hello,

i've purshased two 9S heads on ebay and want increasing performance myself on it. my project is to put 4 oversized ( +1mm) FERREA RACING valves machining the stock valves seats, do a light surface improvement on head ports ( not increasing the ports diameters ).

I want also increase compression by milling the heads but i can't find on manuals the max value i can reach. do you have this?

Stock valve seats and heads milling must be made by a local engine professional, here in Switzerland

I'm also planning to put a 12S ( 49mm) throttle body ( std is 46mm).

What do you think about this ?

PS: all this is for a 2005 XB9SX.sorry for my poor english