So you want a 20B 3-rotor in your FC...

So you've heard of the Holy Grail of engine swaps for your FC3S...  Need more info?  Read on...

The 20B-REW engine is the "big block" engine for rotary fans.  The engine was only available from the Japan-only Mazda Eunos Cosmo from 1990 to 1996.  The 20B-REW was an optional engine for the Cosmo, so it made it more rare; estimation on number of Mazda Eunos Cosmos sold with the 20B engine option is numbered under 1,000 units!  All U.S. rotary engines are 2-rotor designs; the 20B is a 3-rotor design, so you can see the obvious 50% increase in displacement is going to increase power potential.  20B's can be bought from most foreign (Japanese) engine importers.
[20B engine - $4,000]

Engine Mounts
Now that you have the 20B in hand, what do you do now?  The hardest part of the engine install is the engine mounts.  If you can fabricate some custom engine mounts, this'll make things a lot easier to bolt in.  Prefabricated Cosmo engines mounts are available from eBay sellers.

The 20B bolts onto the stock FC transmission with no problem.  Remember, the 20B only comes with an automatic transmission option, so it will most likely have a counterweight and flexplate attached to it - you'll need to bolt on an (aftermarket) flywheel to mate up with the FC 5-speed manual transmission.  The automatic transmission counterweight makes it easy to install an aftermarket (lightened) flywheel in this case.  We highly recommend using a Turbo II drivetrain, as non-turbo drivetrains are not as strong as turbo components; the additional torque from the 20B will easily kill non-turbo drivetrain components.  Remember, you NEED the automatic counterweight.  You cannot substitute any of the stock 13B automatic counterweights, so you need a 20B counterweight; an engine without this counterweight is useless.
[Lightened flywheel - $400; ACT Heavy Duty clutch kit - $350]

The 20B comes with twin turbos.  The stock twin-turbo system does fit within the FC engine bay.  Running the stock sequential twin-turbo system is a royal pain unless you're running the stock Cosmo 20B ECU.  It'll be easier to convert the whole sequential system to non-sequential.

A custom downpipe needs to be fabricated to mate with your FC exhaust system.  Else, you can always go with a large single turbo set-up.  We do not know of any pre-fabricated 20B single-turbo manifolds being offered, but one can be welded with a 20B engine flange from Racing Beat (  A (Garrett T04) turbo flange can be bought from most performance turbo shops.
[Custom turbo exhaust manifold, mild steel - $700; turbo - $1,500; oil/water SS AN lines and fittings - $200; intake piping - $100]

A 3-inch exhaust system should be able to handle the exhaust from the 20B for most applications.  If you're shooting for over 500hp, you might want to think about something bigger.  A custom downpipe is in order whether you're going with the stock twin-turbo system or large single set-up.

If you're keeping the stock twin-turbo system, the passenger side intercooler pipe will hit the stock hood.  The stock 20B in a Cosmo uses a front-mounted intercooler, so you'll need to have a front-mounted intercooler installed. 

Oil Cooler Lines
You'll need fabricate at least a new front oil cooler line, since the position of the oil cooler line coming of the front cover is shorter (when using the stock FC oil cooler position).  If you're going to do this project, you might as well and fabricate both oil cooler lines!
[SS -10AN oil cooler lines with AN fittings - $200]

Cooling System
An upgrade radiator is a MUST in this case.  You can also retrofit an FC3S 13BT water pump housing, water pump, and thermostat housing to replace the odd 20B units; it's easier to find replacement belts, since the 20B uses an odd arrangement of both serpentine and v-belts.  The double thermostat design also is a big confusion.  Both upper and lower radiator hoses need to be addressed, as we're talking an additional 10" of engine in front over the original 13BT dimensions.

UPDATE - the FD3S water pump housing and water pump will fit.  The FD3S auxiliary bracket that holds the power steering and AC compressor on the driver's side will fit, but you need to drill some holes to mount the bracket properly; some of the holes already line up!  The FD3S water pump is supposed to flow better than the FC3S unit, so this can be considered an upgrade.  If you run the power steering and AC(?), you need to install all the FD3S pulleys and belts.
[Upgrade radiator - $500; stock FC3S water pump housing, water pump, gaskets - $300]

The stock 20B ignition/coil system used a pair of triple coil groups.  These coils are mounted on the fender are not included with most long-block/engine imports unless you've got a "front-cut".  This would require you to secure at least 6 individual coils (see below).  You'll need to take care of the ignitors, if you're going to fire aftermarket coils.  Some stand-alone EMS units (i.e. Microtech) have built-in ignitors, which can fire an aftermarket coil directly.  Most other stand-alone EMS options don't, so you need to address this problem.  If you're going to run 6 individual coils, you'll need 6 (channels of) ignitiors.  Another option is to go with GM LS-1 coils, as these have built-in ignitors in them; don't rely on these GM coils for high power / high boost applications, as their spark isn't strong enough for big power applications.  If you happen to be lucky to get the stock Cosmo 20B coil packs, MoTeC is one brand that is able to fire them.  Spark plugs wires need to be custom made; mail order places like Summit Racing and Jegs carry custom spark plug kits to cut to you length.  Any local domestic speed shop should be able to help you out with a custom "6-cylinder" spark plug wire set.

Fuel System
The stock FC3S (turbo) fuel pump is not adequate to support a stock 20B engine.  The stock 20B run 6 x 550cc/min fuel injectors, so you're looking at a 50% increase in fuel injector capacity compared to a stock FC3S fuel system.  At the very least, you need an upgrade fuel pump; there are economically priced upgrade fuel pumps under $200 that can easily support 400hp from the 20B.  The Bosch -044 upgrade fuel pump should be enough for 400 to 500hp at the wheels.  If you are shooting for more power, larger fuel injectors and larger (or twin) fuel pump(s) are almost necessary.
[Bosch upgrade fuel pump - $200; SS -6AN lines and fittings - $500; SX FPR - $200; fuel filters - $100]

EFI / Stand-alone ECUs
If you do use the stock ECU, at minimum you're required to use the stock Cosmo 20B coil packs, which are not very easy to find.  On "front cuts", they should be intact, but most imported 20B's do not have them.  The Cosmo 20B coil packs are normally mounted on the fender area, so they are not usually included with just the 20B long block.

In terms of aftermarket ECU options...
There are many options available nowadays.  If you are not going to do the tuning by yourself, please check with what your local shops and tuners are comfortable with:   a crappy aftermarket ECU tuned by a competent tuner will almost always out-perform an expensive ECU tuned badly.

We are comfortable with the Haltech line of aftermarket ECU's.   The top tier Elite series by Haltech offers everything you can want to control a 20B from a street set-up to a full race application.  We also like the Life Racing / Syvecs brand of aftermarket ECU's for those looking to spend a more money.

Additional "Problems"
We've already mentioned the hood clearance problem if you're keeping the stock twin-turbos and intercooler piping.  The front of the upper intake manifold does contact the hood slightly as does part of the power steering pump.

One of the biggest problems of this install is the stock front anti-sway bar.  It will not fit without modification.  This needs to be addressed as we're hanging almost 100 lbs. of "extra" engine weight over the front tires.  You might want to mess around with heavier springs (and shocks?) up front to counter the extra weight - this all comes down to proper suspension tuning for the 20B.

The stock tachometer won't work correctly, but this isn't that big of a problem.  The stock tach can be removed and recalibrated by adjusting a screw on the panel.  By using a calibrated timing device, this can be quickly and easily done.  Input to the stock tach is a negative signal lead, which most coils can output.  Most stand-alone ECU's also can drive the stock tach via a dedicated output.

Bottom line...
With the extra weight up front, it is not as easy as dropping the engine in and having everything work correctly.  Suspension tuning is still a big concern, as not many of these beasts are running around.  Most of them are street vehicles that see very little high performance driving.  Even with it's headaches, once everything the engine is running, the added torque and power potential will make even most cynics crack a little smile...

20B components price breakdown
Component: Price: Comments:
20B engine $4,000 Prices vary, but on average they range between $3,000 - $4,500.
Engine mounts $150 eBay
Flywheel $400 Typical price for lightened steel or aluminum flywheel.  Counterweight should come with engine.
Clutch kit $350 ACT Heavy Duty clutch is only good for ~450lb-ft of torque.  A mildly modded 20B can easily surpass that.
Turbo exhaust manifold {$700} Optional, but if you're going single turbo, you need to have this custom made.
Turbo, T72 {$1,500} Optional - see above.  Price is from Turbonetics.  This turbo is good for 600 to the wheels.
Oil/water lines (for turbo) {$200} Optional - see above.  Includes prices for SS AN lines and fittings for both oil and water lines for turbo CHRA.
Intake pipe (for turbo) {$100} Optional - see above.  Piping and silicone hoses to adapt single turbo to intercooler and for intake going into the turbo itself.
Downpipe $100 Whether you're going single turbo or stock twin turbos, this exhaust pipe is needed to mate with the rest of the exhaust system.
Exhaust system {$800} This might be optional.  If you already have a (larger) aftermarket exhaust system, this might not be necessary.  $500 average for a good "cat back" exhaust, and $300 added for a pre-silencer section to be made.
Front-mount intercooler $1,200 The GReddy R-spec front-mount intercooler kit is the standard for which all front-mount intercoolers are judged for the FC3S.
Oil cooler lines $200 Typical cost to custom fab a pair of oil cooler lines from any name brand SS AN manufacturer (i.e. Earls, Russells, XRP).
Upgrade radiator $500 Cost of an upgrade radiator and custom radiator hoses to fit the 20B inlet/outlets.
FC3S water pump + housing {$300} Optional - if you can get the 20B water pump system, good for you.  If not, we would normally replace the water pump housing and water pump with the stock FC3S units, easily available in the U.S.
GM LS-1 coils {$400} Built-in ignitors
Bosch upgrade fuel pump $300 You can use a pair of Walbro 255lph fuel pumps for a little cheaper.
SS fuel lines and fittings $500 -6AN minimum diameter from gas tank to the engine.  Includes all fittings to convert to parallel fuel rail system with aftermarket FPR.
SX FPR $200 Required to control fuel rail pressure
Fuel filters $100 You'd be crazy to not run fuel filters.  Earls offers a pre-filter and a finer/regular fuel filter at $40/each at Summit Racing.
(Your choice) Starts at $2,000 We recommend Haltech for all our customers.
Front anti-sway bar {$500}  
Just on those estimations, we're looking at a cost of around $10,000 without any of the optional components.
The optional stuff comes out to another $4,500.
Grand total for all components listed would be almost to an even $15,000.
Prices are typical retail, so it's possible to get most of it discounted slightly.

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