Plumbing the LFX is a bit backwards from the miata. The LFX is reverse-flow - cold coolant enters the back of the engine, through the thermostat housing & heater core pipes, block, and exits the water pump on the front of the engine to the upper radiator hose. The back of the engine gets pretty busy with a thermostat housing right up against the firewall, along with the lower radiator and heater core hoses. The LFX also uses an expansion tank system vs the miata's recovery tank - the best description of both systems along with their advantages I found was Pirate4x4.Com - The largest off roading and 4x4 website in the world.
. We'll get to that here in a moment.
This is how much space you'll have to work with at the back of the firewall. It's tight. And you have to worry about how the hoses are going to lay on top of each other. After a lot of hmmming and huhing, seeing how the V8 guys do it, and grabbing a 5/8ths tubing bender off ebay, test fitting the a/c evaporator core to see how much room there is between it and the firewall.. we drilled some holes.
If I had to do it over again, I don't know if drilling the outlets staggered top to bottom really made much advantage - but I might stack the holes on the outboard side. Using 45 degree adapters like v8roadsters kit (which wasn't available at the time) would have made coming off the firewall a bit easier as it's a bit recessed and tubenuts / flares like to have a direct shot onto the fitting, and it's very tricky to bend aluminum tubing without a lot of clearance. The firewall isn't very flat except for this area. I swear before I went this route I had seen a 90 degree bulkhead reducing fitting for -10 to -12, but I must have imagined it.
We tried using a HF knockout punch Knockout Punch Kit 10 Pc
for the hole but.. the tool broke. So we ended up using a hole saw. The firewall was a bit thin for the bulkhead fitting so we shimmed it up with 2 washers on both sides. A -12 and -10 AN 90 degree bulkhead fitting and a straight -12 to -10 reducer on the inside (not pictured in this version).
It took a lot of wrangling getting the tube to meet up with the heater box. To make the bend around the back of the heater box we had to trim some of the plastic off. We used a tubing cutter to trim the heater core hardpipe off at the straightest part.
To make a hose barb I found this trick - once again another cheap HF tool - 9-1/2" Wire Crimping Tool
- Cut off the end and grinded it a bit thinner to fit inside the 5/8ths tubing.
The trick with the crimper-as-beader is to go slowly and make multiple passes around the tube. Practice on a piece of scrap first.
If you've installed an M-Tuned reroute, the silicone hose that comes with it is from Vibrant and you can order it in 3 foot sections from summit. It's pretty quality, so we used that to join the heater core up to the tube and gates powergrip thermoplastic clamps. As you'll see, I'm a pretty large fan of these - they give a wide band to compress and don't dig into the hose. With the tubes so close I ended up using a single clamp on both sides.
The stock Camaro heater core tube is.. large and stupid. It exits and shoots up the side of the engine close to where the stock lower radiator hose pipe would go.
Knowing that the LFX engine is used in a lot of transverse mounted engines I figured there might be a chance of finding a heater tube that would shoot straight back - and after a few hours looking through parts catalogs I found the PN 12644554 from a cadillac CTS.
Bingo. One pipe is 5/8ths, the other is 3/4ths (-10 and -12). More vibrant hose and powergrip clamps - and we have something that looks like what V8Roadsters sells.
This corner? It gets busy. Fuel, coolant, A/C, electrical. Vibrant hose is good stuff but some extra protection is good. We split a piece of fuel line tubing and slid it over the edge and a piece of split loom over the hose for chafing.
The stock Camaro pipe goes outside of the exhaust and exits above the alternator, which means you have to shoot it across the engine to the lower radiator hose on the drivers side if you're using anything that resembles a miata radiator. In the NA it'll interfere with the A/C hardpipe and sits above the frame rail. The NB's engine bay is slightly wider and longer and accommodates the pipe a bit easier.
Again I looked at kit bashing from another GM car. Technical drawings are okay for an idea but I found that you can hunt for a PN on ebay or a pulled engine can give you a better idea. This is how I discovered the 2014 CTS pipe - PN 12635783. It hugs the block, goes underneath the exhaust, and exits below the alternator. Originally I accidentally ordered a 2013 CTS pipe which is camaro-like.
Here are the pipes for comparison - from top to bottom - Camaro, 2013 CTS, 2014 CTS.
The CTS pipe fixes the A/C hardline problem - but introduces its own. The stock routing points the pipe right at the swaybar. So, out comes the blue wrench -
We passed the part through the bandsaw a few times, trimming unnecessary wiring loom holders and bits that would make it more difficult to wrestle into place.
We flipped and shortened the bottom pipe bracket so it would meet with the alternator bracket.
Oh - real quick - I should mention this before anyone puts their engine in. YOU WILL NEED TO MODIFY THE ALTERNATOR TOP STUD TO A BOLT.
While we were playing around with the lower radiator hose we removed the alternator - turns out, the top stud is too long to remove with the frame rail in the way. I was able to double nut it out most of the way then trim the excess threads with a cutoff disc and unthreaded it the rest of the way with pliers.
This is the expansion tank in V8Roadsters NB car.
The tank needs to be the highest point in the cooling system. We used some clear vinyl tubing and made a water level to verify our steam port tube (on the top of the tank) was higher than the steam port on the water pump outlet.
We didn't have that much space to put the tank mounted on the firewall. So after looking it for a bit, we moved the tank forward and rotated it 90 degrees by bending some flat stock and reusing threaded bolt holes in the engine bay. We also cut pretty radically into the fusebox tower so we could keep the area just forward of the A/C lines free. The brackets we made were pretty floppy (compared to the firewall) and might shift when filled with coolant, so we put a stand underneath to bear the weight and covered it with high density foam from a yoga mat to prevent chafing.
Here you can see the 3/4in return line we modified in the CTS lower radiator hose.
And here's the tank mounted and the 3/4in Vibrant hose plugged into the return line. Should be able to route the A/C lines around the hose no problem.
The expansion tank is GM PN 22829367 - since its fairly small and short we used the same one. It'll need a 15psi cap PN 15075118 as well. My main complaint with this bottle is the two plastic tabs at the back aren't completely flat, so we had to shim them to fit on our bracketry. The top nipple runs to the water pump outlet (steam port) and is 3/8ths. The bottom is 3/4 and runs into the lower radiator pipe. Once you figure out where your bottle will sit - it's time to modify your pipe.
We snagged Summit Racing PN CTR-20-883 3/8ths steel bung and FSS-84780 3/8ths npt to 3/4 nipple. While the pipe is 1.25in, the tank shouldn't see hardly any flow, and we figured a larger bung would me more cutting and radiusing than necessary. (Originally we ordered a 1/2in NPT bung - we would have had to radius half of it to make it sit flush on the pipe) The bung was welded to the pipe, then we drilled a hole through the pipe and finally attached with plenty of loctite 567 sealant. With the tank and bracketry in place, we could finally see what space we had left over to mount the ECU and ECU fusebox, and cut the 3/4in vibrant hose to size.