just wondering what the pros and cons of each are?

A little more information about your project might get you some more helpful information, but stated simply, the 13B rotors are wider, hence more displacement, hence more power and torque. And, since no Mazda with a 12A has been sold in this country since 1985, parts for are getting harder to find.

ok well i have a 1980 series 1 rx7 with a stock naturally aspirated 12a engine. im after between 150bhp to 200bhp from a naturally aspirated set up and unfortunately im on a budget. what would be better for me in this project, modifying the existing 12a or having it swapped out for a 13b? any help is greatly appreciated as always

the 12A stock can flow enough air to do about 150hp at the FLYWHEEL. the 13B depends, as they have made many different ones over the years, for instance an rx8 engine does about 180hp to the wheels stock.

ok so if thats 150bhp at the flywheel, how much of that gets to the wheels in stock form? how you can improve the amount of power which gets put to the wheels from the flywheel? sorry, im a complete rotary and mechanical noob. im keen to learn though =)

it might do 130-135 at the wheels, you have the spin the flywheel, transmission, driveshaft, rear end, and tires.



big difference between the 12A and 13B is that the 13B is a little bigger, and its been developed more, depending on which one you pick. cost to build a 12a vs 13b is basically the same

If I were having to build a motor and had the choice I wouldn't even give the 12a a minutes thought.

ok, yeah its just the initial conversion cost thats gana be a pain to go from a 12a to a 13b. so thats what youd all recommend? switch to a 13b and build that up?

unless you get a good deal on something else, yeah.

ok thanks for the help. ive had a look around and i can a 13bREW twin turbo fitted in a couple of months whilst i get the cash together. what starting mods would you recommend on that platform? im thinking of doing the lighter stuff to begin with, spark plugs & leads, air & oil filters. would the stock tranny from my 12a be able to handle the new engine? the only mod to the tranny is a heavy duty clutch