The RX8 is a great chassis let down by an engine that is more trouble than it's worth. Don't get me wrong I love rotaries and had a blast driving mine with the stock engine, but longevity, and power are definitely lacking with the Renesis. There's quite a few swaps that've been done, the ones I know of: Mazda (KL, MZ, 20B, 13B) GM (LS, LT, LFX, LF4, 350) Honda (K, J, F) Toyota (JZ, UZ) Nissan (SR, RB, VQ, VH) Mercedes (M113) BMW (S50) Isuzu (6V) Cummins (6BT) Ford (Coyote, 300 I6) Mitsubishi (4G63) VAG (1.8T) and a few electric conversions
LS is the easiest right now since it is the most supported with kits and documentation.
I started my swap back in 2014 and it took me about 2 years to finish, but that's when there weren't that many finished swaps and the knowledge base was limited. Much easier to do them now.
I used the V8Roadsters kit, and I was one of the beta testers for the kit. So refining it was a big part of the time sink, but V8R was really helpful along the way. The beta kit was essentially the NC subframe kit slightly modified, driveshaft and rear end mount kit. I used a GMPP crate LS3 with a GTO T56 and Ford 8.8 I pulled out of a Lincoln Mark VIII and swapped a 31 spline lsd to the use the axles in the kit.
I ended up having to do my own radiator mounting, figure out the wiring and mount for the GM Drive by Wire pedal, air conditioning, and exhaust. Steering rack was swapped from electric to modified hydraulic unit from a NC miata, as it puts the rack in the stock position. Had a bit of a headache with the front sway bar as the early V8R subframe wouldn't work with the stock RX8 bar, it interfered with the crank pulley and ac belt tensioner, and they didn't have a solution yet. I ended up getting a thicker bar made with slightly longer arms and spaced it down 3/8" and used shorter end links, but still had issues with the ac tensioner. Fixed that by using an OEM CTS-V stretch to fit AC belt and ditched the tensioner all together, still had to clearance the ac bracket a bit. They fixed all that in subsequent kits.
To get ABS working you have to use a base model ABS unit. The DSC/ABS unit requires too many inputs from the engine that are no longer present. Base ABS unit is self contained, but needs to have the harness modified to fit the new plug. An ABS module, DSC or base, must be retained as it supplies the speed signal to the dash unless using the V8R CANBUS unit.
The unit needs to be relocated and new lines run to clear the head
To get the dash working there are a couple options.
First option retain the RX8 ECU and harness, fit a crank trigger wheel and sensor and add the coolant and oil pressure switch to the swapped engine. If you use a kit that retains the stock electric rack you'll have to do this anyway.
Second option is run a canbus module. When I started my swap there was only one module available from a guy in England. I ended up getting the last one, as he went out of business about a month after I bought it. Long story short, it didn't work well. It turned off all the dash warning lights, but the tach bounced around like a sugared up 7 year old. I did get the guy who sold it to help me troubleshoot, which involved a round trip of the unit back to England, but the problem persisted. It's a shame as this would have been a great solution for all swaps as it pulled all of it's signals for the dash from standalone sensors so you weren't tied to the CAN protocol of the swap ECU. Fortunately someone on a FB group for RX8 swaps brought his unit to market right when this was going down, and I bought an early unit. Fixed the tach, but had issues with the warning lights, the speedometer would occasionally stop working, and the odometer no longer worked. There was some movement toward a second gen unit, but then he seems to have dropped off the face of the earth. V8R had been working on a unit since before I started my swap, but wasn't ready to deploy it. I finally convinced them to let me test it after all this. After working through some issues with GM's obsession of minor undocumented changes inside ECU families that completely change compatibility of their CAN outputs, the dash works flawlessly. The guy who developed the module for V8R is an awesome guy, and working with him was actually a lot of fun.
From what I can tell the V8R unit is the only one on the market currently. There are a few people that pop up from time to time saying they are developing a unit, but nothing material yet.
This turned out more long winded than I intended, but the short of it is RX8 swaps aren't too difficult as most of complications have been identified and solved. However, don't expect to spend $500 on a blown RX8 and expect to have a running swap for a few thousand more. All the little things that have to be solved add up in time and cost. I went way overkill and over-engineered some things, and spent a lot more for than I could have because I didn't want to cut corners and end up with a janky swap. I wanted a car with as few compromises as possible. Totally worth it to me though, finally has an engine that compliments the chassis. It's a sleeper as I did a very quite exhaust and externally it looks stock other than the wheels. Surprised quite a few people who thought it was just another RX8.
Here's some links to swap companies
V8R https://v8roadsters.com/mazda-rx8-parts-upgrades/ (LS based) can work with most engines if you get a cradle without mounts and make your own
LS1 RX8 https://www.ls1rx8.com/ (LS, JZ, Coyote) uses the stock cradle, can use as a base for other engines
Keisler Automation https://www.keislerautomation.com/ Complete LFX kit
Ronin Speedworks http://www.roninspeedworks.net 8.8 IRS kit
CX Racing https://www.cxracing.com/engine-swap-kit-mazda-rx-8 budget LS 13B