less rpm, my car top speed now is about 150km/h.

if i will start engine rebuild, i want to do it once, that mean i will change what ever needed or not needed :) to be sure..:))
what limit HP for this eninge build? i mean can i make it ready for 400hp ? if i will use NOS in future ?
or 300HP is maximum?

You will also need a Boundary Engineering billet steel oil pump for 300whp. The factory oil pumps sometimes fail at higher horsepower numbers (above about 250) because the gears are weak and the resonant vibrations are strong. The factory harmonic balancer is known to sometimes fail from a combination of age and strong power. When you go above 250whp, you should maybe look at replacing the stock one. There are two good options for them. This one, and this one.

Around 300whp will be the limit for the stock intake manifold, that turbo (GT2560), that iron exhaust manifold, maybe the intercooler, the turbo downpipe, maybe your clutch. You will need a 3 inch diameter exhaust from the turbo outlet all the way out of the back of the car and low restriction muffler.

The injectors are good for only 300whp. The 5 speed transmission is only good for about 300whp.

If you are looking to lower your engine RPMs, changing from your 4.30 rear gear to a 3.90 gear out of a 1.8 car will help that a lot. See this gearing calculator.

it so interesting to see such good advice's from you, thanks a lot, your posts are very clearly.
ok that mean i will build engine as for 300HP, what about NOS will it be possible for rebuild ed engine?

I'm happy to help.

NOS is a possibility, but you will be limited by the turbo's hot side (turbine) and the rest of the exhaust (manifold, downpipe, exhaust pipe, muffler) because it will limit flow capability for the gasses trying to get out of the engine. Adding NOS is like adding much more air into the engine. It still needs to get out of the engine. When there is restriction in the exhaust, there is great extra heat created. The heat can burn exhaust valves, stretch the manifold to turbo studs, and make everything red hot. Exhaust needs to flow freely if you plan to add NOS. I hope you have good fuel with very high octane if you plan to run boost and NOS.

I created an account just so I could say - sixshooter, your posts will live on in history. Thanks for your great info, full and complete sentences, as well as references to specific parts and links.
Awesome, awesome stuff.... now would you mind commenting on my thread I just started :D

fully agree

I'm starting building my Miata today by using this thread as manual

Please come over to Miataturbo.net and post an introduction of yourself in the "Meet and Greet" section. I'd like for my other friends to get to know you and what you are doing. I am also "sixshooter" on that forum.
https://www.miataturbo.net/