water vapor to create ice in the carb. With the inlet air at temps above freezing and the throat at or below freezing are the most critical.