Even the stock magnum can make 400 hp with ease. The only ones to avoid would be the chinese made replacement heads, they are lousy quality. They are the real cheap ones on e-bay and do not have 318 cast onto the runners. You need to call and ask the company if they are the EQ because some of them show a pic of the EQ but are actually selling the chinese version, the company that does that is the one who told me about the chinese junk. I am not trying to make this political, the chinese are humans and deserve to be able to make and sell stuff, just this particular product is junk.