When buying a turbocharger for Nissan Altima 25 liter does it have to be the whole system or can just alone.?

It depends on the specific turbocharger kit you purchase for your Nissan Altima 2.5 liter. Some turbocharger kits include everything you need to install the turbocharger, while others may require you to purchase additional components separately. Generally speaking, a turbocharger kit will include the following components:

- Turbocharger

- Intercooler

- Piping

- Charge pipe

- Downpipe

- Wastegate

- Blow-off valve

- Oil lines

- Coolant lines

- Mounting hardware

- Instructions

If the turbocharger kit you are considering does not include all of these components, you will need to purchase them separately. It is important to note that some turbocharger kits may not be compatible with your specific model of Nissan Altima, so it is important to check the fitment before making a purchase.