What added BHP would you get from a saxo Vtr with a good cone filter and a full system from Manafole back

extra 20 BHP max with both mods!!

Yeah, 15-20 bhp max

+5% for exhaust
+2to3% for filter

Please do not listen to the 15-20bhp brigade - they r talking utter rubbish.

The conservative estimate without a full PROFESSIONAL ECU re-map is about 2-3% for a GOOD filter / induction kit.none of that cheapo 'max power' stuff.it can lower ur power. Changing the full exhaust system might gain u another 5% if u take the 'cat' off.makes next to no difference (except more noise) if u keep it (legal) with the catalytic convertor on.You WILL need to put the cat back on for the MOT - no ifs - no buts, instant fail if it is missing.

Why bother ? get a real car

Manafole? Is this a French term?
Manifold is probably more like it!