Stock boost is set around 5.5 to 6.5 psi. Once you hit around 7.0 you will hit fuel cut so you will need to pick up a fuel cut defender first. You can pick up nearly 1 psi with just a cone filter and a 2 1/2 Inch custom turbo back exhaust. But just by doing this it will give you fuel cut. The filter, exhaust, FCD are three of the best mods for the FC3S and you will notice a quicker spool, you will be able to here the turbo spool, and a noticeable a good increase in power. It is not uncommon for guys to pick up 20 to 25 at the ground with no tuning from just these three mods. Most of this is due to the restrictive air box and the two or three cats and the small size of the exhaust piping. I do not recommend going passed 7PSI with out a front mount and some type of fuel management on the s4s it could be bad(no). A word of caution if you run any type of cone filter it must mate up to the MAF apexi makes a good filter and adaptation plat you can pick up for around 80 bucks. You may want to start posting in the RX-7 section. But fill free to PM if you have any questions. Welcome to the forum.
