Cheap engine upgrade for AUDI Coupe and Audi V8.

[Stas Ivanov <ctas@carry.neonet.lv>]

Hello!
At the moment i'm reading various autosport magazines and they offer some
upgrades e.g. air intakes with cone filters , exhausts,headers. They claim 
if i change air intake i can get extra 10 hp. Is this true? 
What cheap upgrades can be done to Coupe 2.3  and V8 3.6 for gaining some
extra power ?
What are the weakest parts of audi engines which must be replaced ? 

Stan
Audi Coupe GT 2.3
Audi V8