The upper hoses on most race cars including Nascar are -16, so it's plenty big. The heater hoses can both be -10 even though stock rubber sizes of course are 5/8 and 3/4.The conversion is fairly simple.
The -number is how many 16th of an inch.
So -4 is 4/16" or 1/4"
And dash -16 is 16/16" or 1"
I thought the upper hose was larger than 1" and the heater hoses aren't they 2 different sizes.