hi guys I am rebuilding the motor out of my 98 Eclipse GS 420 I had a few questions about My build. I am using Crower stage 3s, I had my head rebuilt with new seals in guides and 5angle valve grind, then ported and polished along with the intake. my question is what else do I need to finish this build? my short block is factory and freshly rebuilt as well. well I need a tune? well I need aem cam gears? how much power can I expect to gain from this set up? should I have my head milled to make more compression? thank you for any help or information guys greatly appreciate it!

Don't mill the head because if it needs rebuilt ever you will be buying another head if it's out of tolerance. Should of went with oversized valves. Use stock cam gears for what you're doing. With a stock bottom end you might gain around 20-25hp with what you have depending how good your head flows maybe a little more. With the stock injectors you can just use the stock ecu unless you have big plans down the road get megasquirt. An underdrive pulley would help too. Egr delete, bore the throttle body or get a 60mm tb, header exhaust ect.

On a stock bottom end and a stock ecu you will more than likely lose power with that big of a cam.

Deff need a bigger TB, and a nice intake manifold to get some use from that big of a cam. You should of considered getting a high comp piston with the block rebuild. IMO you should of gotten a stage 2, does not seem like you are ready for a stage 3

You def want something along the lines of an afx ecu if you can find a legit one. Another option is a Syked reflashed ecu. The stock ecu is going to kill any power you could have made. The best option would be MS. You should also get some adjustable cam gears with the 3's too.