hya mate and welcome to the site, loving the supra tt, especially vvti very rare, must be a 1998 or newer Would of loved to have got one but age was a factor for me. Stunning looking cars never the less and rapid... but sure you know that lol. Okay lets see if can help you out here I have a UK spec but this question gets asked alot quite a bit.
1.
What are the SIGNIFICANT differences between JSPEC and UK SPEC?
Depends what spec you go for on the Japan spec, you can pretty much get the same set up as the UK, only major difference is that the Imports are limited to 120 but this is easily eliminated by a HKS defender, and if you tune it you can get a higher top end than what the UK one is capable off. The only other differnece is that the fuel tank is slightly smaller but no biggy from what I hear Brembos, leather seats and GT pack are all optionals on the Imports, mainly standard on the UK.
2.
What are the standard wheel sizes for both?
Hmm Im pretty sure they are both 18", although have heard of some jap cars coming with 17"
3.
Ideally i would like to put wider wheels on. What is the limit without big modifications.
Well Im running 10.5 x 19 rear and 9.5 x 19 front with toyo tyres 285x30x19 rear and 265x30x19 front, Cavey is running 12 x 19 which are mahoosive, bith of these set ups are without modifying the arches. Important thing is the offset of the wheels must clear the bulky brembo callipers. If I lowered my car then like any othercar my arches would have to be rolled
4.
Is there a basic performance upgrade. On supras we call it BPU (Basic power upgrade). It is essentially a stage 1 engine modification. This includes full de-cat with restrictor ring, exhaust, dump valve, fuel cut defender, uprated fuel pump, cloder grade spark plugs, boost guage.
I was wondering if there was someting similar you guys do on the Z? If so, what power/torque outputs result?
You can get an Fcon IS HKS which will allow power gains from exhaust plenum induction, but the ecu is self learning and will eventually set itself back unless a 2003 model below I think. The only way to get the more power gains is to go FI, but if you are looking at anything over 400bhp then an engine rebuild is highly recommended.
5.
What are your average MPG's? I'm hoping tey may be a little better than my supe!!!!!
I currently get about 24mpg but as you know its all about how you drive, and for the first 3 months Id say youd probably do 16-18
get some piccies of you car mate would love to see it