double helix
bighammer is right
The 215 pump has a double helix design cam that allows it to pump a lot more fuel, the 160,175,and 180 pumps do not have this cam design and cannot pump the amount of fuel of the 215. An example of how much difference is when you slide the plate on a 160,175,180 pump you get about 15 –20 hp when you slide the plate on a 215 pump you get about 50 hp. Besides the cam the plungers are larger (can’t think of the size right off the top of my head) and the delivery valves are 181’s instead of 131’s (there may be other stock sizes but not sure).