Solid Thinking

My personal tips on Supra NA-TT Conversion (with JDM Aristo 2JZ-GTE engine) to avoid massive headaches:

Sequential Twin Turbo Tips:

1. Stock Turb replacements: The bad thing is they are small and won’t last long with upgraded exhaust/flow. The good thing is you can get replacement stocks for cheap if you keep your eyes on eBay etc as there are a lot of Supras being converted to singles or turbo upgrades. The bad thing is some of them are already knackered.
2. Crack around turbo wastegate: Stock turbo exhaust housing is prone to cracks around the wastegate, and is usually accompanied by louder-than-usual whistle upon spooling. This is a hit-and-miss, and you may be OK leaving it as it is. Worse scenario results in boost leak and inability to perform (e.g., your 1st turbo may not reach good boost of around 7-10 psi). The main problems of replacing the exhaust housing are (1) dismantling the twin turbo assembly (huge PITA!) and (2) disassembling Turbo #1. I am not qualified.
3. Sequential Twin Turbo Actuators: some of the actuators (VSV or the Actuators; for IACV, EBV, EGCV, etc) may fail in older engines. The most common problem is no #2 turbo boost (e.g., turbo #1 spools fine until 3500-4000 rpm where the boost drops and refuses to go back up, accompanied by tractor-like engine sound). This means the valve to #2 turbo refuses to open, so the turbo #1 gets overworked and excess exhaust gas simply gets vented through the wastegate. Replacing the actuators may be cheap (although Toyota does not sell them individually) but taking the twin turbo assembly apart is a huge PITA! Check the VSVs by blowing a low pressure air into the hoses. NOTE: blowing a too-high pressure for testing may actually damage your actuator’s diaphragms. If I remember correctly 7-10psi is the max.
4. Sequential Twin Turbo plumbing: first thing to check if there are any issues is to follow the sequential twin turbo diagram and make sure everything is plugged into where it should be. <PICS!>
5. Exhaust: Straight-through exhaust may be considered as an upgrade. Increased flow may result in increased boost, which would give increased power (my exhaust is a straight-through steel, which increased the boost to 1bar, giving 280kW on axle). Bear in mind the Japanese Spec turbos are weaker than the US spec, and may not last on increased boost for too long.

Cooling system:

1. Water pump: Supra and Aristo water pumps are different. Aristo water pump does not support Supra’s clutch fan. There are some tips on using Supra water pump front assembly coupled to Aristo rear assembly to be able to install the Supra clutch fan, but I cannot verify this.
2. Radiator: Supra original radiator is already bordering on sufficient cooling capacity. It may be enough for NA engine, but put a forced induction system in and the whole equation becomes unbalanced.  If you do NA-TT conversions for looks only then it may sufice, but if you go on boost then sooner or later (and I mean Sooner!) your car would overheat and may bust the engine. Avoid this huge-dollar-figure risk and invest $500-$600 in good radiator upgrade. Tripple core aluminium rads should be in your budget.
3. Cooling fan: don’t go cheapo on cooling fan as Twin Turbo gives out a lot of heat. A lot of people swears their life on the standard clutch-type fan which can flow in excess of 3000cfm, and complete standard fan shroud. If you do decide to go electric fan, double fan is a must. Good double-fan shroud would greatly help minimise your overheating risk.
4. Coolant lines: your engine would most likely be “properly aged”. Coolant lines’ interior may collapse without any visible exterior signs. As I have just experienced, one of the turbo coolant return line simply burst upon parking: the inside wall seems to have been eaten by something sinister. Replace all your coolant lines, preferably while your engine is still out of the car.

Electronics:

1. Fuel controller: Using stock TT Supra ECU is fine, but unexplainable complications may occur. In my case the car ran excessively rich. Not only this wastes petrol but also risk running the fuel down the piston rings and washing the oil layer lubricating the cylinder wall (long term risk: busted piston rings). We installed SAFC (Neo) and dyno tuned the car. Not only we managed to reduce the A/F ratio, but we also gained a whole 20kW on the rear wheel. That’s about 7% power gain for my engine.
2. Tachometer: NA tachometer may not work with TT ECU and Ignitor due to the different signal type being used (also to do with the distributor-based ignition on NA and Coil Over Plug digital ignition on TT. NA tacho runs on high signal level while TT tacho runs on low signal level. As such, NA tacho would not be able to move/detect the low signal level produced by the TT ignition system. To solve this, take apart your tacho unit and bypass the 33kOhm resistor (in one of the corner of the circuit unit) by wiring the two legs together (this is the only mod I needed to do). For some people this did not solve the problem, and they needed to also hook up the wire from the TT Igniter A1 terminal (ext) to the blk/wht wire on the Diag connector (tach) and your good to go (see more on this source).

Miscellaneous:

1. Crank dampener pulley: check the crank dampener pulley to make sure it is flawless. The pulley consists of two parts: steel pulley and aluminium center inserts. If there are imperfections, the pulley would become imbalanced and the inertia would easily fracture/crack the aluminium part. On mine there was a small chip on the outer edge, which upon closer inspection apparently has caused massive cracking on the aluminium center. This is a timebomb and when it does explode you’ll be walking. Search for “Crank walk” on Google to find out the worst case scenario.
2. Installing gauges in the interior: there are two ideal places for installing gauges on the stock Supra dash without any modification. A 60mm gauge can fit inside the center air vent (a ring using suitable 5-10mm rubber hose may be required) if you remove the air vent globe. If you are feeling adventurous, you can dissect the air vent globe and fit the gauge in it instead (which gives you the ability to swivel the gauge for better view). A 52mm gauge can fit (very straightforward) into where the clock is.

Some more information on the required parts here courtesy of mkivsoopra.com and here, courtesy of mkivforums.com.