Motor Swaps

So, your motor let go, and you're thinking of upgrading. Or, you're just wanting to put a more powerful motor in the car. This is a simple guide to what works and what doesn't.

First off, the ONLY motors that will bolt in are 2nd generation motors into the 2nd generation chassis. Mazda changed their minds many times on how the motor itself bolts into the car, greatly limiting your options.

So, let's go through the swaps and potential swaps motor by motor -

Early NA (86-88) to later NA (89-91) - bolts right in. Intake ports are shaped a little better, and the motor has higher compression rotors. Best to use the newer upper intake manifold as well - it flows better, making for an easy 5-10 hp increase. There is some minor fitment issues, but nothing major.

Early turbo (87-88) to later turbo (89-91) - bolts right in. Again, upper intake manifold is better - you have to have both the lower and upper intake manifolds, though. Turbo and exhaust manifold is a much better design - each rotor has a separate path into the turbo, and each rotor has its own wastegate "tube" for better boost control. The turbo is a bolt-in. The motor itself has the higher compressoin rotors and better intake ports, as well as different spark timing (spark plug holes are in slightly different locations).

2nd gen body, 3rd gen motor (93-95 RX-7) - Possible, but far from easy. The 3rd gen motor mounts are on the back of the engine, instead of the middle. This would require substantial fabrication work. The twin turbos from the 3rd gen simply don't fit - not enough clearance in the engine bay, and they need the 3rd gen ECU for proper sequential control. There really is no good reason for this swap - more power can be made with a turbo upgrade, and a TurboII motor can be built with some 3rd gen components (like the better rotor housings). Motor has same compression ratio as 89-91 Turbo motor.

2nd gen body, 20b 3-rotor engine from Japan - Possible, but FAR from easy. Everything has to be custom - new subframe to fit the motor, new front swaybar, radiator location has to be changed for clearance, custom exhaust, needs aftermarket fuel computer, on and on and on. Only really possible with a LOT of time and money.

2nd gen body, Japanese Cosmo 13B motor - Not worth it. The motor mounts are in similiar location, but the motor does not bolt in - substantial fabrication required. Might be possible to use some of the engine parts in a motor buildup, though. Also, the twin turbo from this motor is similar to the 3rd gen twin turbo - won't fit, needs control system, etc.

NA to TurboII - possible, but not worth it. The price of TurboII's have come WAY down - cars needing some TLC can be had for $3000, with $5-6000 for a pristine model. It's just not worth the time and effort to do, unless the NA in question is super sharp and clean or special in some way, or if it's a convertible (turbo convertibles were not available in the US).

Brian Schiller did a turbo conversion to a Convertible. Here's his list of things to be changed:

It's a lot of work. Like I said in my other post you have to swap the:

1) Engine (With manifolds and turbo)

2) Transmission (The turbo flywheel is different, because the starters
are in different places. You MIGHT be able to get a custom flywheel
made, but the turbo tranny is much stronger)

3) Driveshaft (The transmission output shaft is much bigger, so the NA
driveshaft won't fit. Plus the Turbo drive shaft is .5" to 1" diameter
bigger)

4) Rear Differential (The holes in the end of the turbo driveshaft are
farther apart then on the NA, so it won't bolt up to the NA rearend.
Plus the turbo rearend is Limited Slip, and a stronger differential)

5) Exhuast (The turbo and NA exhausts aren't the same. You can probably
keep the stock NA cat-back though)

6) Hood (The turbo one has a scoop. You could keep the NA hood if you
wanted to go with a front mounted IC)

7) Brake Booster Vacuum Line (This line conencts to the passenger side
of the engine on the NA, and right in the middle of the turbo engine.
Plus the turbo hose has a check valve in it, to protect the vacuum
booster from boost)

8) Metal Coolant Line On Passenger Side (The bracket that holds the tube
for the relief silencer is welded to this tube, and it sits differently
on the two cars)

9) Injector Wiring Harness (This harness is WAY different, a lot more
sensors on the turbo)

10) Fuel Computer (The NA computer doesn't have the boost/rpm fuel maps)

11) Main Harness (This is the one that goes from the ECU, along the
firewall, through the firewall, up to the driver's side headlight,
across the front bumper, and over to the other headlight. This has to be
changed because there is MAJOR wiring differences. For example, the
control wires for the alternator are on the driver's side harness on the
T2. On the NA they are on the injector harness. Where they plug in on
the NA, is where the boost gauge wires attach on the turbo.)

12) Alternator/CAS/Tranny/Battery Harness (The wires in this harness are
longer, and the turbo one includes the alternator control wires, where
as the NA one does not)

The wiring is just too different to try and rewire yourself. Go to your
local dealer and look at the wiring diagrams, there are MAJOR
differences between the NA and turbo.