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Miata Cubed

Engine Swap Adds Displacement to Early Cars

published in Grassroots Motorsports January 1997, page 50.
Note: as far as we know, this is the first 1.8 swap and it contains lots of good information. Since the time it was published, there has been a lot of progress on this front. Flyin' Miata now sells conversion kits to make the job almost painless.

by Randy Stocker

My C Street Prepared autocross Miata was highlighted in the 'Your Cars' section of the Sept/Oct. 1995 issue of GRM. At that time I was quoted as saying that I was thinking of swapping in a 1.8 liter motor into my early chassis to get more usable torque output, mainly because the 1.6 motor had none. Such as swap is legal in Street Prepared, since all Mazda Miata's share the same listing. Actually completing the task is not so simple.

I was apprehensive about the swap because I knew that the computer and wiring harness had completely changed for the 1.8 and I did not know if the long block would even fit the 1.6 transmission or subframe. It didn't help that many people told me that it was not worthwhile and even possible. But I persevered, and found that this swap not impossible, though not a job for the faint at heart. It took three weekends of solid work, about $1,500 and some fabrication, but I did it. Randy, Mike, and Steve at Mazda Competition were all a big help at settling my fears about various things and getting me little miscellaneous parts I needed.

The project got rolling when I saw an ad in SportsCar placed by ITA racer Phil Finkle, who was selling 1.8-liter Miata motor. It was an old ad, so I knew the engine was probably sold, but I wanted to inquirer about his source to see if they had anymore. Finkle said he still had the same motor in his possession and wanted to sell badly. So, I gave him the requested dollars and he crated and shipped it to my engine builder, Andresen Engine Development in Crystal lake, IL.

The motor only had 13,000 miles on it, so all I budgeted for was a refreshed head. Andresen got a late start on freshening up the head (they had 11 Formula Fords running at June Sprints), but once done the head sported fresh valve job, .004" shave, and gasket matched intake and exhaust ports.

Since this motor had sat for quite some time, I decided to have the injectors cleaned and flow matched at Leo Franchi's MidWest MotorSports while the motor was being worked on. I don't know if this is an accurate representation or not, but the 1.8 injectors flowed about 45 percent more than the 1.6 injectors did (95ML for 12,000 cycle vs 105ML for 9,000 cycles, both at 40PSI). Interesting fact.
UPDATE 12/2/98
The 1.6 injectors flow 205cc and the 1.8 injectors flow 230cc, the information I had back in 1996 was based on an appearently miscalibrated flowbench test.

Now it was time to actually install the engine. (thanks are due here to my Windy City Miata Club buddy, Mark Klauer, who brought over his engine hoist for me to borrow). I had already made large investments in 1.6 performance parts, such as a Centerforce 13lb flywheel, Rod Millen computer chip and Racing beat exhaust header; I hoped that they would fit so I wouldn't have to buy all new components. I found out that the 1.8 long block is really just a stretched 1.6, so the 1.6 motor mounts, transmission, alternator, starter, flywheel and clutch fit perfectly. All of the coolant hoses hooked up too, once I studied the cooling diagrams of both manuals and figured out were they all went. For example, the 1.8 comes with a water-fed oil cooler and the 1.6 does not, making things less than straitforward.

The motor did not come with a computer or wiring harness, so I decided to use the existing 1.6 engine control computer (with the Millen chip) and flow meter. Consequently almost nothing electrical mated up, although most of the sensors from the 1.6 screwed into the same locations on the 1.8.

The only wiring harness adaptation that was required was to lengthen the wires going to the crank angle sensor because it is now on the other cam bank. I had to use the 1.6 coils and bracket because the 1.8 coil assembly has two electrical connectors instead of the one the 1.6 has. The 1.6 coil bracket was also required because the coil designs are different and the 1.6 coil does not mount in the 1.8 bracket. Since the coil pack is now in a different position not all the spark plug wires are long enough to fit right. I ended up using two number two cylinder wires since the number three wire was too short to reach.

The two flywheels had the same diameter and the same number of teeth, so I was able to use the Centerforce 1.6 unit. If you do use a 1.6 flywheel then the clutch assembly must also be from a 1.6 for they are different designs. One interesting note about the clutch, although the 1.8 clutch has a larger outer diameter (215mm), the inner diameter is also larger, so the total surface area is close to the same as the 1.6 clutch (200mm OD). The OEM 1.8 flywheel weighs 19 pounds verses 18 pounds for the 1.6 unit.

I had to use the 1.6 throttle body because 1.8's air idle control valve's electrical and thermal connections on the throttle body are completely different. Both throttle bodies have the same butterfly diameter of 55mm so I wasn't concerned with choking the motor. The 1.6 throttle body's mounting holes are in different locations so I had to fabricate an adapter plate to mount it to the 1.8 manifold and connect the air idle control passages. That took a whole day in itself!

Since the new motor is 22mm longer than the 1.6, any aftermarket intake system designed for the 1.6 will probably not fit correctly. I had to temporarily revert back to the OEM intake since it is made of flexible rubber and could better take the new contours. Later, I fabricated a custom intake that grabs outside air from behind the headlight.

Obviously, the header is also different because of the larger bore spacing of the 1.8 motor. I wanted to keep my 1.6 Racing Beat header because the oxygen sensor would be in the correct location. It's located in the downpipe the 1.8, while the 1.6 has it in the header tubes, so if you use a 1.8 header and the 1.6 downpipe, you'll have no oxygen sensor fitting unless you add one. I cut the flanges off both headers and had the 1.8 flange welded on the 1.6 header tubes by O'Hare Auto Body in Elk Grove Village, IL.

The early Miata's came with smaller and somewhat weaker rear end assemblies, however they also came with a better 4.30:1 final drive ratio (compared to 4.10:1 for the later cars). I decided to keep the early rear end (equipped with factory viscous limited slip) to get the better ratio even though I will be sacrificing the later cars Torsen LSD (Hopefully a Quaife or Torsen unit for the early rear will one day be available). I theorized that the 4.30:1 combined with the torquier 1.8 should make for a superb holeshot and I was right.

After six months of driving on the street with the new motor and finishing the remainder of the Chicago Region SCCA and Tri-State Sports Car Council (TSSCC) autocross race seasons, I can say this swap was definitely worthwhile. As they say, "There is no replacement for cubic displacement". My Miata is much more of a pleasure to race now, as I no longer feel like I'm dragging a boat anchor.

Prior to the swap, I was starting to get frustrated because I was just barely able to beat the hotshoe C Stock times. Now, I am actually producing legitimate CSP times, and my autocross outlook has been rejuvenated. Overall, my times have dropped by about .5 to .8 seconds for a typical 45-second course.

I haven't had the opportunity to get the car on a chassis dyno yet but my seat-of-pants dyno and autocross times tell me that acceleration is far improved. Informal stopwatch testing shows zero to 60 times of about 7.6 seconds and much greater usable torque output. The car now has enough power to actually light up the rear wheels when exiting a corner and I can now take advantage of the rear wheel drive by getting the back to rotate at will. I also find myself wanting to pull up next to Neon's at stop lights.

Although the new motor runs great, I will probably purchase an aftermarket programmable computer for next season because the 1.6 flowmeter seems to be too restrictive. The motor doesn't seem to pull very hard after about 6500 rpm, although it revs to 8000 rpm with the chip. I'm told that properly set up, an aftermarket programmable computer will add about 10 horsepower to my current setup. However, the problem I have now is that I can't effectively transfer the new found power to the ground, so I might have to settle on getting a better limited slip first.

I would like to thank my wife, Darcy, as she was so understanding and supportive of this project.

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Addendum 5/27/98:

Q: How much HP can I expect from the swap?

A: Peak HP and low RPM torque are two different animals. Aftermarket manufactures sell peak HP numbers, drivability is determined by torque and how much HP is made at the rpm you typically drive in. My 1.6 motor got about 135-140 crank HP and so did my 1.8 using the 1.6 ECU. I gained 0 HP from the swap, the big difference was torque. The 1.8 produces a lot more natural torque from the displacement. Proof is in the 0-60 times. My 1.6 CSP motor got about 8.0 seconds 0-60, the 1.8 w/1.6 ECU (and RX7 flowmeter) got about 7.6.

Update 9/25/98 There are a few ways around having to make an adpater plate for the throttle body. The easiest is to get a programmable ECU. The second is to completely change to the 1.8 electronics. The third is to modify the 1.8 TB so that the TPS functions as a on/off switch just like the 1.6 and then create some type of 'interceptor box' (full of resistor, capacitors and such) to modify the signal to the 1.8 IAC valve.
Update 12/8/08 The easiest way these days is to buy an adapter plate from Flyin' Miata.

Update 12/2/98 I get a lot of inquires about using the Ford Escort GT engine as an alternative as many seem to have found inexpensive examples. The Protege/Escort/Sophia/Tracer 1.8 long block is the same as the 1.8 Miata but all external things are different since they come from a FWD application. Items like the oil pan, thermostat housing pipe, heater core coolant pipe, intake manifold, intake manifold support brace, exhaust manifold, alternator & AC brackets, fuel rail, etc must be sourced from the Miata specific engine. Some items like the Miata valve cover and timing belt cover are optional only if you want the 'Miata' look. Addtionally, some of the 1.6 Miata parts will transfer such as the timing belt cover, cam angle sensor and thermostat housing. IMHO, unless you already have access to the Miata specific stuff it would be easier to just get a Miata motor.

Update 12/30/98 Minor swap tidbits left out of the article. I re-used my 1.6 alternator so I swapped the front crank pulley from the 1.6 to the 1.8 so the V-belt could be retained. This can only be done with a 92/93 pulley since the prior crank snout has a different design. Additionally, I transfered the thermostat housing pipe from the 1.6 to the 1.8, the 1.6 version has the fan temp sensor in it while the 1.8 does not. From memory (3.5+ years ago), the sensors that need to be swapped from the 1.6 to the 1.8 are the oil pressure (real vs idiot), fan temp (and thermostat housing intake pipe too) and flowmeter. The two coolant temp sensors on the back of the motor (one for gauge and one for ECU) I believe are the same but I transferred the 1.6 anyway to be sure. The water to oil cooler, if retained, is plumbed into the TB.

pulley-alt1600.jpg (63 KB)1600 alt. and alt. pulley on 1800
pulleycompare.jpg (44 KB)1600 vs 1800 pulley
thermo1800.jpg (66 KB) 1600 theromostat housing on 1800

The crank pulley designs were changed in late 1991. The later design uses four bolts to hold the pulley onto a crank adapter ring. This design was carried forward though 3/1995 so the late 91-93 1.6 pulley will bolt to the 1.8 adapter ring. If you decide to go with the Unorthodox underdrive pulley you'll get the version that doesn't use the adapter ring. You just simply slip it directly onto the crank. My Unorthodox pulley installation pictures are linked from my Recipe for HP page on the 'street motor' page.

Update 3/20/99 Want to install a '99 motor in an earlier car? The major difference in swapping a '99 vs the 94-97 1.8 is that you'll have to retrofit back in the cam angle sensor or fully change to the '99 ECU and wiring. If you use a '99 ECU you'll also have many wiring obsticles to overcome such as all the gauges are controlled by the '99 ECU while they are not for the earlier cars as well as the '99 wiring harness no provisions to control the headlight motors. If you use a '99 motor with an earlier ECU then you'll have to figure a way to control or deactivating the variable intake runners on the '99 manifold since there is no way to control them without utilizing the 99 ECU. For the VICS control most people just use a rpm activated switch such as the MSD or Summit. I myself used the shift light feature of my Link. Make sure you retain your earlier alternator as the 99+ has no regulator (controlled by the ECU).

Update 3/24/99 Please don't take my 'not for the faint at heart' statement the wrong way. I want to set your expectations that if you have mechanical aptitude and have some experience working on cars then the swap is not hard at all. It is really no more difficult that changing the standard 1.6 engine. It has been three years since I did my swap and we all know a lot more about it now, such as fabricating headers is not required anymore since they now can be bought new ready to go.

Update 6/5/99 If you have a very high idle after you complete the swap the first thing to check for is a vacuum leak somewhere or a mismatched AIC passage. Either of these will let too much air in during idle and cause the idle rpm to be 2000+. Also, when retaining the 1.6 TB for the swap the thermal AIC valve that is on the 1.6 manifold has to be eliminated since there is no provisions for it on the 1.8 manifold (the thermal AIC valve shuts off the air to the AIC when the engine reached operating temperature). Some have installed a selenoid as a replacement. What I did was to install a restrictor in the AIC air intake hose, about 3/32" and re-adjust the air bypass screw in the TB. This allows enough air in during cold start to allow the engine to idle until warm but not enough to cause a super high idle. It is a compromise, the cold idle will be a little low and the hot idle will be a little high (about 1000 rpm).

Update 6/11/99 FYI, If you didn't get motor mount brackets with your new motor then the driver side 1.6 motor mount bracket is similar enough that the hoiles can be elongated and slotted to be reused. The passenger side is different for the 1.8 since it includes a tapped boss for the unique 1.8 starter bracket.


PICTURES (used in article)

1) Engine arrived at Andresen's. Typical junk yard fare.

2) Preparing to remove 1.6. Hood removed and starting to label everything.

3) Note bore spacing differences in exhaust gaskets. 1.8 on top

4) The only wiring change. Lengthened the cam angle sensor wires about 8 inches.

5) Throttle body mounts differed from 1.6 top 1.8. Lower bolts don't even line up let alone air idle control passages.

6) These are the two throttle body gaskets with the prototype of makeshift adapter plate.

Clutchcomp (45 KB)

7) This shows the throttle body mismatch

8) Modification to throttle body to elongate lower left mounting hole. (LR)

9) Modification to intake manifold throttle body mount to 1) notch for throttle position sensor (upper right), 2) mate 1.6 throttle body by drilling new mounting hole (lower right), 3) drill hole to match up air idle control passage (lower middle), 4) shave left side about 1/4" for throttle cable linkage and return spring clearance(upper left).

10) Clutch disc differences. 1.8 on right

Clutchcomp (45 KB)

11) Author Randy Stocker (right) and friend Mark Klauer remove the 1.6 engine.

12) Exhaust header was fabricated using Racing Beat 1.6 tubes with 1.8 OEM flange.

13) Adapter plate was fabricated to mount longer 1.6 throttle cable to 1.8 manifold.