[Diy_efi] injecting 5 port head

[Jean Belanger]

Carter,

The problem with the way you want to do this is that you need injectors that
flow enough fuel at < 25% duty cycle and not 50%. So your idle problem is
even worse that you thought.

You don't really need to have 2 injectors per port. If you only inject when
the intake valves are open then the fuel will be carried to the right
cylinder. This will simplify packaging and injector selection, and help
idle. The scheduling algorithm will then be required to inject for each
injector in a sequence such as pulse, pulse, wait, wait.

In my first version this will even be simplified. You only _need_ to inject
when the intake valve is open for cylinders 1 and 4 (assuming firing order
1342 as for A-series engine). Any fuel injected in the rest of the time will
automatically go to cylinders 2 and 3 when their intake valve opens. So the
injection sequence can then be for both ports: pulse, wait, pulse, wait,
where the first pulse is timed with the open intake valve of cylinder 1 and
the second pulse is timed with cylinder 4. The first pulse of the second
port will inject on closed valves but will go to cylinder 3 when the valve
opens and similarly for the second pulse to cylinder 2. This has the
advantage of not requiring any cam sensor and could even be done with a
single injector driver. Another advantage is that you don't need to worry
about the injector speed because you have plenty of time between pulses for
the injector opening time. Have a look at Marcel Chichak's web site for more
details.

This is not optimal because there will be differences in wall wetting
between cylinders but it should be good enough to get things going and
actually test how much non-optimal this is. A later version will have the
"correct" sequence.

I agree about the variable timing aspect. I'm planning to time the injection
pulse with respect to the middle of the pulse and to have a timing table
that varies timing with respect to RPM and load (either MAP or TPS).

By the way, are you designing your own ECU or are you using an available
one?

Jean

> -----Original Message-----
> From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org] On
> Behalf Of Carter Shore
> Sent: December 26, 2006 10:26 AM
> To: diy_efi at diy-efi.org
> Subject: RE: [Diy_efi] injecting 5 port head
> 
> I face a similar situation with 1147 Spitfire motors,
> siamesed intake ports.
> 
> Here's my plan of attack:
> 
> 1) Use 4 injectors, in sequential order, synchronized
> to crank TDC, and a camshaft sensor.
> 2) Choose injectors that have a narrow spray angle.
> 3) Choose the injector flow such that max fuel
> requirements for a single cylinder requires < 50% duty
> cycle.
> 4) Orient spray away from adjacent cylinder.
> 
> Item 4 means that the injection axes will probably not
> be parallel, which complicates the plumbing somewhat;
> i.e. indiviual fuel hoses to each injector rather than
> a common rail.
> 
> Item 3 means that minimum pulsewidth at idle may be an
> issue, so P&H injectors are probably needed.
> 
> The injection scheduling algorithm may require
> variable timing with respect to RPM and/or throttle
> position to compensate for unequal airflow split.
> 
> Carter Shore
> 
> 
 

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