I have no idea dude!! That's one of the nice things about being a mod. Everyone ASSUMES you know everything. I'm still pretty new to this gas stuff, but I'm a very quick study
. Personally, I don't like the look of the HPI pipe, and I hear it's not as well protected as it looks. The rear plastic on the baja flexes a lot on bad landings, I've seen quite a few pics of that pipe bent and sheared at the manifold.
Consider in my 20 years in RC, consists of 2 years of electric, 17 years (with a 5 year break in the middle) of nitro and nearly a year of gas now. I'm a relative newb...