muy muy interesante:
Differences between revision 1 & 2 engines and revision 3
Just a quick list, do not take any of these as gospel:
position and orientation of oil filter changed.
different internal engine parts, e.g. pistons, con-rods etc.
turbo charger changed from Toyota CT26 to CT20B (same intercooler though).
boost pressure raised from about 10 to about 13 PSI.
power output raised from 220 to 240 BHP.
compression ratio slightly lowered.
injector size increased from 430cc to 540cc.
fuel cut threshold raised from about 12 PSI to about 18 PSI.
head and inlet path completely redesigned. TVIS removed, 8 ‘independent long ports’ reduced to 4.
throttle body increased from 55mm to 60mm.
inlet valve lift increased from 8.2 to 8.7.
different, smarter engine ECU, more tolerant of poor fuel, different connector pin out.
air flow meter removed.
intake manifold inlet air temperature sensor added. i.e. after turbo and intercooler.
ECU now modulates the turbo VSV to achieve variable control of boost pressure rather than either open/full or closed/reduced. Control of boost now quite subtle when ECU is unhappy because of temperatures, detonation, speed, etc.
location of valve shims moved (someone said this was to stop problems with them falling out). If the manual is to be believed, this makes adjusting the valve clearances a much bigger job as on the revision 3 it involves removing the camshafts (might as well replace the timing belt whilst you’re at it).
exhaust valve clearance increased by 0.08 mm (probably. valve clearances is one question I’d like answered direct from Japan. They are probably the same as the UK GT4s, but it would be nice to be sure).
oil pan changed from a one piece pressed steel part to a two piece affair, the upper half being aluminium, the lower half being pressed steel.
No. 1 compression ring now described as ‘stainless steel’ in GT4 manual/supplement instead of just ‘steel’. Oil ring is described as ‘stainless steel’ instead of ‘a combination of steel and stainless steel’. No. 2 compression ring remains described as ‘cast iron’.
idle speed perhaps slightly reduced (need to check this out on a rev 1 or 2 car, my stickers say 750 rpm, I’ve a feeling rev 1 & 2 was 800 rpm).
exhaust part numbers changed. Revision 2 part number for the front pipe is superceeded by the revision 3 front pipe part number. Back-box part numbers different. Unknown to me whether they are actually different.
Coolant drain plug added on cylinder block (on older engines the manual says to disconnect a by-pass hose when changing coolant).
(Please note a lot of significant chassis improvements were already made for revision 2, although revision 3 ABS is probably much improved including the addition of an accelerometer.) Its rumoured that the USA never got the later improved engines, even though the american version of the MR2 turbo was sold there until 1996 (in very small numbers after 1994 though).
Chassis number SW20-0087386 and onwards have the newer engines according to the Toyota Electronic Parts Catalogue for the Japanese MR2 turbos.