Does the ltg 2.0 turbo engine fit on a pontiac firebird (third generetion)

It could be made to work and this engine is available as a crate engine but I would pick something else like a V8. This would not be my first choice to power a heavy car like a Firebird.

This would be a lot of added work rather than just selecting one of the many crate engines that would fit in this car with little fitment issues. The 5 liter V8 or 3.8 liter V6 are the best base engines to consider but you can go bigger or smaller. As FOR said, the V8's available give you good power and reasonable mileage for these cars.

I know but here in Greece we have big taxes on cars based on the cc (think for my fox body i was paying 1500euro just to have it without warranty and gas)so i look an alternative engine with maximum 2999cc and more than 250hp.

Sorry, I did not realize you were outside of the USA. Maybe your smaller engine would be fine in your application. Good luck.