REbuilding the 12A for Vintage Racing
Go to any SCCA road racing event across the country and you will see a lot of 12A motors still pulling hard down the straights.
The 12A motor has been around since 1971 or 1974 for the single dizzy type. With its high revving ear splitting sounds and rock solid reliability as a racing engine, it is easy to see why.
I grew up with RX2 and my favorite RX3’s, the RX3sp, which was just a temporary until the RX7 could get to our shores here in America. What makes it so special? You have to drive one to appreciate one. It is truly a love or hate it scenario at the track. Back when we had megaphones out the back, it was easy to hit 120 db sound limit from a long ways away.
Porting and polishing is the way to get the most out of this little 1146 cc engine. Add in some lightened rotors, competition bearings and the right sized side seals and of course ceramic apex seals and go racing.
We like to do upgrades like add a front port for oiling to the front bearing (vs. waiting for that oil to get all the way through the eccentric shaft to lube it) to keep things slippery. Port out the oil galleys and add in a larger oil pump if you are using the stock front cover.
Another is to add in a larger, fully baffled oil pan to keep more oil and let it get as many bubbles out as possible before the oil pump picks it up and pushes it through our larger than average Setrab competition oil cooler and back into the front and rear bearings at 120 psi. To keep things inside clean under pressure, adding a Peterson inline oil filter means that it is easy to check for bearing wear.
Because it has been years since Mazda Competition made 12A parts, these motors are getting harder and harder to find the old tired 12A automatic engine for parts. Most of the manual tranny cars were driven a lot harder, so I’ve seen customers come in and show me an automatic one and ask if I can build one good motor out of two old engines.
I like to get FD 13B stationary gears and cut them down to 12A size as they are hardened from the factory and help keep rotors in place at high RPM. I’ll also clearance a couple of thousands on the face of the rotors so they don’t get close to the side housings at extended high RPM (it happens).
The 12A is a good motor, low on torque over the bigger 13B, however at the top RPM, it is a screamer.
I have my original 12A bridgeport motor sitting on a cart in the corner, it still runs and got me to the Runoffs every time I put the effort in, and it made a solid 272 hp with a weber carb.