For those that choose ease of maintenance along with performance gains, the single 40/44 HPMX is the set-up of choice. For the basic 1600-1800cc, the 40 HPMX Kit is a torquey option. For all out performance, the way to go is the 44 HPMX. The 44 HPMX carbs in these kits have 30mm venturis and .55 accelerator pump jets installed.