Horsepower capabilities? No other intank pump on the market can come close. This pump can support over 800hp using larger than stock fuel lines. This pump can still support significantly more power than a Walbro 255LPH pump even when using stock fuel lines.The Walbro 535LPH pump can flow anywhere from 15-120psi (the bypass valve is set higher than Walbro’s previous fuel pumps, which were around 85psi). Final fuel pressure is determined by your fuel pressure regulator. Please note that this is an aftermarket fuel pump, and some modifications may be required to get it to fit. The overal size is very similar to Walbro’s previous generation GSS340/GSS341/GSS342, however the base is slightly enlarged as shown in the pictures.