Ok, this is going to be a wall of text with a few pics, but here's some background on engine selection.
Option 1: GM LFX V6. Just to not get anybody’s hopes up, this isn’t the option I chose. I got this idea from the v8 Roadsters Miata swap kit. And honestly, I got really stuck on this option because it would offer the most power and torque by far and easy to find parts for years to come. But, clearly this is a much bigger project – I thought I could leverage some of V8 roadsters’ products, but there was still a long list of solutions that would have to be developed to get this done. I went down the rabbit hole of what it would take to make this work, and although I didn’t find any actual 100% show stoppers, I could see that this would be a much bigger project.
![](https://s3.us-east-2.amazonaws.com/prod.mm.com/uploads/2021/03/07/1615134618_lfx-side-view_mmthumb.jpg)
![](https://s3.us-east-2.amazonaws.com/prod.mm.com/uploads/2021/03/07/1615134627_lfx-vs-miata-18_mmthumb.jpg)
![](https://s3.us-east-2.amazonaws.com/prod.mm.com/uploads/2021/03/07/1615134655_lfx-bare-block_mmthumb.jpg)
I actually was surprised that I could not find good exterior dimensions for this motor online. I found where someone had posted dimensions from their Colorado, but they were pretty vague and not complete. I tried to use pictures of swapped Miata’s and measurements from my own Miata. I asked v8 Roadsters if they could provide a couple of simple measurements, and they kind of blew me off. I found pics of a bare block, and using the cylinder bore dimension, tried to extrapolate how long and tall the motor was. I even went to Carmax with a tape measure one night and attempted my own measurements on a Camaro (the salesguy was definitely like wtf, but I’m not on commission so whatever). I never really got a clear answer on how tall the motor was above the center of the crank. There may been a major hood scoop required, which doesn’t really work for me. Ultimately, I wasn’t willing to buy a motor for a test fit because I think the overall project is too big, so I moved on to the other 2 options (with only occasional longing for what might have been, lol).
Option 2: Renesis motor. This was actually the most likely candidate when I started thinking about getting this car back on the road. I like this idea because it would match the character of the original motor except would have about double the power to the wheels (with none of that pesky torque to break transmissions and differentials). Plus 9000 rpm! And significantly, I have friends who have swapped Renesis motors into 1st gens for road racing. I could leverage a lot of their efforts and have the car on the road in relatively short order. There are a few downsides though. Namely cost because you cannot use the factory ECU, and I would budget for an engine rebuild because these motors have a terrible reputation (fairly well deserved on the early ones) for reliability/longevity and low mileage used motors are pretty thin on the ground. A quote from one rotary shop owner I talked to “I’ve had four of them and you couldn’t pay me to own another”. But, I honestly think the reliability issue could be mitigated, and realistically, the car is only going to see maybe 1-2k miles per year, so if the motor lasts 50k miles, that’s ok. So I’m not totally scared off by the reliability concern.
I borrowed a core engine from a buddy:
![](https://s3.us-east-2.amazonaws.com/prod.mm.com/uploads/2021/03/07/1615134724_20200727_211345_mmthumb.jpg)
And I have a set of motor mounts they made up, so let's drop it in:
![](https://s3.us-east-2.amazonaws.com/prod.mm.com/uploads/2021/03/07/1615134832_20200815_153121_mmthumb.jpg)
Looks like it was meant to be there:
![](https://s3.us-east-2.amazonaws.com/prod.mm.com/uploads/2021/03/07/1615134898_20200815_154301-2_mmthumb.jpg)
Option 3: 13B Turbo. This was the original plan back in 2006 when I yanked the original motor from the car. I actually bought a jspec motor/trans plus a bunch of other swap parts years ago – it’s been sitting right beside the car for more than a decade. So, this would be the obvious choice, but I am concerned about the supportability of an 80’s turbo rotary from a reliability and parts availability perspective. And I mean reliability as in keeping all the vacuum lines and solenoids and archaic ECU/ignition/sensors happy and finding replacements when needed.
I've been tripping over this for like 15 years, maybe I should put it to use:
![](https://s3.us-east-2.amazonaws.com/prod.mm.com/uploads/2021/03/07/1615135752_20201129_185013_mmthumb.jpg)
TII motor next to the Xmas tree my wife surpised me with for the garage:![](https://s3.us-east-2.amazonaws.com/prod.mm.com/uploads/2021/03/07/1615135827_20201207_221629_mmthumb.jpg)
This could work:
![](https://s3.us-east-2.amazonaws.com/prod.mm.com/uploads/2021/03/07/1615135963_20210115_193916_mmthumb.jpg)
So, deciding which route to go is what I spent waayyy too much time waffling over during the late Summer and Fall.