Mazda 20B (3 rotor Engine)
Be sure to check out the JC Cosmo, 13G, 20B RX7 and 4 rotor engine pages
at this site. See More
Information below for links.
Several 3 rotor prototype and racing engines have been
produced over the years. Generally speaking these engines were constructed
using the modular nature of the rotary engine (that is to say, the parts
can be "stacked" together).
Generally speaking, the following 3 rotor engines were
"available" from the early 1980s:
20B - Production engine
The 20B engine was only sold in the Japanese market. It
was also only available with twin turbochargers.
This engine appears to use many standard 13B components,
such as rotors /rotor housings, seals etc. As with the "prototype
production 13G" the only obvious custom components are:
NOTE: 20B-REW is the actual correct designation for this
(Picture from 1996/1997 Mazdaspeed catalog Page 104)
This engine is currently (1997) sold by both Mazdaspeed
in Japan and Mazda Motorsports in the USA, both of which are officially
part of Mazda. At first I presumed this was a racing engine based on the
production 20B. However on comparing the photos of the race 20B and the
race 13G, plus the Mazda catalogs list this engine as using rotor housings
with grooves for the water seals, I think it is still a 13G they are selling.
The Complete Mazdaspeed 20B parts list
These pictures have been scanned from the 1996/1997 Mazdaspeed catalogue, Pages 105 to 121 inclusive.
Note: All pictures are 768x1024x4 GIF files. This was found to be the best compromise between file size and picture quality, which is about the same as a fax (to get better quality meant much bigger files).
A second hand production 20B engine is the only multi rotor engine worth considering. The 13G engines are extremely rare (and expensive). The new price of a "20B race engine" as listed above is $US 20,000+ for the core engine alone. Many more 'production' 20B engines were made as they were fitted to a production car rather than being a special racing item. However 20Bs are far rarer than their 13B cousins; so they are difficult to find and will be expensive. (I would estimate that less than 100 of these have been imported to Australia).
In Australia, the price for these units started at $Aus 12000 in
1991, dropping to a low of about $Aus 4000 in 1997. In March 2001 I was told by
someone who had just bought an engine that the going rate is $Aus 4000 to 9000:
So, assuming a 20B can use standard RX7 13B components (rotor housings, seals etc) a rebuild on a 20B could probably be done for under $Aus 3000.
20B engines used in Australia have been fitted to many cars in the Mazda range - RX2, RX3, RX4, RX5, RX7s of all vintages, 929 sedans and Coupes, I have even seen a mid 80's BMW 5 series with a 20B installed. (See elsewhere on this site for both a 2nd Generation RX7 with a 20B conversion and the Rod Millen 20B rally car).
Because the 20B probably has one of the most complex engine management
requirements in the world and the factory computers have complex wiring, these engines generally have the twin turbos
replaced by a single large turbo (eg TO4) and are run on a aftermarket
A standard Mazda transmission will bolt onto the 20B without modification,
another popular choice are 5 speed Toyota Supra gearboxes. Some drag cars are using ancient 2 speed
(why they would use one of these rather than a modern 4 speed is beyond
20Bs have been fitted to later model
RX7s (FC3S/FD3S) without too much problem. (I suspect the RX7 engine bays
MAY have been originally designed to hold a 3 rotor engine, particularly in the FD3S). These conversions seem to retain more of the original hardware.
Rotary engines have been used by many people in the past
as aeroplane engines.
Note with the engine pictures above, the one on the left is a turbocharged 20B, with a propeller speed reduction unit (PSRU) bolted onto the engine where the stock gearbox would normally go. This gearbox allows the propeller speed to be kept under about 2000 RPM, because over this speed the tips of the propeller go supersonic, which creates un-necessary noise and decreases efficiency. (The plywood is part of a test rig, however in the plane this would be the bulkhead).
The one in the middle is a supercharged 20b with a Holley carburettor and a Racing Beat 3 rotor distributor. It was rebuilt and modified by Dave Atkins in Puyallup Washington, USA, for use in an air boat (using an airplane style propeller). The large black pipe in the rear of the picture is an exhaust that has a water cooling sleeve around it, engine cooling water is sucked up out of the lake.
The engine on the right is a Racing Beat's 900hp supercharged 20B (It uses a turbo style compressor driven through step up gearing, on the left of the picture). This engine was anticipated to be fitted to a twin engine plane but I have no further details. I would assume that the basic engine is built to a similar specification as their Bonneville racer.
Note both of the airplanes engines use forced induction for improved power at altitude (aero engines can be non-forced but are generally limited to around 10,000 feet). Carburettors are good for aero applications as they are reliable compared to Fuel injection. When fuel injection is used it is typically a simple mechanical system or occasionally twin electronic units.
These pictures were from the Aircraft Rotary Engine
There is a Company in New Zealand that sells 20B engines for use in aircraft. Here is a copy of his info:
Rotary Engine Power, New Zealand
Thank you for your enquiry about Mazda 20B, 3 rotor, rotary engines. The special features of this engine are its light weight, small size, two spark plugs per rotor, two fuel injectors per rotor, small number of moving parts, runs exceptionally smoothly and is considered to be more reliable than a piston engines Piston engines that are raced are usually reconditioned after every race, rotary engines will last a racing season.
All engines are ex used vehicles with low kilometres. All engines are checked for integrity prior to shipping. Parts availability and supply is not a problem. Most 20B engine components are the same as in twin rotor 13b engines. The basic core of this engine without turbos or fuel injection can produce over 250 hp normally aspirated, with porting 320 hp. As supplied to you, 350 hp with turbos and fuel injectors. This engine if triple turbo charged and ported can produce up to 900 hp but is at present limited by current propeller speed reduction units over 600 hp.
This engine will fit inside most existing fire wall forward dimensions with little modification. This engine installation will normally weigh less than current production lycoming engines of similar horsepower. The total engine installation is around 400 pounds complete. the basic core of the 20B would weigh approx 250 lbs. (There are aluminium housings for this engine that replace the cast iron housings between rotors should weight be a problem, however these are expensive.)
The 20B engine core diameter is 13 inches or 320mm the same diameter as the 13b engine. Length is 26 inches or 666mm. Sump to top of manifolds 28 inches or 700mm. Centre of crank shaft to out side turbo housing 13.5 inches or 340mm. With the turbo chargers the engine would have a width of 320mm, height 700mm and would require little modification. Without the turbo chargers and normally aspirated the engine would have a width of 320mm height 320mm excluding accessories.
This engine can be mounted on its side. 350 hp is approx 6000 rpm, rotor speed 2000 rpm. Piston engine fuel consumption point 4, rotary engines point 5. The rotary weighs less than a piston engine and produces more power, therefore fuel consumption for the same distance is about equal. A tbo of up to 3000 hours could be expected - overhaul is very inexpensive compared to certified engines. We do not supply engine to fire wall mounts.
The p.s.r.u we recommend is a ross aero propeller speed reduction unit. for psrus over 400hp ph fred geschwender 001-402-4383930 usa. We also have a new Barnett 2/1 psru rated at 600hp at around $3000 us.
We can also provide with 20B engines as accessories; propeller speed reduction units, dual ignition distributors, and electronic ignition fuel computers, coils and power packs. The basic engine package does not include ignition, fuel computers, ignition power packs, coils, radiators or heat exchangers. All these components need to be sourced specifically for your fire wall forward requirements.
List of component prices:
Racing Beat and Mazdatrix
can probably help get you the parts you need, but don't waste their time
unless you are serious. The Mazdaspeed/Mazda Motorsports catalogue are the
only place I have ever seen the parts actually listed (with the prices).
This page has everything I know and have been able to find about the 20B engine, so I probably can't answer any specific questions.
Further reading and acknowledgements:
Other relevant reading at Craig's Rotary Page (Please go via the HOME
Other relevant sites on the Internet (Please go via the LINKS
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This page last updated 16/7/2002
16/7/2002 - Added links in more information section and changed references to index page to be called home page.
16/3/2001 - Converted all text to new standard (Headings as Heading1, Some sub-headings (e.g. tables) as 14 point normal bold italic, Most text as Normal, Internal page links at top not all uppercase)
11/3/2001 - Minor content update Engine prices, update to 20B aero engine section. Changed from Netscape to FrontPage and from EWK3.HTM to PG20.HTM (& all sub files). EWK3.HTM changed to redirection page. Background image changed to PG00_02B.JPG
17/11/1997 - Previous known update (May have been some before this)
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