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GAMI injectors

This is just an update on a post from a while ago.

I have had the TB20 since 2002. GAMIs were fitted in 2003, and I was happy with them. I fly at peak EGT or slightly LOP.

Recently, I was less than happy with the cylinder matching. In particular #3 was running a lot richer than the others and it was quite obvious. It could not have been contamination of the injector orifice because that would make it run lean. So I re-did the GAMI test flight (basically, EGT measurement for all cylinders versus the common fuel flow, and logging the data) and found this

I contacted GAMI and they offered to send me three injectors for #1 #2 and #3, modified to make #1 and #2 peak later and #3 peak earlier, for a very reasonable sum of $99 total. That’s a really good service, after 11 years…

The result is superb

The six black lines are curve-fitted to the EDM700 logged data (6th order polynomial in Excel 2003) and since they clearly all peak together I didn’t bother to number them. As described e.g. here the EDM700 logs the data with a poor resolution of 5F.

The flight performance is immediately improved. At low level (5000ft) settings of 23" 2400 the peak EGT is 11.7 USG/hr. I was previously able to go down to 11.3 before it started to get rough. Normally I fly at 11.5. I can now go down to 10.3 USG/hr which is a huge improvement. You don’t get more MPG when LOP but you get smoother running when the cylinders are well matched.

Note that the reason the data falls off rapidly to the left is because I started the test with the mixture fully rich for about 30 seconds, so I could find the relevant section in the log of the 1 hour flight more easily

As to why the injectors needed changing is a bit of a mystery. I have this data from 2003: before after. To me, it just looks like the data was originally collected with insufficient horizontal (flow rate) precision. However the engine had been rebuilt in 2008 (Lyco SB569 crank swap) and I do know the injectors were returned to the wrong positions then, but that was later rectified.

Last Edited by Peter at 21 Aug 07:24
Administrator
Shoreham EGKA, United Kingdom

Interesting… You must come and fly with me and do the same test and analysis!

The fitting of GAMI injectors and a JPI EDM830 is one of the best things we have done to our PA28-RT.
At 10,000’, at 65% power, using 32" & 2300 rpm, we burn 32 litres an hour.

Rochester, UK, United Kingdom

This analysis is easy to do if you have an engine monitor which logs the data. The test flight is just a few minutes. Obviously you need to get the engine nice and warm and stable and fly in smooth air of fairly constant properties (the EGT and CHT track the OAT, obviously) and on autopilot, but the actual data logging period is just a few mins. I used the watch and every 30 secs leaned the mixture by 0.2 USG/hr.

If you don’t have an engine monitor then you can’t do anything anyway.

Last Edited by Peter at 21 Aug 13:12
Administrator
Shoreham EGKA, United Kingdom

Interesting. Few questions:
Any explanation why injectors would change over time?
What was your GAMI spread before and after?

My GAMI spread sometimes is excellent between 0 and 0.3 gals/hr, other times bad like 1.3 gals/hr. I haven’t found an explanation yet for the variance, except probably inconsistent leaning procedures.

United States

My 1st post has links to before/after.

No idea why injectors might change over time. Very odd…

Administrator
Shoreham EGKA, United Kingdom

I see 0.6 gals/hr spread in the “after” link (and 1 gal/hr before). Do you get this spread consistently, given same conditions, or does it vary?

United States

I haven’t tested it over a range of altitudes etc but would not expect it to vary enough to make a difference.

I would regard a 0.6 USG spread as way too big so I have no idea how that happened. 11 years ago…

The difference yesterday, before/after, is astonishing.

Administrator
Shoreham EGKA, United Kingdom

Peter,
Great to hear that you have finally got your engine to a conforming state!
Now you can explore LOP without loosing to much power in one of your cylinders.

Now you can explore LOP without loosing to much power in one of your cylinders

I have done that before – there is no measurable MPG increase. There is just the 2nd order effect which you get when flying at a low RPM (say 2200) and deeper LOP, but that’s possible only at lower levels (below FL120) because higher up there isn’t enough air for the engine at such low RPM. You get a few % more MPG that way. Now I should be able to do this with a smoother engine.

See the graph in my post here

Last Edited by Peter at 22 Aug 07:12
Administrator
Shoreham EGKA, United Kingdom
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