We get numerous requests or engine swaps, mostly using the readily available engine or 1/2 cut packages imported by us or others japan. Having performed a large number of these on Toyotas, we thought it would be worthwhile relating a few problems that have to be solved.
The most common conversion request is the Toyota Gen3 3SG or 3SGTE into earlier model Toyota MR2 ,Toyota GT4 or Toyota Celica. Whilst they look similar to earlier models, and will physically bolt in, all of the 3SG family engines after Oct 93 (identified by oil filter on the sump) require considerable effort to get all the electrics working as they should and look like factory fitments. The biggest advantages of the post 93 engines is they don't use the bulky flap type air flow meter which frees up room in the bay, and they have a better sump system with improved surge control. Of course, the later Toyota BEAMS (NA) engines also are the most powerful due to their VVT and better inlet manifold design and the Toyota Altessa engine changes to coil-on-plug which is great if you want to increase the boost.
These are some of the issues to be solved.
Engine and gearbox mounts differ in details between all the models. Few of the 205 GT4 or 215 Caldina mounts for example, are usable in a 165/185/SW20. The GT4 mount brackets are required for the 184/GT2 conversion. Not all engine blocks have suitable bosses cast in to accept rear drive mounting plates ex SA 63 Celica. In nearly all cases, if the same engine family is being used, then the mounting brackets from the car, can be added to the donor engine. In front or mid-engine use, the engine has only 1 mount at the cam belt end, and these are readily swapped around. The other 3 mounts and brackets all fit onto the gearbox, and you need to correct brackes to for the box/car combination. For example, the turbo MR2 brakcets are different to the NA, but the rubber mounts will interchange (but are not 100% identical)
The wiring harness is totally different between all donor models, eg RAV4 , Caldina, GT4, MR2 etc. This means swapping between models is much harder than it first looks. Certainly swapping any front engined loom into a MR2 is not a job for the feint-hearted as there are significant issues in mating up the body harness. With later donors like the Caldina and ST205, the connections to the body loom, fuse box , fans etc are totally different in concept. When swapping into a GT4 however, It is easier to modify the 185 loom to work the 205 engine, than vice-versa. This is usually the hardest part of any conversion if you want it all to look and work like a factory fitment. Using an aftermarket computer is a common "solution" to wiring difficulties.
The 165/185/early SW20 engines all have features not used in late engines; eg. air flow meter, cold start injector and related sensor. If you use the early loom, these need to be removed or modified for another feature.
Oxy sensors can be quickly identified as single or 4 wire type, screw in or 2 bolt flange mounting. Single & 4-wire types wont interchange, and the ECU is mated to the specific sensor.
The ST185 GT4 requires lots of body mods to correctly fit any 3SGTE with a water intercooler. The intercooler radiator wont fit properly behind a stock front bar. The body has no mounts on the left chassis rail for the pump. The larger air filter from the 205 wont physically fit in a 185 if the battery location is retained. Simple pod filters are disastrous as the air intake temperatures quickly get too high. Mounting the battery in the boot is harder than it looks due to the location of the petrol tank directly beneath. On the 185, the best battery solution is a special thin gel-cell battery and mounted under the seat. On the 204 however, the "conventional" battery can remain when converting to a stock 205 engine and air box.
The MR2 air-air interoolers are marginal at best, and any upgrade should entail a change to this part. I have seen several MR2's retro-fitted with barrel-type water intercoolers , but they generally have too small a front radiator and they are not much better than stock. The front mounted radiator needs to about the size of the air-con condensor, to make it all work properly. This is much easier to achieve on a Caldina or Celica.
The Altessa "BEAMS" engine is a popular starting point for rear drive conversions as they are designed for that. Because they are so tall, custom mounts are needed to get them low enough in the engine bay so the cam cover clears the bonnet. The alloy sump often has to be changed or modifed to clear steering racks/subframes. The back face on the sump has the bolts for the bellhousing and only the 6 -speed box just bolts on. It is not hard to weld in some tubes if you want to use a W series box with a 4Y bellhousing. You can't easily change the sump to the earlier all-steel one, as the oil pump mates to the alloy part of the sump. The starter often has to be moved. The bulge on the front of the cam cover for the variable valve timing, makes fitment into the MR2 a bit challenging, as there is already negligible room in that spot.
The ST215 Caldina engine, despite being the final incarnation of the 3SGTE, is not without its problems, especially if it has been modified. When standard, the only common shortfall is a leaking exhaust manifold and before fitting it to any any car, we strongly suggest the minimum situation is it is removed, ground flat and a new gasket fitted. For the more adventuruous, change it in favour of a Gen3 3 type and all future problems will go away. if you intend to radically increase the boost, then dismantle the engine and change the conrods as they are a known failure point once large boosts are regulalrly used. All of the "plumbing" around the engine requires very minor re-working to make it fit into other models.
If you plan to use an engine with an alloy intermediate sump, then you have to make sure it will be OK for the angle the engine will end up. RAV4, Caldina, Celica, MR2 and Altessa are all slightly different to each other. None of the front/mid-engine sumps are correct for a rear drive car.
Any E series 3S box can be mounted to any 3SG/3SGTE but there are minor bell-housing changes between models, especially oct 93 onwards engines with the alloy sump. Any conversion should try to use the matching gearbox. It is relatively easy to convert a GT4 box back to 2WD if you have some parts and skills in gearbox work. On the GT4, the lower subframe is different and the 165/185 one needs minor re-shaping to clear the 205 sump. Using a non-turbo S code gearbox gearbox with any turbo engine is far from ideal, as they cannot handle the torque.
In front & 4WD cars, axles often need to be swapped or custom made. For example, the later V6 camry axles are not dismantlable and too wide for most older models.
Air conditioning compressors & condensers have numerous different connections, however the top plate on the compressor can often be swapped around to get the fittings you need. Any "old" compressor designed for R12 gas, needs to be stripped and seals replaced with ones suited to mandatory R134 gas. There is a sticker on the compressor saying what it was made for.
There are separate technical articles that should br read.
We are happy to undertake convesion jobs like described, but please realise we are not a free consultancy service. if you want to do it all yourself, then do your own research & experimentation using the above as a guide only. We are unfortunately unable to respond to email or phone requests for free advice on wiring problems, emissions , computers etc., We will gladly undertake tasks you cannot handle and be part of your project, and can then offer all manner of assistance.