Changing the engine from one manufacturer to another in a car is not a small job and incurs both risk and considerable extra expenses that would not occur if you stick with the OEM engine block.
14500RPM, the reason people only put 4 pot engine in VXes is becuase they only have small engine bays which would be hard pressed to take even a V5 let alone a V6 transversly, with a gearbox that aligns the drive shaft correctly.
Winstar is right about the Americans making huge power, some of Ecotec blocks (ie Z22SE family) make 1400+ BHP on methanol and 800+ BHP on regular 91 octane pump fuel. If you are genuine about wanting more power, try having a good read of these sites for some background info:
1/ 800 BHP General Ecotec link: HERE is a link.
2/ 1450 BHP Ecotec engine link: LINKY_2
3/ Ecotec build book: LINKY_3
After reading that from cover to cover, you should realise that putting an Audi TT engine in your VX will be underpowering it!! IMO stick with GM (ie Vauxhall) all the way, they have been doing it for far longer and all importantly they do it more prolifically for 1/2 the price. Though I haven't priced it up accurately, I bet you could buy all the parts for a 800 BHP engine for less than £7000... put that in your VX and go for a drive against any TT engined car and I will place a bet on the VX winning.

As for Honda engine, I don't know much about them, so can't comment on them really.
Hope that helps

Edited by Nev, 20 April 2010 - 05:07 PM.