Balancing Injectors vs Air Flow

[Michael F. Sargent]

This is something that just crossed my mind this morning while driving
to work, so feel free to shoot it full of holes....

When an engine is blueprinted (and especially if it is not) the air
flow through the manifolds and heads will not be identical for each
cylinder. Also, injectors will not have exactly the same flow rate.

This means that when you assemble an EFI engine, you can still have a
situation where you have lean cylinders and rich cylinders. This is my
suggestion for balancing these effects.

1) Number the injectors so you can tell them apart. Put injector 1 in cyl 1,
   I2 in C2, etc.

2) Run the engine (preferably on a dyno) at full power, and record the
   exhaust temperature for each exhaust port after things have stabilized.

3) Rotate the injectors, so I1 is now in C2, I2 in C3, etc.

4) Repeat 2) and 3) until all injectors have been tested in all cyls.

5) You'll end up with a table like the following (4 cyl engine):

	Port
	1	Te1i1	Te1i2	Te1i3	Te1i4
	2	Te2i1	Te2i2	Te2i3	Te2i4
	3	Te3i1	Te3i2	Te3i3	Te3i4
	4	Te4i1	Te4i2	Te4i3	Te4i4

   Where TeNiM means the exhaust gas temperature exhaust port N using
   injector M.

6) Add up the exhaust port temperatures for each port for all injectors
   (i.e., sum all Te1i*, Te2i*, ...). This will let you determine which
   is the hotest port.

7) Add up the exhaust port temperatures for all ports for each injector
   (i.e., sum all Te*i1, Te*i2, ...). This will let you know which is
   the hotest (leanest) injector.

8) If any of the values in 6) or 7) is significantly different from the others
   (> 10%???), then you may have another problem worth looking at (bad
   injector or poor flow through one cyl) that should be dealt with first.

9) If all are not too far off, then pair the hottest injector with the
   coolest port, etc. down to the coolest injector with the hottest port.

10) A final dyno run should show exhaust gas temperatures that are fairly
    uniform, indicating that each cylinder is doing almost the same
    amount of work.

11) Finally, in a DIY_EFI controller, a small amount of per injector
    correction could be added to completely balance the engine.

Well how does this sound? Am I completely out to lunch? Or is this to small
of an adjustment to be worthwhile?
                                      Mike
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| Michael F. Sargent   | Net: msargent at gallium.com | Phone: 1(613)721-0902 |
| Gallium Software Inc.|                           | FAX:   1(613)721-1278 |
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