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Mazda Rotary Ported Motors
(Mild, Bridge and Peripheral Port)
15th June, 2000
This section is dedicated to the setup of ported Mazda Rotary engines. Whether you run a 10A , 12A , or a 13B , the basic premise is still the same. Once you have your engine ported you are going to have to finish the job with a suitable fuel , intake , exhaust and ignition system. This is where a lot of people get confused and go the wrong way. Rotary engines are quite fragile, and as such require very exacting tuning. Too rich and they will load up , too lean and you will break them. Also you run into many compromises when selecting components. For example , go too large in throttle size and you end up with no drivability , go too small and you don't make any power.  Read on and see what myself and others have done in experimenting with these wonderful engines. I will add to this section as time goes on , so check back every now and then , or email me with some of your own suggestions or criticisms.

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* The engine is RX-7 12A with 13B 6-Port centre plate for in-port injector capabilities
* Haltech E6-A  Fuel / Ignition Engine Management with RA-3 Reluctor Adaptor
* Injection Perfection 2x50mm Weber IDA style throttle body
* 4 x 550cc injectors ex-13B Turbo Series 4
* Fuel rail and Regulator from a 13B 6-Port
* 13B Turbo Crank Trigger
* 3x Haltech Smart Ignitors (Bosche "008" Self Dwell)
* A 13B Turbo Series 5 LEAD Ignition Coil without the OEM ignitor
* 2x Bosche Coils (transformer style) for TRAIL side
* NGK BUR7EQ and BUR9EQ spark plugs. Same as Series 5 & 6  RX-7.

1.   2.   3.   4.

1. Injection Perfection 2x50mm throttle body with four injector locations. Top quality, with ball bearing shaft.
2. Series 5 RX-7 Crank Trigger
3. Individual ignition coil setup with Series 5 Lead coil and Bosche coils used for Trail
4. Fuel Rail and Pressure Regulator from 13B 6-Port with damper removed ( for clearance ).

Now , some EFI rotary basics. If you intend to run big revs , then you will need rather big injectors. This is due to what we call Duty Cycle   i.e   the amount of time the injector can open for.  What happens is that due to your injectors firing once every engine rotation , there is only a certain amount of time available for the injector to open before the next engine rotation. As the revs rise the amount of time that can be used to inject fuel drops because the engine is spinning faster. Eventually you get to a rev where the amount of time the injector needs to stay open to inject all the fuel required is longer than the time it takes for the engine to do one revolution. This is called Full Duty. It means that you cannot put any more fuel into your engine and it is starting to run lean. The way to fix this is to install larger injectors or raise the fuel pressure , either way requiring a total re-map of the injection system.
See the Fuel Injector Sizing Guide from the Setup Tips main page for more details on chosing the correct size for your application.

Next we have the problem you run into with ignition systems on a rotary engine. Running the crank-triggered direct-fire ignition is a great way of doing it. I used to run a Haltech F9-A and an RX-7 distributor. Now running the Direct Fire Ignition ( DFI ) it has not only produced a stronger spark and allowed me to run better spark plugs with a larger gap , but also to fine tune the exact timing required at a particular load and rev , and to also , very importantly , setup Lead / Trail split timing.  This is where the problem lies. the way Mazda has seen fit to run the ignition system is to run a Waste-Spark system for the Lead plugs , and an independant coil for each Trail plug.  What a Waste-Spark system is , is a setup where the one ignition coil, usually a dual-post coil like the 13B Turbo type , fires both plugs at the same time. This causes on espark to fire when it is required in one rotor , and fires another spark into the exhaust cycle of the other rotor , ie. it is wasted. This does not do much for power , but it does help to clean up after the combustion cycle.  The problem : not too many aftermarket EFI computers have the ability to properly setup the Trail ignition side of things. The Haltech E6-A that I am running DOES have these facilities , allowing me to adjust the Trail Split timing via engine load with 32 adjustments , and it has two of these maps  , one for below 2000rpm and one for above. Very nicely done , and quite adjustable. I am pretty sure that Motec and Autronic nowadays have similar adjustments too , but as a Haltech Dealer you know which one I prefer.  To run this sort of system you need a Reluctor Adapter ( RA-3 ) which conditions the signal from the Crank Trigger so that the ECU can use it. Also needed is three igniters. One for the Lead Coil ( dual coil ) , and one each for the Trail Coils. Once setup you have a system as good as Mazda ever intended the Rotary should have.
The newer E6S and E6K systems can run the Mazda crank angle sensor and coil-packs with no accessories needed. Even the Reluctor Adaptor is built in and runs perfect straight out of the box.

This is where we come to the bits you most likely want to know. How to setup the tuning of the engine. Actual values will change with each particular engine and porting technique , but these are the basic settings that my 12A Mild Port runs.

Ignition Timing :
 

Idle	Lead - 6 Degrees BTDC	Trail -  1 Degrees ATDC
Max Load  3500+ rpm	Lead - 32 Degrees BTDC	Trail - 24 Degrees BTDC
Cruise  3500+ rpm	Lead - 39 Degrees BTDC	Trail - 37 Degrees BTDC
Spark Plugs	Lead - NGK BUR7EQ	Trail - NGK BUR9EQ

If you are running a distributor , you cannot go wrong running NGK B9EGV spark plugs.
 

Fuel :  Air / Fuel Ratios
 

Idle	12.7:1
Cruise	13.8:1
Max Load	12.9:1

I will try to get ahold of Weber carby jetting recommendations , and set up a few Weber Tuning tips here soon as well.

Remember , these are the setting I am running , and similar settings on your engine may cause detonation and engine failure. Be very careful when playing with fuel mixtures and especially ignition timing. If you are not sure what you are doing , consult an expert.
I have always used an Autronic MAFM1 to help monitor the mixtures.  Although it is a nice ( albeit expensive ) device to have , I still do not take its reported values as gospel. Instead , I will go mainly by the feel of the engine and use the MAFM1 to help guide me when the engine is running poorly.
 

13B Bridge Port
Doing a 13B Bridgeport or even a Peripheral Port is not really that dissimilar to a mild port engine , other than requiring a little more air flow. Having read the above information on the 12A it should have given you the right idea of how to go about it. The fuel mixtures listed above are almost identical to get optimum power , however , the igntion timing should be retarded more.
When selecting your throttle size , go for a 2x55mm instead of the 50mm throttles , as this will give significant top-end power increases with very little loss in bottom-end response. Going to the trouble of setting up sequential or batch firing is also more critical on these engines as they run a much larger port timing overlap in which the fuel may get blown back up the inlet at lower revs by the exhaust charge , this is known as reversion. The way to go about this is to fire the injectors just before the exhaust port closes. This will help eliminate the reversion.

I have tried experimenting with the 2x55mm throttles. Reversion was happening way too often with this setup , and a longer intake is also required.   Also I think the inlet manifold was not flowing enough for the size of the throttles and further attention should be paid to a free flowing unit.  Basically the inlet system should gradually get larger as it moves away from the port.
We have even played with the Mazda factory racing slide throttles , although not enough time was spent on them to see how well they can work.

Ignition timing on a bridgeport is best left to a constant 20 degrees BTDC for Lead timing and 11 degrees BTDC for trail, as tested at 4500rpm. If you can get to a dyno to experiment you will find very little adjustment from this is needed to get the optimum power.