Converting your 1.6 Miata to a 1.8

Looking for an inexpensive way to get 200cc more displacement from your Miata? It's not that hard. The 1.8 conversion has been done dozens of times and we still get a lot of questions about it. This is the short version and is not intended to cover all the details - Mazda Miata MX-5 Performance Projects has a full description as do a number of websites. We also have a 1.8 conversion kit that includes all the brackets and wires you need.

Keep in mind that there are three basic types of 1.8 engines. The 1994-97 version is easy to find. The 1999-00 is less common, but has a better flowing head. The 2001-05 heads also have Variable Valve Timing, which is a problem unless you have an aftermarket ECU like the Hydra Nemesis to control it.

If you want to put one of our forced induction kits on a car that's had this conversion, let us know and we'll put together the right parts for you. Flyin' Miata can also do the work for you. We can even go one better and drop in a bored and stroked 2.0 if you want!

What do I need?
1.8 engine with intake manifold
1.8 exhaust manifold or header
1.8 catalytic converter (possibly)
1.8 injectors
1.8 motor mount brackets
1.8 alternator (possibly)
throttle body adaptor
recommended: the FM 1.8 conversion kit
also recommended: new rubber motor mounts, timing belt, new seals.

What do I reuse?
1.6 ECU and wiring harness
1.6 coils
1.6 throttle body
1.6 thermostat housing
1.6 intake tubing

What do I do?
Remove your old engine. Transfer your oil pressure sender and thermostat housing over to the 1.8. At this point, you're also in an excellent position to do a timing belt change. If you have a later 1.6 with the long nose crank, transfer your crank pulley and water pump pulley over as well. If you can't do this, then you will need the alternator from a 1994-97. Do NOT use one from a 1999 or later car. The stud on the 1.8 alternator is a little larger so you'll also have to enlarge the hole in the ring connector to attach it.

Mount the 1.6 throttle body to the 1.8 manifold - we recommend using our adaptor. Make a bracket to mount the coils to the back of the 1.8 head or use our coil bracket. Extend the wiring for the cam angle sensor. Modify the throttle cable bracket (yes, you guessed - we have one). Block off the EGR fitting with a plate. Reinstall the new engine using the 1.8 motor mounts and attach the exhaust. If you want to use stock parts, use the upper section of the 1.8 exhaust and the downpipe from the 1.6. This will let you retain your stock cat although you will have to weld a bung in place for the O2 sensor. If you use a 1.8 header, you'll also need a 1.8 catalytic converter. Use the 1.8 injectors with the 1.8 fuel rail, but all 1.6 wiring including the injector wiring harness. Basically, if it's electrical keep the 1.6 parts and everything else comes from the 1.8.

If you are using a 1999 or later engine, you'll have to mount the CAS to the back of the exhaust cam and put your 1.6 fuel pressure regulator on the 1.8 fuel rail to make it a return fuel system.

The biggest problems seem to center around the intake system. When we do a 1.8 conversion, there always seems to be a turbo system involved. This is the easiest way to deal with it. However, if you're not looking for bulk horsepower, you have a couple of options. If you use the 1.6 thermostat neck and housing, the intake crossover pipe will need to be altered to fit. If you use the 1.8 thermostat neck and housing, you can use the 1.8 crossover pipe - but you'll have to find a way to turn the fan on. The wire to the thermosensor can simply be run to ground so the fan runs as soon as the ignition is turned on.

Back to FM tech