MiataPower: 1.8L engine swap into a 1.6L chassis

Updated 8/10/98 1.8L Engine Swap Written by Tom Lamano

I've just completed a 1.8 engine and wiring harness swap into my 91 base model (along with installing a FM turbo II kit) and thought I would document and share my experiences. These observations were written down over a three month period whenever I felt it was important to do so, so its not very organized.

Last winter, I re-read Randy Stocker's article in Miata Magazine and after communicating with Randy I felt confident this was a project I could handle. I set out to find a 1.8 engine, at first considering a 1.8 out of a 91 Ford Escort with just 5k miles. It's the same engine as Mazda's 1.8 and the price was right. However, after calculating the cost of the parts necessary to convert it from its front wheel drive configuration to the rear drive Miata configuration, I felt it was no longer cost effective. I still think this is a good source for 1.8 engines, but only if you already have another Miata 1.8 engine to cannibalize for the necessary parts. I ended up buying a 1.8 from a 95 Miata with 8k miles. I bought it from Mazda Toyota Recyclers (800-628-0918 ask for Richard) in Oregon for a reasonable price and had it shipped to my driveway in Charlotte, NC. The engine arrived in perfect condition, I highly recommend Mazda Toyota Recyclers for anyone's used parts needs, I've used them many times with no disappointments. At first, I was going to approach the swap the same way as Randy, i.e. use my 1.6 wiring harness, ecu, and throttle body. My car was Sebring supercharged at the time and I was going to install it on the 1.8 as well. I began reading about the power output of Bill Cardell's FM turbo/ecu kits and decided to sell the supercharger and get some REAL power. Bill had another customer doing a 1.8 swap and FM turbo install so I didn't feel like the Lone Ranger. That guy soon sold his car and stopped answering my emails so it was Hi-O Silver after all! I ordered my FM turbo kit in mid-March, at that time, I was going to use the 1.6 FM ecu. Bill suggested I put in a 1.8 wiring harness so I'd be able to use his soon-to- be-available 1.8 FM ecu with built-in knock detection and boost control along with superior sequential port fuel injection. I took a look at the dashboard removal section of my Miata Enthusiast's Guide and decided to take the plunge. I called Mazda Toyota Recyclers and asked about the wiring harness from the car my 1.8 engine came from but was too late, it had already been sold. This would come back to haunt me later, as you will see. Luckily, I was able to track down another harness locally at R & R Sales and Service (704-892-4869). I went over to talk to the owner Ron Young, the harness Ron had was in a front end wrecked 95 Miata, with an unusable airbag system (deployed bags). I planned on removing my airbag and installing a Momo competition wheel anyway so I made a deal with Ron where I swapped him my airbag for his 1.8 wiring harness with the condition I remove it from the wreck myself. I practiced on my car first by removing the dashboard, it took about two hours. I had a week's vacation scheduled the next week, and went over to Ron's place on Monday morning. We drove over to his storage yard and flatbedded the wreck over to the shop. It took me about and hour to remove the dashboard, and another 3 hours to remove the harness. I labelled everthing and took lots of pictures. I also removed the dashboard harness from the wreck after determining it was going to be required to match up to certain connectors on the main harness. I ended up buying the 95 instrument cluster from Ron to complete the electrical package. Here are some dashboard removal tips:

Remove the glove compartment before removing the dash, this will allow easy access to the electrical connectors and climate control cables that need to be disconnected.
Remove the console and center portion of the dash which houses the climate controls and radio. Spray some WD-40 into the sides of the eyeball vents before pulling them out via the string or wire method.
Disconnect the two climate control cables to the left rear and right rear of the center section of the dash.
Remove the lower steering column shroud, this will give you access to the electrical connectors below the dash that have to be disconnected.
No need to remove the steering column, just remove the two retaining bolts and push the column down.
Put duct tape on your directional and windshield wiper stalks so they won't get damaged when the dash is lifted over them.
The dash is a tight fit, you will have to exert a bit of force to free it.
Once its free, don't immediately lift it out, be sure you've not missed disconnecting any electrical connectors.

The next day, I pulled my 1.6 engine without the trasmission, which seemed easier at the time, but made installing the 1.8 more difficult. I recommend removing the engine/trans as a unit, those top two bellhousing bolts are a bitch to remove with the engine in the car. The next day, I removed my 1.6 wiring harness. With the dashboard and engine out of the car, this is an easy task. I now had the two harnesses spread out on tables in my garage,two engines sitting on the floor, and the dashboard sitting on my dining room table! My car would have looked more at home in a junk yard.! I spent the following day making minor repairs to the 1.8 harness. The headlight and sidelight connectors on the driver's side were badly damaged from the wreck, so I spliced in the connectors from my 1.6 harness, they were the same type. The next day, I put the 1.8 harness in my car. Most everything fit fine with these exceptions:

The 1.8 ecu harness is longer than the 1.6 harness since the 1.8 ecu is behind the passenger's seat on 94+ Miatas but is in the passenger footwell on 90-93 Miatas. There is however, enough room in the footwell cavity to coil up the excess ecu harness if your car does not have ABS.

The connectors attaching the driver's side end of the main wiring harness to the harness going to the rear of the car were incompatible. My rear harness expected one connector, the 95 harness had two connectors neither of which matched my 91 connector. After consulting the wiring diagram, I determined there were extra wires going rearward from the 95 harness that were not in my 91 rear harness. My car is a base model, practically optionless except for a/c. These extra wires were for the driver's seat speakers, rear window defogger, power antenna, etc. Ron Young let me remove the matching connectors from the rear harness of his wrecked 95 and I spliced them into my car's rear harness. The extra wires that did not match up were just taped off. Right about now you're probably realizing how important it is to have the 1.8 wiring diagram. IMO, it would be impossible to do this swap without it. I got away with not buying the 1.6 wiring diagram because Mike Hayes, the service manager at Montgomery Mazda (704-563-1510) here in Charlotte, was good enough to let me look at their manuals . Budget in another $50 into your engine swap project and buy the 1.8 wiring diagram. BTW, Montgomery Mazda has the best service department I have ever used. They replaced the timing belt and front crank seal on my early 91 (weak crank) 14k miles ago and I never had any problems with it.

The 1.6 a/c relays connector did not match the 1.8 wiring harness. Sometime after 1991 (1994?), a separate small a/c harness was added to the front of the engine compartment on the passenger side. I was able to get this harness and relays from Mazda Toyota Recyclers. The connector going to the a/c pressure switch did not match though, so I spliced the 1.6 connector into the newly acquired a/c harness.

The wiring harness connector going to the coils harness on the 1.8 engine did not match. The main wiring harness connector had 4 pins, but the coils harness connector was a 6 pin type! My wiring diagram showed the 6 pin connector. I drove down to Montgomery Mazda and looked at the 94 and 96 wiring diagrams. It turns out, Mazda changed over to the 4 pin connector and different coils in 4/95, so I had a wiring harness from a car built during or after 4/95, and an engine from a car built before 4/95! Fortunately, Ron Young let me swap my coils harness and coils with his 95 wreck. The moral here is get your wiring harness from the same car the engine came out of.

I tried to mount the 1.6 crank pulley on the 1.8 so I could use the 1.6 alternator, but it wouldn't fit. My 1.6 engine is one of the early ones with the weak crank. The later style may fit, but I ended up buying a used 1.8 alternator from another fine recycler, Mazda Recyclers in California (916-635-5900). The 1.8 alternator is physically larger than the 1.6 which must mean its more powerful due to more windings. I did have to widen the alternator harness ring connector with a drill because the mounting bolt on the 1.8 alternator is larger also. If you decide to use a 1.6 alternator, you'll also need a 1.8 mounting bracket.

The 1.8 went in with help from my friend Wayne Walling. As mentioned earlier, I left the transmission in the car when removing the 1.6. This made putting the 1.8 in very difficult. It took us an hour to finally get it seated properly. We ended up having to remove the driver's side motor mount to get the engine in. Mounting the starter and tightening the bellhousing bolts was tough also. Much of this could have been avoided by removing and installing the engine/trans as a unit. BTW, the 1.6 starter motor mounting bracket does not line up with the hole in the 1.8 block. It must be replaced with a 1.8 bracket. Roebuck Mazda has them for $11.

I swapped my 91 speedo, oil pressure and gas gauges into the 95 instrument cluster for these reasons:

My 91 has a 4:30 rear end ratio, 94+ cars have a 4:10 ratio, I wanted my speedo to be accurate.
The 91 oil pressure gauge is more accurate than the idiot 95 gauge. BTW, you must also swap the sending units.
My 91 has a smaller gas tank than 94+ cars using the 91 gas gauge insured accuracy.

Some of these swaps may not have been necessary, but I really didn't feel like experimenting. I took the opportunity to clean up my audio system wiring at this time. The place that installed my cd player 4 years ago really butchered my factory wiring. replacing the dashboard harness allowed me to eliminate the butchered wiring and replace it with a plug compatible Mazda specific harness purchased from Autozone for $8.

When I installed my Momo wheel after re-installing the dashboard, my horn would not work. I discovered the horn wire attached to the clock spring connector behind the steering wheel first goes to the airbag connector on the passenger side of the car. Since my car does not have a passenger side airbag, this connector is not used therefore the horn wire signal ends there. This connector is was not accessible with the dashboard now reinstalled so I routed a wire directly from the horn relay in the engine compartment to the clock spring connector horn wire. Problem solved.

The a/c compressor is now closer to the front sway bar. I was able to give it more clearance by loosening my JR sway bar mounts and sliding them forward in their elongated holes. I now have 1/2 inch of clearance between the sway bar and a/c compressor. My a/c is presently not working due to low freon, I'm thinking about converting to R134A, someone told me you need to swap the receiver/dryer to do it however.

Here are some other points to remember:

Buy the engine and all the parts necessary to do the swap at the same time, going back to the recycler later will be more expensive.
Buy the wiring diagram manual for the year car your 1.8 engine and wiring harness came out of.
Be sure the engine and wiring harnesses came out of the same donor car.
Give yourself plenty of time to do the swap, I did it over a period of three months mainly because I was waiting for my turbo to be delivered.
Pull the 1.6 engine/trans as a unit, it will be much easier to work on it out of the car and will make installing the 1.8 a LOT easier.
Buy only Mazda radiator and heater hoses. They're pre-formed to the correct shape, will not kink, and take up the least amount of room.
Label and bag everything and take lots of pictures.
Most, if not all the electrical connectors in the wiring harnesses are different, thus making it very easy to connect everything correctly.

Here are some observations from my FM turbo installation:

No need to cut off your stock fuel injector connectors. They come apart very easily by first removing the white plastic retaining clip with a small screw driver, then pushing the metal connectors out the back while raising the tiny plastic tab holding each connector in place. Place some shrink tubing over each metal connector and push them directly onto your 560 cc injectors using needle-nose pliers. The fit will be very tight.
My air filter did not extend completely into the cold air duct, I drilled two new mounting holes for the duct further to the right to allow the air filter to extend fully into the duct. Access is limited from below to thread the nuts onto the mounting bolts. Try gluing the nuts to your middle finger with contact cement to help you reach the bolts from underneath. I've used this technique in many situations where there is no room for two fingers much less two hands. Putting some on the tip of your screwdrivers to help start screws in tight quarters works great also.
I filed a slot in my ecu housing for the keypad cable so the cover can be screwed on completely without damaging the cable. Since the housing is aluminum,it only took five minutes.
All the exhaust manifold nuts are accessible with a standard 14 mm wrench from above and below despite what the instructions say. I think they were originally written for the 1.6 kit and modified for the 1.8 kit.
My cold air duct hits the hood when its closed, I put a piece of vinyl door edge trim on the duct edge to protect the powder coating.
My tach does not work. Bill says its because the ecu was designed for 94 and early 95 engines. The coils having changed in 4/95 (see above). Link is working on a fix. Bill Lackey has gotten around the problem by designing and building his own driver circuit.
I have a backfire in the intake when turning the key on after leaving the car overnight, Its scary, but Bill says its harmless and Link is working on a fix. I mounted a fire extinquisher on my Hard Dog sport diagonal bar just in case.
My car smokes occasionally after a spirited run, probably due to not enough slope in the turbo oil return line. I'm going to put a 90 degree fitting in the line after it exits the turbo to increase the slope.
I haven't done any ecu tuning yet because of the inoperative tach, but my a/f gauge reads rich all the time, even at idle.

Here are some additional mods made during the swap:

Installed a Moss oil cooler to the right of the passenger side grill area, in an inverted postion. This required shortening the oil lines going to the cooler and using 90 degree BPS fittings. I got the fittings from B.A.T. in Florida, they advertise in Grassroots Motorsports. I also had to fabricate a mounting bracket.
Replaced my radiator with a two row automatic unit, cost $125 locally.
Installed a FM kevlar clutch and have just over 900 miles on it now. It engages close to the floorboards and has a little stronger pedal feel than the centerforce it replaced. I haven't done any hard starts with it yet.
Installed a FM turbo exhaust and hi flow cat, very high quality and good fit.
Installed a Cannon rear suspension brace. Initially it interfered with the turbo exhaust but I was able to clear it by bending the exhaust system mounting hooks.
Installed a Hard Dog sport rollbar with diagonal and harness bars. The hardest part of this job was cutting the interior trim pieces to fit around the bar.
Installed a Greddy strut tower brace. Earlier versions of this bar may have been poorly made, but mine is very good. I did have to polish the end links on my bench grinder polishing wheel however. I also painted the mounting brackets silver to better match my car. The bar costs $100, and is well worth it for looks alone.
Had my cam cover polished locally, cost just $50.

On the evening of July 8, 1998, I put in Mobil-1 and coolant, connected the battery, reloaded the default values into the FM ecu and turned the key. The engine started on the FIRST crank! We took the car off the jackstands and drove around the neighborhood (sans hood). That's about it, its been on the road ever since (with hood). This was the most involved automotive project I've ever attempted, but it was not difficult. Being just a hobbyist mechanic it was slow going at times. I'd probably starve if I had to make my living as a mechanic. I hope this helps anyone else who might be considering a 1.8 swap; if I can do it so can you. I'll be out on the interstate trolling for Porsches, but feel free to contact me if you have any questions.

Regards,

Tom Lamano