How many different carburetors were used on the 12a and 13b engines and what are the best aftermarket carbs? Also, what is better between a downdraft or sidedraft setup on these motors?

Thank you

Louwtjie

 

welcome to the board.

you will come to find that asking questions like this, while possibly bringing entertaining answers, it usually isn't very useful or timely. asking what is "best" is purely subjective and if you look at the bottom of the homepage, you will see how many members are registered to this board. each person potentially has a different opinion ... get it?

that said, I am speaking only for 12As and 13Bs in the Rx-7. the 12As only used a Nikki carburetor from the factory. the 13Bs were all fuel injected (though the throttle body was also made by Nikki).

it would be better if you tell us what you are looking to accomplish and ...
1. what characteristics you want with your new setup?
2. how mechanically inclined are you?
3. which of the two engines you have?

down-draughts are pretty versatile and they seem to give you a good balance between low end and high end.

there are two types of side-draughts ...

1. true side-draughts (good luck finding one) are MOSTLY top end.

2. wrap-around side-draughts usually offer good drivability - strong low end and midrange, with lackluster to somewhat decent top end.

keep in mind these are generalizations and you can change jets and venturis to "change" characteristics.

____________

extra information:

the old-school 13Bs used Hitachi carbs, I don't know of them using Nikkis, but there may have been an exception. you're on your own with that research.

I believe the older 12As used both, but I don't know which model car used what.

 

Thank you very much for the welcoming and speedy reply.

I bought a 1985 rx7, and the 12a motor in it is a transplant from an unknown source. I bought it like that. The car starts and runs, but does not idle and runs very poorly. It has a nikki carb on it.

I have two ideas:
1.)Rebuild the 12a motor with a street port and new performance carburetor.
2.)Or buy a 13b turbo japan import motor with ecu and wiring harnas.

I am mechanically inclined, and have 5 years automotive machining experience. I just need to figure out what will be the best for my budget between those two options.

That is my reason for asking about the different carbs. I think both ideas would be fun to build and drive. Just doing my research first.

Also i want to thank everyone involved in this site, this is very very helpful and i love how you can find help everywhere on here.

Louwtjie

 

Rebuild 12a with modded Nikki.

 

unless you specifically WANT a Turbo 13B, i'd say just keep the 12A. get it acting right first before you think about porting though.

 

Carb tech tips:
Rotary Tech Tips: Carburetor Applications

Carb guide:
http://www.racingbeat.com/manuals/intakeguide.pdf

The turbo motor would be a lot of work. The J-spec motors usually need a full rebuild, sometimes even new hard parts, and the crusty old wiring harness and outdated OEM ECU are better replaced by a new standalone EMS and flying lead harness with new sensors. Supporting mods would include an upgraded radiator, high pressure fuel pump, high pressure fuel pressure regulator, new fuel and air filters, associated plumbing, new belts and hoses, full turbo exhaust system, intercooler, and probably some other things that I am forgetting. It would make a great project, especially if you want to show off your mechanic skills, but it would take a fair amount of time and money to get the car on the road.

 

Thank you very much for all the advice.

I bought a book called street rotary by Mark Warner. After reading it, i have a much better understanding of the rotary engine and how all its components work together. With my new knowledge and your advice i have decided to stick with the original motor. I think building a neat normal aspirated 12a will be a great project and i can learn a lot from it before diving in the deep end.

However, i will definitely keep the idea of building a turbo 13b in the back of my head for a future project.

I appreciate your help and once i start my project i will make a engine build thread. Im sure i will still ask a lot of questions.

Louwtjie

 

I have the same dilemma... how much work would rebuilding the engine to allow a street carb cost?

 

welcome to the board. good job on searching.

your question, as asked, is kind of all over the place. first of all, you didn't state what you have. anyway, in terms of work, a rebuild takes time and the amount of time will directly relate to your level of experience and how long it takes to get all necessary parts. the physical act of building will include all cleaning and clearancing, so figure no less than a weekend - in a BEST case (unlikely) scenario. the actual assembly can take a couple hours or more, again, depending on experience/skill.

costs are pointless to discuss at this point because until you have already disassembled it, you won't know what you'll need in addition to basic seals. you can check a few sites for prices on complete rebuild kits (Mazdatrix, Atkins, Pineapple, etc.), but if you end up needed housings and/or rotor(s), then it can raise costs significantly.

i'm not sure what you mean by "... to allow a street carb ...." did you maybe mean street port?