why 3,9Ltr?..for reliability....with 4,0L or more you will have   problem (probably) with the crankshaft.....i had also a 3,9Ltr kit in my GT3 with Mahle pistons...tuned by kraus-systems and Evotech in germany...i dynoed 492bhp in MAHA in Germany...cost?easily more than 20,000euro......