KMiata Swap – Cooling

Thankfully for the most part, the cooling situation on these if fairly straight forward and a known quantity, though there’s *always* some custom work to be done.

First thing’s first, the hoses. The upper hose can be made from a Dayco 72277 and a Dayco 72098, with a 12″ coupler between them, and the lower is a Dayco 71718. They’ll all be need to be lightly trimmed to fit, but they’ll get you most of the way there.

Of course, a 12″ coupler doesn’t seem to exist off the shelf, so I bought some aluminum tubing and a bead roller and got to work:

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I made a strap out of a piece of tubing to secure the front of the upper radiator hose away from the front corner of the block, and the accessory belt idler pulley:

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I’d been using a stock radiator for mock up so as to not risk dinging up the nice aluminum rad, but quickly found a clearance problem with the stock fan bolted on the thicker core aluminum rad, as it did not fit between the radiator and front sway bar.

With a slim-line fan ordered, I could get busy building mounts. I used the “through the core zip-tie” style ‘mounts’ it came with to secure it in place and give me something to aim at:

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I cut the mounts out of steel plate. Aluminum *might* be strong enough for this (especially some CNC’d billet mounts), but this is critical enough that I’ll take the weight penalty for over-building it. I did turn up a set of spacers on the lathe out of aluminum, and the fan is bolting through weld nuts on the bottom of the mount plates

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With the critical features of the lower mount done, the simpler top mount could be made:

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A quick test fit shows PLENTY of room to the front sway bar:

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Once all the critical fitup was done, less critical Speed Holes can be drilled:

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A lick of paint and some foam-rubber insulation to seal the fan to the core, and prevent chafing:

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Mint!

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KMiata Swap – Engine Prep

There it is, the star of the show! The Honda K24a2 from an 06-08 Acura TSX.

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The first task was to strip everything unnecessary off of it. All new wiring is going in, but I’ll likely need some connectors off of the old harness, so everything gets labeled.

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A few mods need to be made for the K-series to fit the Miata. The biggest of those is the oil pump. The a2 variant has a massive pump assembly with counter-balance shafts sitting right where the steering rack wants to live. That’s replaced with a much slimmer pump from a K20, along with a back-cover, pickup and windage tray to work specifically with the KMiata swap.

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The timing cover, chains, guides and tensioners all need to come out to get at the pump. While it was already apart (and since it was 1 extra bolt to replace it), a 50-degree variable intake cam pulley from the RSX Type-S took the place of the 25-degree sweep unit from the TSX.

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Leak testing the pan before it goes on.

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A new gasket & seals set from Honda went in to replace anything worn. The O-rings around the oil system and for the VTEC solenoids were notable in being seriously perished.

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That done, the front of the engine could go back together. Timing chain, guides, tensioner, timing cover, water pump and housing:

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Because I’m using the ATI damper, which is smaller than the stock harmonic balancer, I ended up needing to go with a shorter belt (a 6PK1035, if anyone reading this decides they need to go in a similar direction):

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I love the simplicity of KMiata’s 4-pulley setup, but I’m not really happy with the tensioning setup. As this post is long enough, I’ll dedicate a separate post to that adventure. I’ve no doubt that it works, but I can’t help but picture myself trying to fix an alternator or water pump in a wet / dirt . gravel / grass paddock space at a track or on the side of a mountain, and losing half of those parts in the dirt.

You’ll notice at some point here the engine was installed. That was a HUGE morale booster. There wasn’t much super interesting with that, it slid right in, however I do want to share a tip that’s been passed down to me from others that I found super useful: Making dowels to line up the transmission and engine.

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That made getting the transmission on SO much easier.

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Another quirk of the KMiata swap is that the starter is on the “wrong” side of the engine relative to the Miata’s, so the transmission bellhousing needs to be clearanced for it to fit:

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Next up was to start making and test-fitting cooling system parts. The lower radiator hose (a stock S2000 lower hose) was fairly straight forward:

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The upper hose seems to need to be 3 pieces. I’m still on the hunt for a single hose solution, but for now, it looks like a 72277 and a 72098 hose with a long coupler need to be used.

A 1 foot length of aluminum tube seemed to be just about perfect. A couple of passes run on the bead-roller made a nice looking piece:

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I’m going to put some more anti-abrasion sleeve and a bit of retention where it wraps around the front of the engine, because while it doesn’t touch while not loaded, I imagine when it’s full of water and moving with the car & engine, it’ll definitely rub there. Worst case it’s easy / cheap insurance that I’m not wetting down the course / track.

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Yes that’s a stock radiator. No, it won’t be in the final setup. I’m using it for mockup now to avoid dinging up the shiny aluminum one while still building this setup.

On to the other side of the motor, I can mock up the exhaust manifold. It is on the ‘wrong’ side of the engine (compared to the stock Miata configuration), so it has a crossover tube that bolts on that runs between the bell housing and oil pan.

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Unfortunately here I run into another V8Roadsters subframe issue. The crossover pipe runs into the hoop that connects both sides of the subframe and runs under the engine.

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So now I have the pleasure of taking a freshly ceramic coated to the grinder to gain a couple millimeters of clearance. Which is nice…

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So now it clears, but…ugh.

At least it won’t affect performance, or rattle every time I come off throttle.

Next up, the fuel and accessory belt systems.