from turbo to intercooler.......... and from intercooler to throttle...........
i would just say use a diameter which fits over the turbo outlet and the intercooler inlet........
you wont get any benifit by running a bigger tube as
the turbo outlet hole and inlet hole on the intercooler will restrict any gain from this!
as far as i can see i soppose this is how it would work....
plus at the end of the day the turbo can only ram so much air in the engine.....
you can buy a boost valve which will allow you to run higher boost pressures over factory pressure........ ie keeping the wastegate closed (waste gate is a little flap inside the turbo which controls the boost pressure by opening a flap which allows air to bypass the turbo) the depending on boost pressure.... there is a presure which you can go up to...
ie say standard pressure is 10psi you may be able to run it 1 or 2 psi more without any problems......
but unless its set up to cope with the higher turbo pressure, ie compression ratio, fuel timing, igition timing etc its lible to go bang.......it may first blow the head gasket....or it could blow the piston rings off............
theres some info for you........

ps my bro's mate had an uno turbo and he knew someone who fitted a boost valve to i think it was a montego turbo.....and he unscrewed it all the way

he said it flew up the street and went bang!

fun while it lasted!
