M20
UPGRADES
STAGE 0.5-1.5
The best bolt-on upgrade for any M20 engine is the exhaust manifold. The stock unit is heavy and very poorly designed for a performance application.
For most Stage 0.5-1.5 M20, an upgraded drop-in filter is usually perfectly fine and offers a similar power gain to a full intake system. You can upgrade to a full intake system if you wish.
A cat-back exhaust offers the least gains in comparison to intake and exhaust manifold. 57-76 mm (2.25-3 inch) diameters are ideal, though there is minimal difference beyond 65 mm (2.5 in) diameter. Please consider the weight difference to power gain and decide what works best for you.