Swapping an 86-88 (s4) engine into an 89-91 (s5) car (s5 & s4 swap)
Many people have the desire/opportunity to use an early engine in a later car. It is rarely worth the work. It is MUCH easier to simply find the proper engine for your car and bolt/plug it in. Note that some of these swaps have differences in emissions equipment/passages which prevent being able to keep the car emissions legal when doing so. You’d usually wind up removing the whole emissions rack and components to get everything back together properly, though it could be possible to make such a swap pass.
When doing such a swap, it is important to note that the flywheel must be obtained/used that matches the engine block you’re using. For instance, if you’re putting an s4 NA block into an s5 NA car, you must use an s4 NA flywheel with the s4 NA block; using the s5 NA flywheel from your old block will throw the new block out of balance.
These swaps are really pretty simple in theory, but it takes several hours to get everything swapped over. Basically, you’re going to keep everything that used to be on your original block, and transfer it to the new one. The only times this principle does not apply:
1)the flywheel must match the s4 block
2)it’s much easier to leave off the emissions rack, so don’t use either one
3)if a part on the newer engine is superior to one on the old engine (such as s5 NA intake set, or s5 turbo set)
4)the temperature probe on the rear iron, will only fit the block it came from (the holes are different sizes for s5 and s4)
Remember that anything electronic, or anything that an electronic part bolts to and would not otherwise bolt to on the older setup, must be retained from your old engine. Your car still has to think it is an s5, even though it has an s4 block.
The hardest part of the swap, and the part with the most potential for screwup, is the front cover. The oil metering pumps differ between s4 and s5, and the front covers differ to accommodate this. When swapping front covers, it is possible to allow the bearings and spacers to slip on the e-shaft, doing internal damage and creating a lot of endplay and vibration. For more information on this, see the mazdatrix how-to section (www.mazdatrix.com). Also note the front cover o-ring (oil passage) which is easily lost/crushed/slipped out which will result in loss of oil pressure, so special care should be taken to ensure that this gets re-sealed well. Mazdatrix also has a nice writeup on this.
Now, here is an overview of how to proceed with the swap.
Strip the s5 engine down to the bare block, leaving the flywheel on, but removing the front cover. Repeat for the s4 engine. It is always easiest to simply use all the s5 parts.
Take everything that came from the s5 engine and put onto the s4 block.
When installing an s5 NONTURBO intake manifold on an s4 block, note that you must grind off some metal on the rear iron to allow the middle intake to sit flush with the lower intake. The s4 rear iron is cast slightly taller than the s5 that the intake was originally on.
Note also that the s4 EGR passage must be blocked off for use with an s5 intake. I cut my own blockoff plates from 1/8” aluminum, or you can buy them at places like mazdatrix or racing beat.
Again, the aim of this is to make the car/ecu think it still has an s5 engine, by keeping all the “smart” parts, which are the electronics, from the original engine.
The same principles can be used for s4às5 swaps, and these actually have a bit of merit since a) the s5 engines had higher compression so you can gain a bit of hp and b) the s5 engines had a few parts that were upgraded and though the swap might still not be worth the work involved, at least some improvements can be made. Doing the s5 & s4 swap, is going backwards to a lower compression/lower power engine.