What engine mods can be done without tuning, and what is the computers tuning capabilities?

 

Generally the ones that don't improve performance.

bolt-on stuff like intake and exhaust manifolds can shift or broaden the torque peak within the capabilities of the stock ECU. If done well the effect is noticeable but nothing special.

There are things that can be done to aid in the durability of the engine which allows it to be driven hard more often and with impunity. But the low hanging fruit of regular, by-the-book maintenance should be prioritized.

 

Cold air intake, header, exhaust manifold, clutch, flywheel.
the computer alone has no tuning capabilities unless the computer itself is modified with a chip, or an aftermarket piggy back adjuster is used such as the Apexi AFC.

 

It is also possible to turbo charge or supercharge an engine and not tune it’s computer, but add a fuel pressure riser such as the Vortec FMU to increase the volume of fuel sent to the engine that is needed for a low boost application. I used a Vortec FMU on a stock computer for two years, then sold the vehicle.