evilecho

I have a chance to pick up a 13b engine from an 86 RX. Will that engine fit into my '84 RX, it presently has a 12a in it.
Is this possible or is there too much that needs to be retrofitted?
My car has a 12a with manual transmission, the exhaust is shot so I was in the market for a new exhaust. If the exhaust needs rebuilt, it'd be a perfect time to do it. I was looking to put a RB header system on the 12a anyways.

Lastly, should I even bother, or is the 12a better to work with. It needs work, starting to run weak and there is some smoke coming through the exhaust. Smoke could be partly bad exhaust and carb issues.

alien_rx7

Evil,

The swap isn't too difficult. Quite a few people have done it on here and there are plenty of write-pus on how to do it. Just do a search for the swap.

If you're going to do it, you'll need a different RB header since the spacing is slightly different between the 12a and 13b exhaust ports.

If you want to stay with the FI on the '86 engine then you will need the wiring harness and computer plus a new fuel pump too. Otherwise there are a few kits that allow one to swap the FI for a carb instead.

Be aware, the '86 computer had problems with cold solder joints in it and would cause intermittent electrical problems.

hornbm

I'm telling you right now man, forget the EFI. It just isnt worth it. Especially when a carb will make more power.

evilecho

Well, would I be better just building the existing 12a, or would the potential HP with the 13b be worth the swap?

If we keep the 12a, it'll be getting new rb headered exhaust, maybe carb upgrade, and whatever upgrades that are listed in the forums here.

wwilliam54

id put the 13b in , get a carb and a header

hornbm

You can do all that to the 13b too. The only thing you really need to do to bolt in the 13b, is get the modified engine mount from racingbeat and use a 12a or GSL-SE front cover. There is more HP potential in a 13b than a 12a, but the main difference between the two is torque. Rotarys have **** for torque anyway, so you need all you can get.

Some people still perrfer 12a's but the same allways holds true: there is no replacement for displacement in the same type of engine.

The only reason why mazda didnt use the 13b in the first gen from the start is they were still trying to work out the seal problems they had with the 13b's of the 70's.

cosmicbang

There are better EFI systems which will make more power, depending on your budget. Why buy the engine mount? It takes about 30-45 minutes and almost no materials cost to modify the 12a mount.

hornbm

You talking about slotting the 12a mount right? Thats something I would not do. Theres a big risk of a failure from the mounts if you do that. If your gonna spend money on the swap DO IT RIGHT.

As for EFI your talking about aftermarket right? The thing will technically make more power and cost about the same initially. However you forget about tuning it. The aftermarket EFI systems take quite a bit of time and money to tune right.

I'm talking from personaly experience here, not outta my ***. I've tried to go stock efi, thought about going haltech. You know what I went carb. I modified the 12a mount. I wasnt happy with the result. I went and got the racingbeat mount and dont regret it one bit. Its a very well built mount.

cosmicbang

What is the risk of failure and what did you find unsatisfactory about modifying the 12a mount? I'm not exactly sure what you mean by "slotting." The existing opening is already a slot, and what is needed is another slot or hole 20mm to the rear of the original. The 12a mount does not have sufficient excess material for another slot. What I do is first extend it with steel welded on to the ends, and then re-drill the holes (see example). If desired, you could also weld additional steel reinforcement over the last couple inches of the mount ears. When I first did this modification it was 1986 and would have taken over 2 weeks to acquire a mount through international mail. Ever since, it just seemed like the obvious way to go since it was a relatively simple and straightforward solution (and practically free). In 18 years of racing and driving I have been happy with the results and have never had any failure or problems with the modified mounts.

Imho both the stock carb and stock EFI are inferior, and I was referring to aftermarket EFI. Many people seem to have a preference or use whatever they are comfortable with.