Siamesed Intake Runners

[Guest |523|]

I just purchased a V88 to be installed in a 1946 Buick straight-8. It's got siamesed intake runners, that is, eight cylinders but only four runners. Now in the Multipoint Group Fire mode, is it possible to run 4 injectors in sets of 2, firing at 90/270 degree intervals, once per revolution for each group? And is it possible to run 8 injectors staged, 4 primary + 4 secondary, in those intervals?

Before you ask why, read this: It's a 320 cid engine and I'm going to install an ATI Procharger. I'm expecting 450-500 HP @ 15 psi, max power at 5500 rpm, max revs (just in case) at 6000 rpm. Now it gets complicated.

The firing order 1-6-2-5-8-3-7-4 dictates that the cylinders with siamesed ports fire 180/540 degress apart from each other. With a normal batch fire port injection, cylinder #1 steals 75% (540/720) of the fuel (like 6,8 and 3, respectively). So the engine would actually run on four cylinders or burn a hole in piston 2, 5, 7 or 4 (running lean while getting 25% of fuel, 180/720).

Now let's look at the sequential EFI. The stock cam has an intake duration of 265 degrees @ 0.004" lift, meaning the intake valve open times of siamesed ports #1 and #2 overlap by 85 degress (265-180). Which means you can't start squirting to cylinder #2 until #1 intake valve has closed. And then you have 180 degrees to squirt until the #2 valve closes. The valve timing in any pair of siamesed cylinders is always 180 degrees apart, no matter what cam specs. This means a maximum 25% duty cycle (180/720). At 6000 RPM, the engine turns 100 times per second, meaning 0,01 sec/revolution = 10 milliseconds. But we can only squirt 180 degrees = 5 ms. And that's our maximum pulse width at 6000 rpm. In reality, we would start the pulse in advance, before the #1 valve has actually closed, to compensate for the time it takes before the fuel reaches the valve. In addition, when the #1 valve is closing, the #2 valve is already open, and exposed to high piston velocity and suction. Therefore the fuel is likely to be drawn into cylinder #2, even if #1 valve is still slightly open.

But, we can't squirt on cylinder #1 when #7 valve closes. We can't use the 180/540 degree firing order sequence of cylinders 1/2. Because in that case, cylinder #2 would rob some of the fuel intended to cyl #1. What we need to do is make the injector squirt at 360/360 degree intervals, so that cylinder #1 will get roughly half of it's fuel in the port, valve being closed, and half of it when the valve is open. With one injector per port, I calculated I would need approx. 60-70 lb/hr injectors naturally aspirated, and with 15 psi of boost, I'd need around 140 lb/hr injectors, give or take.

What I'm thinking of, is building an intake with two injectors per port; one primary and one secondary, which would step in at boost. I want the engine to idle nicely, as this is a street engine that sees a lot of low speed operation. That's why I think I need two sets of injectors.

I

[rayhall]

This engine is really no different then any other multi group fire engine. The siamese ports with one injector is accommodated in the ECU group fire setup. There is an Injection rate setting that will fire the injectors every 360 degrees rather then 720 degrees.

The injectors are wired like this,

Injector Output 1 = Cylinders 1 and 8

Injector Output 2 = Cylinders 6 and 3

Injector Output 3 = Cylinders 2 and 7

Injector Output 4 = Cylinders 5 and 4

This will mean there are 8 injector events for the engine cycle, and and the injection end angle can be set to the point you require.

If you want staged injection with four more injectors, then select group staged and wire injector outputs 5,6,7,8 like this.

Injector Output 5 = Cylinders 1 and 8

Injector Output 6 = Cylinders 6 and 3

Injector Output 7 = Cylinders 2 and 7

Injector Output 8 = Cylinders 5 and 4

Ray.

[Guest |523|]

Ray, let me try to clear this to myself. Are you saying that in the multi group fire mode, I can make the 4 injectors fire at 90-degree intervals (if chosen to fire twice per cycle) ? That is, four injector events per 360 degrees and 8 events per 720 degrees? And that can be made even in the Group Staged mode?

I'm asking this because the assembly manual claims that in the Group Staged mode, all injector outputs fire simultaneously!

[rayhall]

Yes an injection event every 90 degrees.

I'm asking this because the assembly manual claims that in the Group Staged mode, all injector outputs fire simultaneously!

From the manual.

"This mode allows control of staged injection where the engine uses primary injectors operating all the time and secondary injectors which operate only at higher load/rpm."

This does not mean all four injectors fire at the same time, it just means you cannot go from running on the primary to only just the secondary.

I did how every make a mistake with the group staged wiring. This is needs to be like this..

Primary:

Injector Output 1 = Cylinders 1 and 8

Injector Output 3 = Cylinders 6 and 3

Injector Output 5 = Cylinders 2 and 7

Injector Output 7 = Cylinders 5 and 4

Secondary:

Injector Output 2 = Cylinders 1 and 8

Injector Output 4 = Cylinders 6 and 3

Injector Output 6 = Cylinders 2 and 7

Injector Output 8 = Cylinders 5 and 4

Ray.

[Guest |523|]

Ray, I think the wiring didn't go right the first time, though. With the wiring you described, the injector events for cylinders 1 and 2 (injector #1) would still be 180/540 degrees apart. I made a couple of drawings to illustrate what I think would work correctly. It's the cylinders 2, 5, 7, 4 which need the injection start point to be dead accurate. And that's the closing point of the intake valve of the cylinder that precedes it 180 degrees in the firing order. Cylinder 2 needs the squirt when intake valve 1 closes. Cylinder 5 needs it's dose 90 degrees later, when valve 6 closes. Cylinder 7 needs it's dose 360 degrees later than cylinder 2 (when valve 8 closes), and cylinder 4 needs it's dose 360 degrees later than cylinder 5. Cylinders 1, 6, 8, 3 don't care what is the exact point or squirt, but in this system they will get their share 360 degrees from their siamesed counterpart.[attachment=1]Injector_sequence2.jpg[/attachment][attachment=0]Injector_Output2.jpg[/attachment]

[Guest |523|]

So what I mean is this:

Primary:

Injector Output 1 = Injectors 1 and 4 = Cylinders 2, 7, 1, 8

Injector Output 3 = Injectors 2 and 3 = Cylinders 5, 4, 6, 3

Injector Output 5 = none

Injector Output 7 = none

Secondary:

Injector Output 2 = Injectors 1 and 4

Injector Output 4 = Injectors 2 and 3

Injector Output 6 = none

Injector Output 8 = none

The ECU thinks it's firing 4 injectors in 90 degree intervals, but it's actually firing two injector pairs in 90-270 degree intervals

[Guest |523|]

I'm quoting the Intallation Manual, page 45:

Group Fire Staged Injection

This mode must be used for staged injection if the criteria

required for sequential injection are not met (refer Section 8.15).

In this mode, wire the primary injectors to any of the odd

numbered Injector Drives (Inj1, Inj3, Inj5, Inj7), wire the

secondary injectors to any of the even numbered Injector Drives

(Inj2, Inj4, Inj6, Inj8). In this mode all primary injector drives are

fired at the same time (group fire) and all secondary injector

drives are fired at the same time (group fire). Set the 'Injection

Mode' to 'Group/Staged' when using this configuration.

So this is what got me worried. If it says that "all primary injector drives are fired at the same time", it sounds to me they fire simultaneously rather than at 90 degree intervals.

[Jean Niemi]

(Deleted, reason: I was mis-informed.)

[rayhall]

I have just clarified this with the engineers and all four primary fire at the same time. This means you cannot stage the injectors and will have to use one injector per port and use multi group. This will not be a problem as there are injectors that are 2000cc that will give a perfect idle on engines of only 2L.

Four of these injectors will give you enough fuel for 1200 HP on pump fuel. These are the injectors http://www.injectordynamics.com

[Guest |523|]

Ray, this comes a bit too late.....Tony Palo just shipped me the ID1000 injectors! I chose them because Paul Yaw suggested that I might not be able to get away with the ID2000 injectors (idle and low-speed cruise).

How does the non-staged multi-group mode change things? How should I interpret the following quote from the Installation manual?

In this mode the injectors are fired in two

out-of-phase groups with each group firing once for every 360 or

720 degrees of crankshaft rotation

What does the "out-of-phase" mean? Sounds like a random value not related to firing order.

[rayhall]

Sorry for the confusion..

If you have ordered 8 x 1000 cc injectors then mount two per port, select sequential and wire the injectors this way.

Port 1 Injector 1 = Injector output 1

Port 1 Injector 2 = Injector output 3

Port 2 Injector 1 = Injector output 6

Port 2 Injector 2 = Injector output 8

Port 3 Injector 1 = Injector output 2

Port 3 Injector 2 = Injector output 4

Port 4 Injector 1 = Injector output 5

Port 4 Injector 2 = Injector output 7

Set the firing order in the software to 1-6-2-5-8-3-7-4

This will give you full sequential control on the Siamese ports.

Ray.

[Guest |523|]

I'm getting only 4 injectors from T1. My intention was to choose the secondary injectors based on what the pulse width would be with the primary injectors. Anyway, Jean is going to get a batch of both ID1000 and ID2000 injectors, so I can swap my ID1000 injectors to ID2000. I'm going to run four ID2000 injectors, and double-wire them, so I can get them fire once per revolution in the sequential mode.

In the sequential mode I need to have a sync pulse from the distributor. I need to keep it to drive the oil pump anyway, so I might as well use it for the sync pulse. I currently have the original distributor fitted with a Pertronix Ignitor kit. Could I just drop 7 magnets off and leave 1 magnet there, and use the pertronix module to provide the #1 cylinder reference signal to the ECU?

[rayhall]

The only way to get 8 injector events is to select sequential.

If you want to use just four injectors, then wire them this way,

Port 1 Injector = Injector output 1 and 2

Port 2 Injector = Injector output 3 and 4

Port 3 Injector = Injector output 5 and 6

Port 4 Injector = Injector output 7 and 8

Set the firing order in the software to 1-6-2-5-8-3-7-4

At 50% duty or over the injectors will be fully on.

Yes you will need the sync signal.

Ray.