Clubuser

I'm in the process of converting to Microsquirt from stock on my TII. As you all know, no sequential spitting.

So, I was thinking if the secondaries where to take the role of the primaries, how would it affect performance. Would it be closer to sequential in terms of better drivability, better fuel economy, lower emissions?

Bet no one has given this a thought before. LOL

scotty305

iTrader: (2)

I'm not completely sure what you're asking, so here's some info that I hope will be useful. 'Batch fire' usually means to fire the injectors twice as often as they need to fire, and 'sequential' usually means firing the injectors only as often as the intake port is open. On a rotary engine the intake port opens once per 360 degrees, so firing the injectors once per 360 degrees is considered sequential for a rotary engine (also for a 2-stroke piston engine, their intake reed valves open once per 360 degrees). Firing an injector every 360 degrees might be called batch-fire on a 4-storke piston engine, for those guys sequential injection means the injectors fire once per 720 degrees to match their intake valve opening.

Rotary engines also use staged throttle bodies and staged injection, very similar to how some carburetors have primary and secondary blades. The primary throttle and primary injectors on our rotary engines are active at idle and cruise, and the secondary throttle and secondary injectors are active above about 30% as measured by the throttle position sensor. I know of someone who swapped the OEM throttle for a big single throttle blade and is now running all four injectors all the time on a 13BREW, it looks to be working well even at idle and cruise.


Personally I would try to avoid firing the injectors every 180 degrees, because rotary engines don't have valves. Spraying fuel when the intake port is 'closed' (actually shrouded by the rotor) will spray fuel onto the side of the rotor and may contaminate the oil.

Clubuser

I just have this crazy thought that with batch firing, with the secondary acting as the primary might result in better low load drivability.

Hadn't thought about with batch firing, fuel rams onto the rotor's side. But same can be said when carbureted. Another reason to supplement the fuel with 2 stroke oil.

scotty305

iTrader: (2)

If you still have the factory throttle body, there won't be any air flowing through the secondary intake runners at idle or low load. Remove the intake piping (and intercooler if you still have the stock top-mount) and watch the throttle blades while someone presses the gas pedal. At light load, the secondary throttle blades are shut.

Without air to carry it along, the fuel sprayed from the secondary injectors when the secondary throttle blades are shut would just dribble on the intake runner walls instead of mixing with air to get inside the combustion chamber. The fuel won't burn well or make good power if it's not mixed with the air well. Imagine a cigarette lighter igniting a nice fine mist of hair spray from an aerosol can, vs the same lighter igniting a puddle of the same hair spray that's been sprayed and allowed to pool in a bowl or on the ground.

Unless you've changed your throttle body or adjusted the linkages to open the secondaries earlier, I think that primary injectors for idle and light load will have the best behavior. It wouldn't have cost Mazda anything to program the secondary injectors to run at idle, and it would have been cheaper to use a single-blade throttle. So we have to assume they had reasons for the way they did it.