I'm currently trapped behind the Great Firewall of China and the company VPN isn't working. MT.net isn't blocked because the People's Republic obviously wants its countrymen to learn how to build fast Miatas instead of just putting sweet decals on boring CUVs and extended wheelbase models of German sedans with the cheapest/smallest engine possible. So why not make a build thread when the rest of the internet isn't accessible?

I bought a severely overheated but otherwise decent NB1 for $750. Was told it "wouldn't start". I towed it home, pulled the terrible looking plugs, and measured 20/0/0/0 psig compression while cranking. The new-ish radiator was full of sludge. Pulled the head and it appeared to have been recently decked. It seems that a shop had attempted to fix this car and it had overheated again. Being the masochist that I am, I decided to fix a compressionless BP4W with an Ecotec swap.



My goal was/is to build a fun street car and not sink a ton of time and money into this thing. I've already got an MZR into NA X-Prepared car (hopefully DP with a future rules change) swap in progress and I didn't want this one to be a boondoggle too. I just want to enjoy my Miata that has a windshield and interior on public roads--a repower and not necessarily an optimized racecar.

I stumbled upon the LEA 2.4L GDI Ecotec and Ecotec Miata's $950 DIY Racer Kit around the same time. I saw Jorge Castillo and Daryk Arden's Church-tuned LEA Miatas laying down ~220 rwhp on Church's high-reading hub dyno and Daryk later netting 208 rwhp/193 ft*lb on World Motorsport's Mustang dyno. Seeing what these guys were able to accomplish with such a simple swap and HP Tuners, I set my benchmark as KMiata's K24A2 with S2000 intake manifold that made 215 Dynojet hp.



So I bought the $950 DIY Racer swap kit, a $550 LEA with 88k miles from a 2012 Equnox, the $250 1320 Performance Slingshot header, gathered the required hardware and other misc. bits, and got to work. Other ecotec build threads are in progress here, so I won’t bore you with generic swap details. It was easy to transfer the ecotec flywheel bolt pattern to my NB flywheel, the Cavalier alternator and starter fit/work fine, and so on. I’ll answer specific questions if you’ve got them.

The main thing I’ve done differently is that I’m running a standalone ECM instead of the normal GM ECM. It’s the same ECM that powers every direct injected inboard ski boat on the market and, no, it’s not for sale to the aftermarket (yet). I made some educated guesses about the engine, actuators, and sensors to create a basemap. For the harness, I bought a used LEA engine harness, chopped the GM header connectors, stripped unneeded wires, and pinned it to my ECM’s header connector. It works great. My car drives much better on the basemap than recent experiences my friends have had with mail order GM ECMs for their DI Ecotecs.



The next thing I’ve done differently is the lower radiator hose and thermostat. Just like jpreston outlined in his build thread, it doesn’t seem completely necessary to plumb coolant almost 360 degrees around the engine. I eliminated the hard pipe that connects the thermostat/bypass/ECT housing to the water pump inlet. I’m instead running a simple L-shaped lower radiator hose that runs under the front ARB to the gap between the dipstick tube, FR edge of engine, and top of oil pan. This routes coolant to a BMW 2002 thermostat, which passes coolant vertically to a hose that connects to the water pump inlet. For the water pump inlet, I made a simple concentric adapter on the lathe—two o-rings and a set screw at the water pump inlet end and hose barb on the other end. No leaks so far. I removed the steel tube beside the ECT sensor and tapped the hole for ½ NPT. A hose connects a barb fitting installed at this location to the bypass port on the thermostat.



Lastly, I’m not sure that it’s terribly unique, but I made my own 3” stainless exhaust with a bigboy MT-approved Magnaflow 22” case muffler. Yes, I had to oval it to get past the clutch slave cylinder and under the transmission. The leading edge of the flex might now be the lowest point of the car. The offset/offset muffler design is nice—it creates a center outlet naturally when the inlet is placed where exhaust wants to pass through the rear subframe. I’ve got about an inch of clearance to the lower subframe brace and to the lower edge of the bumper cover at the front and rear of the muffler. I’m very pleased with the sound level and lack of rasp despite fitting no resonator.



I haven’t made it to the dyno yet, but the car did great at its first autocross right before I left for China. Not bad at all for a cheap car with a cheap engine and a cheap engine swap kit. The engine calibration and intake design are still in flux, so I’ll share more details as they evolve.

 

*like*

 

Awesome, great to see more ecotec Miatas.

 

Can't wait for you to get it on the dyno, Birt!

 

Dyno update!



The blue trace is as-arrived, red is the best run with a 26L x 3OD straight intake tube, and green is with my current 21L x 3OD filtered intake that fits under the hood.



Interesting discovery--the LEA Ecotec has an "advance lock" intake cam phaser. This explains why it wanted absolutely zero intake cam swing before 4200 rpm. I might have lower power than other Ecotecs 4500-6000 rpm due to too much intake cam retard (which I thought was advance at the time). Something to investigate next time I head to the dyno, I guess.



If you're wondering what's up with the ridiculously long intake in the first photo, I iterated pre-throttle intake length and 26" seems about right for best average power with my setup. The back-to-back intake comparison runs were done before further VVT changes were made to pick up some more power and torque. Makes me curious what the long tube would do with the final calibration.



It's still a work in progress. I want to get the air filter down in the LF bumper corner where Andy Hollis put it on his KMiata. E85 will be tried at some point. An LNF high pressure fuel pump will get the HPFP inlet nipple out of the way of cylinder 4 to allow for intake manifold upgrades.

It's fun to drive and I'm excited to get it to the drag strip in this configuration.

 

what standalone ECM is that?