Monday, March 21, 2016

The Ultimate Zoom Zoom: 1992 BMW 325 with Mazda 12A Rotary

The E36 generation BMW 3-series was released in 1990 with "dolphin shape" styling by Darrin Boyer and Joji Nagashima -- but this car isn't known for its styling, it is known as the benchmark for 90s sedan handling.  The Z-axle multilink suspension out back and MacPherson strut with rack-n-pinion up front wasn't tuned to punish you, but offers superb balance in most driving conditions.  Matched with a torquey inline-6 the 325 makes a great canyon carver...but what happens when you swap a rotary Mazda engine?  Find this 1992 BMW 325 with Mazda 12A offered for $4,000 in Cape Coral, FL.

The BMW M50 is a big heavy iron block affair, but somehow the 3-series was able to achieve a decent front-rear weight balance, and folks who swap in alloy V8s report acceptable handling.  However, if you tuck a lightweight rotary far back in the engine bay, you might be able to achieve a rear weight bias that could be even more fun.

Finally, an E36 with a carburetor -- now we're talkin!  The Mazda 12A rotary first appeared in 1970 in the Mazda RX-2 where it made about 130 horsepower, but it was used through 1985 in the RX-7 where it made a few more horsepower.  Thankfully, the 12A is very willing to make more power if you apply some voodoo to the ports and let it breath -- porting a rotary is the equivalent to adding cams/heads to a piston engine, but instead of spending thousands in heads/cams/valves/springs -- you just spend a few hours grinding metal with a die grinder until you make the power you want...but only if you can convince the engine to last while spinning at a billion rpm. My point is that I have no idea how much horsepower this 12A is putting out, but a Holley 700 CFM double pumper can aspirate some serious power.

See a stranger engine swap?


  1. I had a street ported 12a in a chome bumper MGB sucking through a Mikuni side draught. That was a lot of fun. The guy I bought it from reckoned about 165 horsepower. I don't know whether to believe his number, but since it was so light it felt pretty damn quick regardless how much power it had. The carb made all the right induction noises.

    I'm not sure about people who swap a carb'd engine into an injected car. My 12a had a gigantic oil cooler and either too cold a thermostat or too big a radiator. I often had to give it partial choke just to keep it from stalling at red lights. Unless it was driven hard, it wouldn't keep enough heat in the engine to run right, and it preferred to idle above 1000.

    Having owned a rotary swapped not-a-Mazda, I'd gladly own another. I'd even own another with a carb. What I wouldn't do, though, is take a horsepower hit in addition to the unreliability of a carburetor. A BMW M50 is a great engine. To get a 12A up to the same horsepower level involves a bridge-port at minimum, and at that point you really hurt low speed driveability and you won't idle below 1000 at all. Plus the fuel economy will suck, it'll smell like an old carb'd car, and it'll burn oil (by design). This thing is probably a lot of fun on the track, and a bit of a pain on the street.

    1. man this is a big tub o' steel to push around with a little itty bitty rotary like that! wow. me thinks this guy got engine swapping all backwards. maybe if it was a 2002 or 318ti maybe, yeah sure.


  2. DT Correction:
    Boyke Boyer is responsible for the E36 sedan and coupe.
    Joji Nagashima designed the E36/7 otherwise known as the Z3.
    Guess Wikipedia can't be beleived after all.


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