or buy a set of rods and beat up ms3s all day. if you were going to waste time and money on any motor going into the msp other then a fs series it would have to be a mazda FE DOHC (or FE3 for short) Aside from a few crazy engineered bp installs, it is the only mazda 4 cylinder motor I know of capable of hitting 400HP on the stock motor. Best part is they used it in KIA cars so you can find parts easy. I found a genuine FE DOHC motor for $650, the KIA RWD version was like $700. There are differences between them obviosly but mostly the same randy stocker does a great write up on the motor and even made his into a 2.3l stroker using the 1st gen mx6/probe 2.2l crank and some custum pistons and rods he got for the cheap since they are the same as other common vehicles. id look inot that, 400HP on the cheap, just needs custom everything and a stand alone ems. I think he was looking for 230WHP non intercooled at like 6psi with the stroker motor, this is barely even working the motor so you can beat on it all day long.
