Those unfamiliar with MR2s should read the appropriate section in an MR2 engine repair manual describing coolant filling procedures. Bleeding the air out isn't rocket science, but air-locks are a common cause of overheating problems, which could be very serious especially considering the turbocharger is watercooled. Its not a job a DIY mechanic should fear though as long as they are pretty cautious that air-locks sometimes happen. (Warning: never use a mains voltage inspection lamp under the car when draining the coolant).
Original turbos on Japanese MR2s use ceramic exhaust turbine wheels, rebuilt units will use some kind of steel instead - the amount of difference this makes to turbo lag is unknown to me. The ceramic turbine wheels are absolutely slated by turbo rebuilders as being unreliable, but I've not really heard any first-hand accounts from MR2 owners which back this up compared to turbos failing for other reasons such as wear or the oil seals going, and in my experience the ceramic CT20B will stand very heavy use at standard boost pressure; it will just wear out a lot quicker than with normal use. It does however sound like Toyota use steel not ceramic for the UK Celica GT4 turbo, but not for Japanese Celica GT4s (well a 1994 Japanese ST205 had the exact same part number as my revision 3 turbo at least).
I also found it unclear whether other aspects of rebuilt units will be the same as original spec, such as whether the turbine and compressor wheels are matched to the original. One turbo rebuilder had problems obtaining the shafts used in the CT20B but solved this using a thicker one, others may readily try to sell you a CT26 with no mention of any downsides. None of this is an issue for people that wish to have their turbo upgraded in order for it to run higher boost pressures, but there may well be a noticable penalty in responsiveness compared to a turbo highly matched to an engine (and vice versa) by Toyota's extremely large research & development budget.
For price comparision purposes, Turbo Technics and Fensport wanted about 700 pound (inc VAT & carriage) for an exchange CT20B unit ('Turboforce' are also worth speaking to) whilst the list price for a brand new unit for a revision 3 from Toyota GB is 1032 pound (excluding VAT, excluding any discount) (Aug 2005).
A possible myth that exists is that you can check the condition or a turbo by feeling the amount of play on the compressor wheel by hand. A brand new turbo has loads of radial play if not axial play and the service limits for both I think are generous. The real issue is probably whether the wheels are rubbing on the housings, or if they've gone out of balance. You might not be able to feel play in a used turbo because of oil film or something.
Revision 2 onwards: 195/55 15 front, 225/50 15 rear.
These sizes give about the best handling, deviate from them with caution. Minimum speed rating is V. Yokohama were fitted as original equipment and rumour has it Yokohama designed a tyre specially for the MR2. Bridgestone S03s, a once popular choice with UK owners, are no longer available in standard MR2 sizes (Jun 2005) leaving Goodyear Eagle F1 GS-D2s or Toyo Proxes T1-Rs as the most recommended options from owners. Sourcing a specific pattern in both sizes can be frustrating.
Your door sticker should give you more reliable information. Generally you can fit better or, within reason, bigger, but using smaller than the manufacturer's recommendations is probably illegal and may affect your insurance.
Note that theres a particular kind of clip on balance weight for the OEM wheels, probably something to do with European verses Japanese car makers. An uncaring tyre fitter can manage to hammer the more common kind onto the wheel, and it will probably stay on, but it won't fit very well or look right. Note ideally for perfect balancing you'll probably need weights on both the inside and the outside of the wheel. You may still want to request they only use one weight on the outside (as opposed to 2 or 3 smaller ones) for cosmetic reasons. Adhesive stick on weights have a reputation for falling off, but are an option for the majority of tyre dealers that don't seem to have the Japanese weights.
14" Wheels: 29 PSI (200 kPa) front, 32 PSI (220 kPa) rear.
15" Wheels: 30 PSI (210 kPa) front, 35 PSI (240 kPa) rear.
The Japanese door sticker on my revision 3 turbo seems to specify 2.0 Kg/cm2 front, 2.3 Kg/cm2 rear. By my calculation thats 28.4 PSI front, 32.7 PSI rear. However I don't see any reason to use lower pressures than the UK model which is lighter and slower, assuming the speed limiter on the Japanese car isn't operative. 4.2 Kg/cm2 (59.7 PSI) seems to be listed for a 135/70 16 tyre, which I presume is the compact spare? Please note my use of the word seems, I can't read Japanese.
- or at least those are the numbers cast into my stock toyota alloys on my revision 3 turbo. (Revision 1 is different with 14" wheels.)
Currently the second hand value of original toyota MR2 15" alloys is less than 150 pound, probably due to the amount of people fitting 16" and 17" aftermarket wheels for their cosmetic appeal. OEM 14" wheels are virtually given away, sadly.
Note 14" wheels wont fit on the front of revision 2 onwards because of bigger brake disks. Similarly compact spares from revision 1 wont fit later cars. A standard 15" OEM front alloy wheel will fit on the rear of revision 2 onwards cars, and seems to work fine for emergency use but bear in mind that its probably illegal and may affect your insurance even if it probably is a lot safer than a compact spare. A standard front 15" alloy plus tyre weighs about 16 kilograms.