Good Morning Everyone.

Last summer I had an 85 Base RX7 dropped in my lap by my dad after he decided he didn't want it. I paid him for it and have slowly been tinkering with it. The Carb and vacuum accessories have issues, the interior is dry, and the body has some dents and dings here and there. It could probably use bushings and the rear diff is wet. It's a 12a but most everything is stock except for a coil upgrade. The car itself has 179k miles but it runs great when it is cold, acts like a vacuum leak when it warms up and takes the choke back. I have a carb kit to put into it when the weather breaks.

I'm working on welding a roof onto a 90 miata (MX3 Roof and hatch) and I wanted to put a rotary into that project. I bought an S5 13B engine and transmission off of ebay for it, and it came with all the electronics to run it on a stand and the oil cooler and everything. The engine has 80k miles. I looked into the S5 power specs and it would make the FB quite a lot of fun with that setup, plus I have all the injection components and electronics needed to run it off of a factory ECU. The car's value is very low due to the miles, but it is rust free and fairly complete and original.

Should I put the S5 engine into the FB or should I keep the 12a and just drive it till it gives up and put the s5 setup in the Miata?

Thanks guys!

 

If it were me. I'd run the 12A till it blows up (it'll happen soon with a high mileage engine like that). Then swap in the 13B in the FB and run it carbed. Rebuild the 12A and slide it back in the FB.

With all that done you should have had enough time to route any wires and odds and ins going to the MX5 chassis to make it ready for the 13B fuel injection swap.


In the end I'd have a mostly original ish FB and a fast version of a miata.

 

☝🏽👍🏽 agreed... My 12A has nearly 190k and when it gives up ill rebuild it and put it right back in or I might do it before it goes. Fix the carb/vacuum issue, I'm still running the Nikki carb just a modded one.

 

I have no answers, because I have both a heavily modified FB and one I just bought to keep near stock because being near stock is pleasant in its own way.

I mainly want to see more about sticking an MX3 roof on a Miata. That gets my jimmies rustled in a good way.

I've always thought of the Miata as the real second-generation RX-7 (a nice 1.6l NA is closer to an SA than an FB is!) and it's annoyed me that it was only ever available as a convertible.

 

I think my path will be to get the 12a running properly in the FB and leaving it be (with ignition upgrades). Then the 13B will go into the miata.

I might be crazy for doing the roof and hatch swap, but here is where I am right now. I tooled up to do the sheet metal work, but then the weather went back to freezing cold so I'm on hold again. But the shot bag, shrinker, stretcher, english wheel, and the shears will be flying soon enough.

 

Cooooooooooool.

 

I like.


Gonna go with the factory MX-3 spoiler or the black strip on the back of the hatch?

 

Good idea on keeping the original 12A! Once you get some tings addressed it should run fine as long you're not beating the snot out of it all the time. Basic things like a tune up with NGK BR8EQ-14's, a new cap and rotors, new wires, new belts, replace any brittle vacuum lines, maybe rebuild your carburetor. You may want to make sure the converters are ok. When the engine is running, is there a lot of pressure coming out of the exhaust or is it weak?

An oil and coolant change are in order for sure and I would replace the trans and differential oil as well. If the diff has been seeping then you know its probably low. And remember, we're here to help you get that 12A running properly so feel free to make posts, ask questions, search the forum etc. Any pics of the 85 to share?

 

It has been seeping a little bit out the rear diff. I was considering rebuilding it, but I ran out of good weather. I'm hoping to pretty much daily drive it this summer so it will get the full gambit of fluid changes. The exhaust has leaks somewhere in it, I can hear them. Attached a couple pictures of it.

 

That thing looks incredible!

 

Thanks man, I thought it was a good find. It has it's bumps here and there, and the interior is pretty dry, but overall it is rock solid. I'm hoping another few weeks till I can get it out of storage (Weather still uncooperative).

 

Looks like my mind might have been made up for me last night.

I went to install the new wiper motor and pump the tires up before I brought it home tomorrow out of storage. Fired it up and it just billowed white smoke from up near the exhaust manifold and out the exhaust.

I know on piston engines I would call it a blown headgasket. Would it be the front cover seal on the 12a?

 

I responded in your other thread but no, it may not be that serious. Could just be a leak at the intake
manifold and some coolant seal leaking after sitting. Alumaseal may help the coolant leak if its very
minor.