on my 2008 Apex MTX i dropped a tunnel dump exhaust, and boss seat, shredded about 40 lbs and gained about 5 hp. some guys also toss in a fuel controller for more tweaking, all 3 will run you around $3500.00 with installation.... not a boost but some good mods for that heavy ass Apex lol I no longer have my Apex, I switched back to Cats
Another good mod is going with a K&N filter and carb kit, pipes, and you can never go wrong making it lighter. Then you can go with Nitrous for a big bump in power.:d
On my nytro I ran a Hauck Header, K&N intake, MBRP silencer and different plugs. Worked really good for me also changed the track and cut down the tunnel. This summer I found a good deal on a turbo but HP is a addicting so once you have a little you always want more.