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Fitting a 20B engine to an FC3S RX7 (2nd Generation 1986-1991).

Transmission and engine mounts / Other engine mounting issues / Turbos, fuel system and exhaust / Engine management / Mazda's prototype 3 rotor RX7 / More information


This car is a 1987 FC3S RX7 TurboII (Second Generation RX7), It's owner is Chito in Los Angeles, California, USA.
The car was originally left hand drive (as are most cars in the US, except postal delivery vans) but was converted to right hand drive using parts from a wrecked Japanese import. The engine that has been fitted is a 20B engine from the Eunos Cosmo. (There are pages about both the 20B and the Cosmo elsewhere on this site).

Rear view
(384 x 303)

Side View
(510 x 288)

Front View

20B turbo engine

20B turbo engine

20B turbo engine

2 x TEC 1 Ignition

Main EFI computer

Main EFI computer

Transmission and engine mounts:

The original 13B TurboII transmission was used, with the original transmission cross member bolted at all the same original places.
The 20B flywheel was replaced with the original TurboII flywheel although using the 20B counterweight.
The original TurboII starter motor was also used.

In order to fabricate engine mounts, the transmission was bolted to the engine and to the body, thereby leaving the engine unmounted at the front.
The 20B engine mounts are located to the rear of the engine (on the cast iron housing between the rear two rotors).
The original engine cross member is used in a modified form, cut and welded towards the back of the cross member to accommodate the original 20B engine mounts.
The standard RX7 TurboII drive shaft and differential are used.

Other engine mounting issues:

As the 20B is about 7 inches longer than the 13B TurboII engine, the original radiator was replaced with an aluminium one located further forward (and necessitates using some big electric fans).
In this case, with the large intercooler, there was significant modification towards the nose of the car to accommodate it.
Furthermore due to a lack of room the Air Conditioner cannot be used and the front sway bar need to be adapted because the 20B engine will hit the sway bar.

Turbos, fuel system and exhaust:

Due to the complex layout of the 20B's original sequential turbos, these were removed and replaced with a single large turbo.
The original 20B in the Eunos Cosmo generates a stock 280hp, up to around 350-400 with minor modifications.
With the T-64 turbonetics single turbo, the target is at least 500hp.

550cc injectors have been used on the primaries and 1200cc injectors on the secondaries. Given that, the engine should be capable of 10 - 12 lbs boost with a little left over in injector capacity so it does not lean out.

The exhaust is custom made, with a 3.5 inch downpipe to a 3.5 inch Borla stainless steel resonator branching into two 3 inch pipes and two 3 inch exhaust, all made from stainless steel. Evidently it sounds great!

Engine Management:

Two electromotive TEC1 engine management systems are used, with two sets of three coils each, one spark plug per coil (the other side of the coil is grounded).
(3 rotors x 2 plugs = 6 plugs, 1 coil per plug)

Two crank angle sensors are used, which are 180 degrees apart, one for leading and the other side, trailing. These sensors were installed inside the original 20B crank angle sensor. (The 20B crank angle sensor is located at the same place where the 13B distributor is).

The TEC units manage the ignition timing as well as fuel injection, with the main computers mounted in the polished aluminium compartment and the coil packs mounted on the suspension tower (TEC II units combine the computer and coil pack into one unit).

Mazda's Prototype 3 rotor 2nd generation RX7:

Mazda's early multi rotor engines had problems due to the design of the eccentric shaft. When this was overcome in the mid 1980s, Mazda started to build them mainly for racing. However the engineers tried several modified production cars with these engines.
Firstly a 1st generation RX-7, then in 1988 (the RX-7's 10th anniversary) a 2nd generation RX7.
This car was taken to the USA (Mazda's biggest market), for a number of automotive writers to evaluate. This caused speculation that a multi-rotor RX-7 may well be produced.

The car pictured below was fitted with a naturally aspirated 3 rotor engine, which probably would have been a 13G 3 rotor engine (Note that the 13G was never used in any production cars, however the related 20B was).

As the 13B 2 rotor fitted to the RX7 of the day was 654cc x 2 rotors = 1308cc, 146bhp@6500rpm , 187Nm(138lbft)@3500, one would speculate that the 13G with 654cc x 3 rotors would make 220bhp/280Nm(207lbft) at the same RPM, however this is only an estimate.

3 rotor RX7
(640 x 480)

13G (?) engine
(640 x 480)

More Information:

Thanks to Chito for the pictures and information about his conversion. His email address was however I have since tried to contact him on several occasions without success.

Further reading and acknowledgements:
* Books (RX7 by J. Yamaguchi, 2nd edition - Factory 3 rotor RX7)

Other relevant reading at Craig's Rotary Page (Please go via the INDEX page):
* 20B Engine (The engine used in this RX7)
* My 1994 USA trip (Rod Millen's 20B RX7)
* Books (RX7 by J. Yamaguchi)
* 13G engine (The engine used in the Factory RX7)

Other relevant sites on the Internet (Please go via the LINKS page):
* There is an extensive page about this swap at FC3S PRO
* Team FC3S (Extensive collection of information related to this model RX7)
* Search for Chito

This page last updated 19/8/2005
Update History:
19/8/2005 - Added FC3S PRO link
26/3/2001 - Renamed from PG02.HTM to PG25.HTM and all images to PG25_XXY.ZZZ to make room for site admin pages
17/3/2001 - Changes to More Information section
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 (Spelling mistakes, tidy up). 'More information' section in new format. Changed from Netscape to FrontPage. Background image changed to PG00_02B.JPG
10/9/1997 - Previous known update (May have been some before this)

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