redbarchetta

I have a pristine '88 RX7 FC Convertible with 5-speed MT but the 2nd engine is now shot. Rather than having another expensive rebuild done, I'm going to replace it with an RX8 Renesis 6-port, as several experienced mechanics (including here) advised it's almost like a direct replacement and the most cost efficient option. Not to mention the power upgrade and parts availability problem with 2nd gen rotarys. Assuming I keep my 5-speed trans and not change to the 6-speed, what should be the reasonable approximate labor time / cost for this swap? (avg $130/hr)

WondrousBread

It's impossible to predict the time required for such a swap.

The only real similarities between the Rx8 and Rx7 engine (from a swap perspective) are the relative size and transmission bolt pattern. Mounts are in different places, the electronics are entirely different (you will have to retain the stock Rx8 ECU), there's an immobilizer I think, etc.

That being said, you have the advantage that it has been done recently and need-a-t2, our resident Rx8 engine into FC expert, has written a how-to:

https://www.rx7club.com/other-engine-conversions-non-v-8-118/renesis-13b-msp-into-fc-chassis-how-1158992/.

You can also find lots of good info in his build thread on the same car:

https://www.rx7club.com/build-thread...begin-1155700/

need-a-t2

iTrader: (9)

yeah, as far as engine swaps go, it's pretty straightforward. As Wondrous pointed out, you'll need custom engine mounts especially if you plan on using your stock trans. On that note, I highly suggest you don't. The flywheel on the MSP engine is much larger than the N/A flywheel, and I don't believe you'll be able to bolt on the stock trans without extensive modifications to the trans. For the price, you're better off just getting a 6 speed and an RX7 auto driveshaft like in my build thread. You'll also have a bit more piece of mind knowing the trans wont blow up on you. The NA trans aren’t exactly known for being super robust.

redbarchetta

The shop (Rapscallion Motorsports) is finally ready to start this swap in a couple weeks after being tied up with race season. They haven't done a Renesis-into-FC before, so your detailed reference guide with all the supporting pics, diagrams, charts, will be a valuable roadmap to help work through it without having to figure things out all along the way. I have the ECU and 6-Speed with the engine, so we're going to go with that and get the RX7 auto driveshaft. The "new" ones I've found from various vendors online are in the $300-$400+ range, either Dorman or presumably made by the vendor. The only used ones I've found at the big DFW salvage yard here are manual. I know this can be a mine field so what is your advise for that choice? Great work on this and all the documentation.

need-a-t2

iTrader: (9)

if you have an NA diff, use the auto driveshaft is the path of least resistance. If you have a turbo diff, just start with a turbo driveshaft.

If you really can't find a used driveshaft, for that price i'd likely just have a driveshaft shop custom make you one. I think mazdatrix sells custom shafts for $400, and i'm sure there are cheaper options than that.

thanks, if you guys have questions along the way, don't be shy. I've got around 700 miles on my swap so far and no issues to date.

Also, I hope you got the immobilizer unit from the same car you got the ECU from!

redbarchetta

It's a low mileage, compression verified engine through JDM Dallas that included the wiring harness and ECU. Don't know about the immobilizer unit (bear in mind I'm not a mechanic) but the engine is at the shop and we can verify tomorrow. All of the JDM reps here have advised they haven't had an ECU imported with KCM and Key all included before, and never had a customer bring it up. Am I missing something here because I'm not getting a good vibe about this.

need-a-t2

iTrader: (9)

You may be in luck. I don't think the JDM PCM uses an immobilizer, but don't quote me on that.