The three home-made-units that I tested last year (during Spring/Summer/Fall) were long and wide, similar to the one in the picture. I do not have an actual temperature for your reference, but I did drive my car around and then raise the hood to find the carb cool to touch while it was idling. Keep in mind that my Challenger dual snorkle hood has the two vents open so the outside air is coming into the hood while driving (50 deg minimum outside temp) which could have had some affect on the temp of the carb. But I was surprised to find such a temperature difference between the carb and the motor though. Even after a while of driving, the carb was warm but definately not close to being hot. Then after the engine had been shut off and it started to heat soak, my fuel bowls (glass sights) only raised about 1/8". This was enough proof for me to try and have a permanent shield in place by this coming Spring.

Note: I just checked Summit and the three that they show are not as wide or as wide/long as the one that Cool Carb is showing. I found that when the shield is stretched beyond the front/rear of the bowls is when they seemed worked the best. This makes the hot air from the intake go out and then up around the carb when rising instead if going straight up under the bowls.

I attached a picture showing my second revision. It may be a little hard to see because it is clear.