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The LE5pard - Nix's Ecotec Miata Build

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where are you with this build?  ii am sad to not see updates.




they just closed on some land and are in the middle of a move I think...

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Primarily, I'm STILL waiting on a wiring harness / ECU. I've been promised delivery next week. I ordered a new one from Swap Specialties, and canceled the order with Alphafab after a few months. Alphafab started to mislead me instead of admitting they were behind on orders. Not OK with that.


Some other things are going on too! I had surgery in December which took me out of the garage and off the track for a few weeks. And as Hollywood notes, we're closing soon on a larger house with enough of a lot (in unrestricted, non HOA area) to build a nice workshop! It won't be a fancy Terry Fair Farm, but a huge improvement. So moving and selling activities are taking priority over race car things.


However I have gotten back in the garage recently to get some work done!



I finished up the fuel line routing and connection. I wanted to make sure to minimize stress on aluminum fittings, so I ran the line to an AN union with gauge that's supported by a bracket, and then a short hose connects via a locking GM fuel rail AN adapter. I'm replacing the brake hard lines with stainless hoses, so they're just pushed out of the way for now. The locking connector for the barbed fitting is the way to go with this, instead of the push on type.








I also finished up the coolant hoses, radiator mounting, and some of the duct work. As planned, I have a steam bomb accumulator tank in the back, which has a connection on the bottom to the thermostat housing below, and the "steam hose" from the high point of the head on the coolant exit runs to the top of it. This should automatically purge any air bubbles that end up in the system.




I welded some brackets to mount the undertray. It's actually split between front and rear undertray, and everything is flush with the lower beam. I use 0.090 aluminum. The front half will pivot upwards like the previous iteration to facilitate trailer loading and potentially help mitigate damage in an off track adventure.



To make sure I'm legal, I mounted up an unmolested OEM bumper and traced out the projection below for the air dam.




I ended up pressure testing the cooling system, and both welds on the thermostat housing are leaking. I had trouble getting the part clean enough and just *sent it* so that's what I get. I'll order a new housing and try again.



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Thanks for the update! Sounds like you have a lot going on! Best wishes on a speedy recovery! Nice to see you back in the garage.

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Moving is a PITA, but sounds like a good workshop would be sweet once setup.


I generally wouldn't worry about strength of the fittings themselves, they're about 10x stronger in bending than the hose ends/any hardlines you might have. Hose has a negative in that it's much heavier than hardline, so forces are magnified on the hose end.


If you want any input on how to support lines/fittings/do brackets, I'd be happy to add some (somewhat?) informed input. It's 90% of my day job (fluid systems stress analyst on a big rocket). 

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I'm STILL waiting on harness / ECU. I should have just built one myself instead of trusting the "professionals" to deliver on time. If you're planning on getting a harness / ECU from Alphafab or Swap Specialties, expect a lead time of 3-4 months (not weeks, even if they say so.)


In the mean time we've moved. We had to flat tow to the new house.




The new place has a lot more space and potential, but is a "fixer upper" for sure. Plenty of room to park the trailer and build a shop.




Unpacking and organizing. I brought over a lot of material. We managed to un-bury the car yesterday.




I received a "shipped" notice from Swap Specialties finally but the tracking number is still in pre-shipment. I haven't counted that chicken as hatched quite yet.

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congrats on the move.  more space is always nice.   unfortunately my vehicular hoarding tendencies are quite gasseous--   the 'collection' expands to fill the space it is provided.  (Currently up to 8 cars, 2 trailers, 5 go karts, and all of the parts that go with them..)

I hope you don't develop the same disease! 🙂

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Not surprisingly, we have been engrossed in massive house projects since moving in. Things have settled down a bit, and I'm working on the car again. Finding all the bits and pieces of car (things like V-band clamps) has been fun post-move. On Saturday I plugged up the harness and ecu, and hotwired the leads to a battery.

It started right up and runs!! Everything seems to be OK so far. I tested the clutch engagement and seems to be working great. Expect a LOT more activity very soon.


The Swap Specialties harness/ECU took forever, but is actually a nice turnkey setup, complete with fuse box. This is definitely the easy button. Connect up power, start motor.


I started on a center console to mount all the wiring, radio, Traqmate, etc. I'm moving the disconnect switch to the center of the car too. Long term plans are to build a defroster setup into this box as well.


I can see a light at the end of the tunnel. The motor runs, car can move under its own power. Build momentum regained.

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4 hours ago, turbogrill said:

Very nice!


Why not use the stock harness?

I wanted to do easy button on this one. There are a bunch of different ECU / harness combos for this engine and I didn't want the headache. Plus most stock harnesses have a body harness connector that has to be dealt with. I'm sure I could have figured out out, but this was much easier.

This also came with a turnkey, pre-tuned ECU and a harness that fit right up with no extraneous connectors.

 Accepting  the long lead time I'd definitely go this route again!

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I had this idea a while back and am going to give it a shot: using Wago lever nuts for connections between the auxiliary stuff (gauge signals, power wiring for accessories.)


We use these for household wiring instead of the traditional wire nut. They're very secure and easy to use. The orange carrier is sold separately for use on DIN rail.


And continued work on the center console and gauges. This is the same gauge panel I used previously, but I remove the section on the left side, where all the toggle switches were. I would hit them with my knee getting in and out of the car. No bueno. I'll mount the toggle switches in the center console, along with the newly relocated master cutoff. 


I built a mount for the ECU in the lower right corner where the AGM battery was. I switched to a larger battery and moved it to the trunk. The fuse/relay box provided with the Swap Specialties harness mounted nicely on the center console.


A lot of TechFlex to install and wiring to do, but it's starting to come together for sure.




The front panel is on a piano hinge, allowing it to swing forward for access to the wiring. The cavity at the bottom is where the radio will mount.


A better view of the ECU and mount plate. It's a GM E67 ECU from a Solstice. 




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Love it! Are you using a bandsaw for the thicker pieces of aluminum plate? Like where that large radius for the ECU mount meets the floor pan?

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2 hours ago, joesurf79 said:

Love it! Are you using a bandsaw for the thicker pieces of aluminum plate? Like where that large radius for the ECU mount meets the floor pan?

I use a band saw where I can and yes I did use one for that cut. It's not always practical since I'm using a small portable saw clamped in a vice. When it won't work I use a jigsaw and tear through blades pretty quickly.

I was cutting tubing with the same saw and had my finger under the work. An ER trip and stitches later, I don't do that anymore.


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😬 yikes! Glad the finger wasnt severed! (by the look of the glove anyway). My hands and usually all cut up, but stitches worthy incidents are pretty rare. And most of the the bad ones have stopped with pressure and superglue Haha! 

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Dude, I totally bandsaw'd a finger about 6 weeks ago and it's still a bit numb/feeling weird. I probably should have gotten stitches, but I just held it together for about 2 weeks with adhesive staples. 


Had a "safety pusher" I was pushing something with, and the part cut through, the saw grabbed the pusher and basically catapulted my finger into the bandsaw. Definitely do not recommend... 


I've been favoring the angle grinder more after that incident... haha

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Bandsaws are amazing... and also very efficient at exposing your stupid when cutting something and putting your meaty bits where they don't belong.

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More electrical work, including gauges and cooling fan. I ran it up to temp last night.

-Oil pressure looks great (whew.)

-Coolant drip from the radiator cap. RTV will fix that.

-Cooling fan comes on, but never shuts off. Probably a tuning issue (shutoff temp below thermostat temp.)

-There's no RPM output wire in the Swap Specialties harness. They responded that "those ECM's don't have a tach output, so you'll need an add-on RPM pickup from the coil signal." However some research shows that on the E67 ECM I should be able to get tach output from J1 pin 25, and J1 pin 24 is a pull up resistor for it. I've ordered some appropriate pins to add to the ECM connector and test it out.

But really, the build is coming together pretty quick, and I'm excited to get it out on track!

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22 minutes ago, edison_GTI said:

If you need an RPM pick up, I have one you can have. 

Thanks, but the fix worked!

On the GM E67 ECM, you can get a tach signal from pin 25 on the J1 (blue) connector. pin 24 is a pull up resistor to make it useful for most tach-driven devices. I ordered some pins (Molex MX64 33467 Series Female Unsealed Terminal 0334670005, Cable Range 20 18 ga (0.50 0.80 mm2)) and added them to the J1 connector, then connected the wires together and to the Traqmate tach input, and it works perfectly. I checked the tune to make sure "crank" type RPM output is enabled - it won't work if the tune is set to serial or frequency engine speed output.



To make room for the pop up headlights, I shortened the radiator hose and ran it through the duct wall. The radiator cap was still leaking despite RTV'ing it - I damaged the mating surface a while back while drilling / tapping the overflow port. I found a 1/2 NPT tap fits the cap neck, so I just tapped it and installed a plug. There's still a pressure relief cap on the expansion tank (steam bomb) so the radiator cap is not needed here.


The garage is already pretty miserable hot, so we pulled the trigger on a mini split!


And I'm still slogging along with the wiring. The center console houses a radio and a cheap Amazon special marine switch panel.





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So I was out on medical for a while, but am back in the garage thrashing away!

Organizing and adding TechFlex split loom tubing to the engine harness. I went this direction over having the harness covered in heat shrink to make modification / troubleshooting easier.


Lighting things up. The switch panel is a pre-made marine/offroad panel from Amazon. It comes with a bunch of little clear decals to label the switches.




Finishing out the trunk. I re-added a full size battery. It's nice to have the extra juice and I need the weight anyway.


All the wiring is cleaned up:


I also decided to rip out all the old brake hard lines. They were 25+ years old, and too close to the exhaust. I opted for pre-made 3AN hose assemblies to replace the lines, and installed a new Wilwood master cylinder.


I routed the rear line through the cabin through a proportioning valve.





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And on to the exterior! I put my "Forged in Fire" skills to the test and made a steel strip that matches the OEM bumper profile. This will be perfect for anchoring the bumper and air dam.


As with the previous iteration, I'm going with a two part air dam with a pivoting bottom section. The top section is anchored to the strip. I had to add washers to get the profile perfect. I went in later and put rivnuts in all of the holes to simplify assembly.


The lower assembly is put together with a zillion rivets. Thank goodness for the Harbor Freight pneumatic rivet gun.


I did some quick and ugly welds on the support frame to keep everything rigid. One of these days I'll sit down with the TIG and learn to weld pretty aluminum beads.


I needed a tow hook, so I repurposed a "baby tooth" that was originally on the car.


Starting to come together


Time to fit the hood and figure out the headlight holes. I purchased a set of pop ups, but the doors won't fill the whole gap created by the venting project:


Solution: make new doors that fit out of aluminum, and attach them to original door mount points with some brackets:



All fit up. Note the bump in the middle of the hood. The Ecotec has VVT oil valves that stick up and the hood was resting on top of them. The bump gives clearance for the oil valves.


All painted up and trimmed:


I still have some duct work to do, to block off the gaps around the radiator and to add brake ducts.


My reward for all the extra complexity and work:


No need to remove anything to load the trailer, and it's more tolerant to off track excursions!

The lower part of the ducts slide alongside the upper ducting:


It's almost ready for on-track shakedown!






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Wow, love this project. I really like what you did with the front dam and ducting. When I did a splitter for the GTI it was always a concern on clearance and ripping stuff up when going off track. I decided to go the 'consumable' route (thanks Lotus) and make the mounting 'sacrificial' (aluminum). Something with a built in escape path is a better idea and more livable.

I am sure it has been asked before...how big of a concern is weight?

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1 minute ago, Just_Hayes said:

Wow, love this project. I really like what you did with the front dam and ducting. When I did a splitter for the GTI it was always a concern on clearance and ripping stuff up when going off track. I decided to go the 'consumable' route (thanks Lotus) and make the mounting 'sacrificial' (aluminum). Something with a built in escape path is a better idea and more livable.

I am sure it has been asked before...how big of a concern is weight?

For this build, I'm shooting for TT5/ST5 - which means I need to gain as much weight as possible! The air dam and undertray assembly weighs less than an OEM Miata bumper though.

I've gone the sacrificial undertray/splitter route before and was effective, but fixing up a new splitter at the track got old pretty quick. With the similar pivoting design it had before, I went off track many times and never sustained damage.

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