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 . We also have a more complete version. Some problem-solving abilities will be required.
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 motor mount brackets
1.8 alternator (possibly)
throttle body adaptor
recommended: the FM 1.8 conversion kit
1.8 thermostat housing
1.8 intake tubing
also recommended: new rubber motor mounts, timing belt, new seals.
What do I reuse?
1.6 ECU and wiring harness
1.6 throttle body
What do I do?Remove your old engine. Transfer your oil pressure sender 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. If you use the unregulated 1999-05 alternator your battery will overheat and you will likely damage some of your car's electronics. 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. This is not necessary if you're using a Hydra Nemesis. In fact, if you are using different engine management, you may want to keep the 1.8 throttle body due to the improved throttle position sensor. Check with your engine management supplier.
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. If you use a 2001-05 intake manifold, you'll need the fuel rail from a 1999-00. Or a Flyin' Miata one.
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 if you are still using the stock 1.6 ECU. If you're using an aftermarket ECU such as the Hydra, you can convert the fans to ECU control.
It is not worth the effort of trying to transfer the wiring and ECU from a later car into the 1.6. This is especially true of 2001-05 cars which will give you fits with the immobilizer system.