Fitting the K24 Into The RX-8 (Part 1)

    Last post, I finished the backstory about the RX-8 and the K Swap. This is the first post on the actual swap. I received my adapter kit from Collins Performance, and picked up a JDM K24a with the 3-lobe cam. As far as I know, it's the equivalent of a K24a2. The previous owner was saving it as a spare for his sand rail, but ended up going a different route.

    Note: all of the steps I have in this blog are meant to be in addition to the Collins Adapters video linked here on how to fit this into the RX-8 with their swap kit.
RX-8 sitting next to the engine
    The motor came with all of the accessories on it, which I removed. I want to keep the motor as simple as possible, without any extra accessories attached to it. This way, I can get a barebones running swap, and work my way up to all of the 'nice to haves'. That being said, I removed the AC compressor. It looks like there would be room for it, but I didn't want the extra headache of attaching it. 

    As far as the exhaust manifold goes, I kept the stock one that's on there. The reason why is, my plan is to purchase an S2000 manifold and weld the K24 flange onto it. the manifolds almost exactly line up, but the bolt holes are different, hence the K24 flange. On the intake side, one option would be to keep the stock intake manifold and get a RWD plenum. I only saw one for sale, however. Another option would be to get the Skunk2 Intake Manifold, which is suitable for a RWD application. Finally, the last option is to purchase an S2000 manifold, then get this adapter by JSP
K24 on engine stand
    A few things need to be done in order to fit the motor into the car. we'll start with the most important of all; the firewall.

    The firewall is the biggest hurdle in getting this to fit in the car. My advice is, go big or go home. The most ideal option here would be to get a K20 head, because it has the coolant outlet on the side instead of the back. Me, being stubborn, fit mine in with the coolant outlet in the back, which is damn near impossible. I had to do a couple things to make this happen.

    First, the K24 has a coolant temperature sensor in the back, which is the white sensor next to the coolant outlet assembly. I took this off, and will be relocating it to the coolant outlet hose. I put a bolt with an o-ring in its place. Second, and this is an absolute MUST if you're determined to use a K24 head; use a low profile coolant outlet. The stock one will ABSOLUTELY NOT FIT and you NEED to buy an aftermarket one that has the coolant coming out of the side. K-Tuned has one of these you can buy at around $170, or you can buy a generic one on eBay for about $70. Here's a picture of what they look like.
K24 coolant outlet
EDIT: In my next post, I end up having to cut the firewall to make the K24 head fit. YMMV. The info here is slightly outdated.

    The firewall also has to be smashed in. a lot. If you're using a K24 head, it also needs to be heavily grinded. Be careful not to light your car on fire when grinding through the firewall; there's a bunch of padding/insulation right behind it. The part that needs to be grinded is the transmission cowling, because that part has heavy metal which does not bend in. therefore, you need to grind that down in order for the coolant outlet to fit. Finally, regardless of which head you use, you also need to cut and grind the studs that stick out of the firewall for the brake line. 

    I emphasis again, do not be stingy with the hammering and grinding of the firewall. It will make your life so much easier if you do it right the first time. you need to smash in the firewall as far as it goes, then grind the transmission cowl down to the point where it's flush with the smashed in firewall (instead of curving back out), if using a K24 head. 

firewall smashing
reflective heat tape
    This is close to what your firewall should look like after cutting. After I took this picture and tried to test fit the motor, I had to grind down that transmission wall to be flush back with the rest of the firewall. If you're using a K20 head, this won't be an issue.

    This is the hardest part of the physical portion of the swap. Once you have the firewall ready, the rest isn't so bad. The next step is to cut a hole in your subframe. This is because the oil pan has a hump that needs to go into the subframe in order to fit. The Collins Adapters video goes over where to cut, but this is what mine looked like when I was finished.
cut subframe
        When you cut this, make sure to grind down the bottom as flat as you can, so that the oil pan doesn't touch. I ended up grinding that bottom lip down a tad just to be safe. Once you have this cut, you need to get it welded and structurally reinforced. I'll post a picture of mine in the next post, as it's currently being welded at the time of writing this. The adapter kit comes with a steering rack relocation kit to lower the rack a bit, so that the crank pully and oil pan don't touch it. You'll need to get an alignment once your car runs, because relocating the steering rack causes the toe to significantly change. Some people elect to get bump steer kits to help.

        While you have your subframe out, now is a great time to grind down the nubs on your motor mounts. This is because with the kit Collins Adapters has, it goes directly onto these stock RX-8 motor mounts. I did this on both of them.
grinded motor mounts
        Next, you need to relocate your ABS module. Another option would be to completely bypass it. However, you can relocate this further right without any additional materials! All I did was cut off the original mounting point for the unit, then drilled holes in the chassis for the studs on the bracket to go. Finally, when I placed the abs module w/ the bracket into the holes I made, I had access to one of them to secure with a nut.
relocated abs module top
relocated abs module bottom
During all of this, I smashed my knuckles one too many times, so I went to the hardware store to pick up some gloves. At the store, I found a mini RX-8.
baby rx-8
That concludes my part one post for fitting the motor into the car. In the next post, I'll talk about everything else that needs to be done, e.g. grinding the bellhousing to fit the starter, cutting the steering column and modifying that to work, etc. 


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