Technical Questions about EFI/ specifically Motec M4

[jmz]

Anyone have first hand knowledge if the Motec M4 in semi-sequential mode is suitable for controlling EFI on our 6 cylider engines?

I don't know much about f.i. or sequenital vs. semi-sequential fuel injection. However, I've been told by a local Porsche shop that the M4 can handle a 911 engine fine. ...not as good perhaps as the m48 but it is considerable less expensive.

I remember reading about CamB's motec controlled 3.2 that had the older Motec box and his engine spit out some impressive numbers so this gives me hope that I can be budget-wise and goe w/ the motec m4 should I choose this route. ...I am still wrestling w/ the 2.8 EFI/MFI or 3.6 motronic for my car.

Below is some info taken from Motec's website


Our M4 ECU is capable of controlling up to 4 High Flow injectors in Sequential Mode. It is the perfect match for a Motorcycle, Honda, Toyota or Mazda 2 Rotor Rotary. Like all of our ECU's it is capable of controlling fuel and ignition on normally aspirated, turbo or supercharged and nitrous oxide assisted engines. In a Semi-Sequential mode, up to 12 cylinders can be controlled using the M4 making it the perfect swap for injected marine engines such as Mercruiser and OMC. This ECU can be enabled to allow data logging and Wide Band Lambda Control

Semi-Sequential Fuel Injection - Semi-Sequential means that 2 or more cylinder's injectors are triggered at the same time, but only 1 time during the engine's cycle. This requires the ECU to be synched with the engine's cycle. Typically injection timing is retarded from the optimum timing point for full sequential by an angle which is equal to 1/2 the angle between 2 cylinders in crankshaft degrees. On a V8 Chevrolet, the injectors for cylinders 1 and 8 would be triggered at the same time. They would be triggered 45 degrees late for cylinder number 1 and 45 degrees early for cylinder number 8. Degrees between 1 and 8 = 90 ; 1/2 of 90 = 45. Semi-sequential allows optimization of injection timing which typically leads to increases in midrange torque and a reduction in fuel consumption for equivalent power compared which Batch fire.

[MotoSook]

Motec=expensive! ... what arm you trying to do with it?

[jmz]

yes expensive, but the M4 is not as expensive as you might think.

As far as my plans, I am trying to formulate them now. I've got a pretty trick 3.0 w/ carbs in the car now, a 2.8 twin-plug motor w/ marelli dual ignition and web 46s in the garage.

I will either put the 2.8 w/ some MFI T.B and stacks controlled by Motec ...not sure about ignition yet. OR sell both engines and convert to 3.6 Motronic.

[Mike Bonkalski]

Sequential is a bit of a misnomer. Essentially, all EFI systems are sequential in that once all cylinders have been injected, the sequence starts from the beginning again. Instead of sequential, think timed injection. This implies that the starting and finishing of the injection pulse is timed with the intake valve opening. The idea behind this is to spray fuel only when airflow in the intake runner is established. This is supposed to mix fuel and air better and reduce manifold wall wetting.

You also talk about batch injection. This is where several injectors are triggered simultaneously and not timed to the intake valve open period. In effect, the fuel sits in the runner for a short period of time before the valve opens and the airflow carries the mixture into the cylinder. The timed concept was developed mainly for tougher emission laws and EPA cycle testing where much of the cycle is run at low rpm and part throttle, where the time available to inject is long and the injector pulse is short.

Performance applications, where your 2.8 RSR w/ ITB's falls, are somewhat different from stock applications. Rpms are generally much higher, fuel flow rates are much higher and emissions usually take a back seat.

As you reach higher rpm's, the amount of time available to inject the fuel decreases. This is true whether the system is timed to valve opening or batch fired. The batch fired system has the advantage of being able to inject fuel for the entire period of crankshaft rotation whereas the timed system technically only has the time available that the air is flowing in the intake runner. This is determined mainly by the camshaft characteristics.

Therefore sequential systems must have larger injectors fitted for a given hp. Remember that there is little airflow and velocity in the port and runner until the valve is open a fairly significant amount. Starting the injection sequence early and finishing late, partially negates the supposed advantages of timed injection.

On a high revving 2.8 RSR engine, there are only a few milliseconds available to inject before the next cycle begins. On the other side of the coin, with batch fired injection, the amount of time that the fuel sits in the port shortens as rpm increases. In the end, there are no significant differences in top end, wide open throttle, horsepower between batch fired and timed systems. Emissions at part throttle are likely to be better with timed injection as this is what it was developed for. But hey, it's a race engine, so who cares.

In a nutshell, don't spend your money on timed injection. Just find a system that will run batch fire and one that you are comfortable with installing and tuning.

[beepbeep]

What Mike said.

Batch vs. sequential is non-issue. Megasquirt, Bosch LH, SDS...they are all batch EFI's , triggering all injectors at once. I've seen dyno pulls with both types and performance delta is minimal. Low-speed emissions suffer slightly in batch-mode but only slightly.

Don't let sequential vs. batch issue guide your choice of EFI...pick one that's cheap, easy to program and fits your needs. If you want hot-cammed MFI-like motor, you might look for something that can do Alpha-N or run in MAP/Alpha-N blended mode as hot cams and individual runners are tough to tune on purely speed-density systems.

[jmz]

I would like something that runs crisp, idles well and screams at w.o.t. Right now my carbs scream at w.o.t. idle OK, but not great, and richen up alot at idle.

sounds like the Motec M4 will do more than enough.

edit for clarity

[Mike Bonkalski]

I would investigate of your options before you decide on Motec. As Beep Beep said, there are a lot of options out there with similar features and different price points.

Be aware that along with the cost of the ECU you can count on a new fuel pump, fuel pressure regulator, fuel lines/fittings, ITB's, fuel rails, injectors, sensors (IAT/CHT), wide-band O2 and a wiring harness. If you can save a few bucks on your ECU that money will definitely go elsewhere.

It should be a cool project. I am looking forward to following your progress.

edit for spelling