That's one of the weird things about these engines. You can actually increase the power and fuel economy at the same time. Doesn't seem to make sense but what's happening is the engine efficiency is improving. The HD valve springs are a good idea. If an exhaust brake is in the plan they are a must. Kits often come with both the 3000 and 4000 RPM springs but it would be rare you should need 4000. Best fuel economy is in the 1700-2000 RPM range. You just need a bit above the stock 2500 RPM to help with gear shifts. Stock injectors and turbo should have no problem getting to 200 HP or a bit more. Like I mentioned, it's a good idea to have the injectors checked. When their pop pressure is closely matched the engine runs much better. Check the turbo for unusual play. Rebuild kits are not very expensive should it be needed. Your stock turbo is the HX30W with a 40mm inducer. Those turbos also come in 42, 44, and 46mm versions, If down the road a bit more performance was desired, the 44mm is identical in appearance to your stock model and would be an easy swap. The 46mm version is called the Super and some plumbing changes would be necessary, but nothing major. Don't know how much you plan to dig into the engine you have. It is often good to pull the oil pan and inspect the bottom end bearings, Replacements are not expensive. New rod bolts are supposed to be used when you do that. Since you are looking at efficiency, you could have the bearings coated by Polydyn in Texas. If you were going to tear it completely down, they also do special coatings for pistons, Just all kinds of small mods that can be done. Head studs are another good mod. One that could gain some more efficiency is having the turbine housing and exhaust manifold ceramic coated to keep the heat in. That isn't a very low budget mod. If you haven't already, need to install a pyro gauge sensor. Pyro and boost are two mandatory gauges.
