Thomas Borchert wrote
The GAMI 'fix' for the problem is really a bandaid solution - instead
of actually fixing the real problem, you measure the extent of it
(with your all-cylinder EGT) and then change the bores of the
injectors until the fuel distribution is off in exactly the same way
as the air distributio

That's not quite what GAMI says, IIRC. They claim the fuel nozzle specs
from TCM and Lyc are so vague that the fuel delivered will vary widely
between cylinders - and that's what's also evened out.

That's disingenuous (on their part, not yours).

It is true that the specs on the fuel nozzles are vague. It is also
true that some of the engines out there are not set up properly with
respect to fuel flow. It is NOT true that this is the major problem.

When setting up an injected engine, there is a classic "coke bottle"
test. Basically, you unscrew the nozzles from the jugs, stick them
into coke bottles, then run the boost pump. After a few minutes, you
have a very good idea of how the fuel distribution is working.
Everyone knows this part of it.

The part that used to be common knowledge, but isn't anymore, is that
(at least with Lycomings) there are different bores of fuel nozzle.
All of them meet spec. By playing with the diameters of the nozzles
(putting smaller ones on the jugs that flow too much and larger ones
on the ones that flow too little) you can very easily make the fuel
flows right - without GAMI's. If you're not too terribly worried
about legalities, you can open up the bores yourself. Like you said -
the specs are so vague, nobody will ever know even if your nozzles are
inspected. In fact, the old style Lyc nozzles were two-part affairs
where the actual nozzle portion was a piece inserted into the bleeder.

If the big issue was fuel rather than air flow, there would not be any
need for test flights and expensive instrumentation. The coke bottle
test would be all you would need. However, that is simply not the
case.

This procedure actually works very well for the baby injected Lycs -
IO-320/360. The air distribution on those is so good that there's no
need to match the fuel flows to the individual jugs, only to each
other. This is why it can be so difficult to lean Lyc O-320/360
engines. We've all met the engine that can be leaned so much that
there is obvious power loss - and it's still running smooth. There is
a tendency to blame the pilot ("you just can't feel the roughness")
but the reality is that some of them have such even air flow (and with
carbureted engines that means the fuel flow is even too, since it's
vapor) that you simply can't feel the onset of roughness.

Such is not the case with the big Continentals. In fact, if you do a
coke bottle test with one of those engines that has GAMI's, you will
see differences in the fuel flows.

Michael