I have a b20a5 and I was wondering what all performance upgrades I can do to it and also I have a lot of b18 parts will a lot of tjem fit this motor and stuff all help greatly appreciated thanks

 

There is a way to get a B16/B18C head on B20A/B21 engines, but I don't know much about it. Involves fabrication and the results really aren't worth it. B20A's have terrible rod/stroke ratios and don't rev well.

A decent amount of people have successfully turbocharged B20A family engines. Several companies make turbo manifolds, then I'd go with an SAFC or perhaps a custom standalone like Megasquirt.

B16 Pistons and H23 Rods can be used to give the engine a stronger base so you can go beyond 5-6# boost.

Modern B-series intake manifolds will fit with a little bit of custom work (drill three holes)

Some people have successfully swapped in H22's. It is difficult and expensive and requires a lot of custom fab and wiring.

Don't expect much aftermarket support with the B20A. it's pretty much all DIY so do your homework.