Fitting the K24 Into The RX-8 (Part 2)

completed honda K24 fit into Rx-8

    Continuing from my previous post, my next step was to join the motor and trans together. I actually pushed the motor/trans combo under the car and lifted it up into the car, using some floor jacks and and engine hoist. It was similar to how people drop/put in NC Miata motors. The reason I did this is I didn't have a load leveler, and I was worried about repeatedly bashing the firewall trying to get the trans in.

K24 with clutch

        Putting it together with the adapter kit is pretty straight forward. Just install it like you would on any other clutch. I ended up having to sorta use some different bolts and some washers, etc, because the instructions weren't clear at all. In fact, my kit came with absolutely no instructions at all, so I winged it. That resulted in me doing some sketchy things to get the trans bolted to the plate, and the plate bolted to the motor. If you're using this kit, I would probably call them for instructions.

K24 motor and RX-8 transmission

K24 Custom coolant outlet

    I got the motor all connected together with the trans and the new coolant outlet I got. During this whole test fitting back and forth process, I found out that I needed to actually cut the firewall. The reason being, my coolant outlet was hitting the trans tunnel. When I kept trying to smash and grind it in, I eventually ran into the HVAC unit. So I pulled the motor out for the millionth time and got to work on pulling the dash and removing everything behind it.

RX-8 cut firewall

    I made a JB Weld Special™ firewall plate out of some spare metal that sealed and reformed the firewall so that I had plenty of space to work in. I also added heat tape on both sides in order to seal the heat off a bit from the interior. This ended up being absolutely necessary to fit the K24 head. If you have a K20 head, you wouldn't have to do this at all since the coolant outlet is on the side. I had to remove the HVAC in order to do this, YMMV.

    So here's a checklist of everything I did up to this point:
  • Relocated the ABS module (previous post)
  • Relocated the steering rack (comes with the kit)
  • Cut and sealed the firewall
  • Cut out the center support (you can get away with notching it instead)
  • Flattened the motor mounts (previous post)
  • Cut the subframe and had it welded (previous post)
    After that, the motor's pretty much ready to go. If I'm forgetting something on that list, I'll update this post with it. Also, my next post will include steering column and slave cylinder modifications in order to make that fit.

    Finally, once I tied up all the loose ends, I pulled the motor up into place, installed the motor mounts from the kit, then put the subframe in. A difficult part about installing the motor/trans was getting it to line up with the PPF. I think the kit makes the trans sit slightly more forward, making lining it up a pain. No modifications are required to the PPF as the holes are already elongated to allow for movement, just take your time and slap a nut on the threads as soon as you have enough room to. After all of this, finally, the motor and drivetrain was in. I also got a new valve cover, which I scratched the hell out of during the install. 

rx-8 engine bay with k24

rx-8 with k swap front

rx-8 with honda k swap interior

That's about it for this post. This is the point where I wrapped up the loose ends and pushed the car out into the driveway. If I forgot any more steps on fitting the motor into the car, I'll update this with it. :)


  1. Whats the oil pan situation like? modifications and clearances

    1. You need to cut a section out of the subframe for the oilpan to fit, then have the part you cut out welded for structural support. If you take a look at my part 1 post I have some pictures and info on it as well

    2. do you have any more info on that welding process I am looking at doing it myself?

  2. is there going to be a part 3 about wiring and etc? would love to see it!

    1. Hey, yep :) I have a few outstanding posts I need to make... Currently I haven't tackled the wiring of the swap but I'll be sure to post about it when I do :)

    2. I would love to see the wiring posts
      Im just getting ready to start wiring and not certain if im using both ecus or do adaptronic stand alone


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