Once you do the usual filter and exhaust then manifolding, both inlet and outlet is a big restriction above 150bhp

Cam timing and lift is the main area of gain then manifolding then really you're looking at throttlebodies etc to get the bigger numbers

Have a chat with Shawspeed to see what cams you need but be aware that n/a tuning isnt as cheap as chipping a turbo!

I have had the 1.6 zetec se from the fiesta zs mk5 at a tad over 160bhp with shawspeed ss4 cams, heavy duty rod bolts, piper exhaust and 4-1 manifold and an omex ecu as we couldnt figure how to raise the rev limit in the standard ecu...all on the standard plastic inlet, but the inlet was a big restiction

The 1.7 will take similar mods