A bigger turbo will have more lag than the current turbo. Combined with extra fuel your current turbo would be capable of blowing the head gasket. Default is 14-15PSI but it will go a lot higher if you let it (fit a boost controller).
Plus, from what I heard, more than 18PSI wont do any good without a front mounted intercooler.
So, my question for you is: what do you think to gain from a bigger turbo? Or was this a question for the serious performance thread
yeah, to justify i bigger turbo i really think you would need bigger intercooler and bigger fuel pump first (maybe give the derve doctor a ring to confirm this), and then its going to need work to stop headgaskets blowing for england!
the mk1 had a bigger turbo, but dont think there will be anything to gain by putting it on (just more lag).
do an FMIC first then see how you get on from there! (presuming you have already turned the turbo pressure up and tuned the fuel pump)
you dont really need a bigger turbo, just more boost/fuelling, then as said above the F.M.I.C. finishes it off nicely. then somewhere like essex turbochargers can do you a hybrid turbo (same size as standard but much better) for Â£350 for more progressive effective boost
you'd need a uprated head gasket to put a very big turbo on. and its very likely he also had spent zillions of squid on the internals etc. i've looked into prices for uprated internals and head for the TD and your talking massive massive money (Â£3k for the head done properly cos its a one-off). god knows what injectors and pump it was using! for general nice performance upgrades think normal turbo but hybrid, FMIC, big boost, big induction kit and exhaust, decat, water injection, nitrous, and change the gear ratio's.
i ended up ditching project diesel after finding the zetec with a blower responds much better to mods! thats not to say my TD is a slug...
diesels lack power higher up the revs, which is worsened on the 1.8TD by the fact that its single cam 8 valves.
if you do go for a big turbo, i looked into it and i was quoted at least Â£1000 to make a custom manifold and downpipe for the turbo to go on (that didnt include the turbo) and they said as long as i could get the fuelling to go with it then 180-200bhp could be reached. they said with a normal size hybrid turbo i would be looking at 150-160bhp.
also i would add that i've taken both turbo-diesel and petrol cars on several track sessions and i would say that diesels are not much good for on the track given their limited revs power band. you need a petrol with plenty of revs to just keep going and going up the revs.
in a TD you get all the power at once then nothing and have to change gear!
diesels are OK for rallying because short spurts of big boost around the twisties is fine, but for racetracks think petrol.
i'm not dissing the 1.8TD, nobodys stuck up for them more than me and i've done alot of work and research on the subject. but this is the experience i've had with diesels and trackdays.