No, there are NO engine restrictions for late model dirt cars in the US. The ONLY restrictions are one carb and one spark plug per cylinder.

But, we raced primarily on short 1/4 and 1/3 mile tracks and sometimes we had RPMs down as low as 2500 under race conditions. So, engine response was important. And the 800CFM was seriously worked---flowed well over 900 CFM and the fuel curve was good for our type of race car.