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"zero" GAMI spread thanks to Don at AFP

scsmith

scsmith

Well Known Member
I've been flying with an IO-360-A1A straight out of the box, running LOP with a GAMI spread of about 0.3 gph. It has been fine, but looking at my data, I wondered if I could do better. Three of the four cylinders peak at essentially the same time, and one cylinder just lagged a bit. The upshot of that is by the time I get that one cylinder 30F or so LOP, the other three are more like 70F LOP.

So, I got to thinking, if I could just get a very slightly smaller injector nozzle for that one cylinder, they might all peak together.

After speaking with a different vendor and getting a lot of Bla-bla-bla for a while, I called Don at Air Flow Performance. Sure enough, he sells an 0.0275" restrictor (stock is 0.028"), for about $27. So I had him send me one and I gave it a try. PERFECT!
See the results before and after below:

gami tests.pdf


Hmmm, picture doesn't post. Well, the url is http://hpaircraft.com/rv8/gami tests.pdf and if you type that in a browser, it will show the plots

Don was super easy to work with, listened to my plan, said 'sure, no problem'. No muss, no fuss. A far different experience from the bla-bla-bla I got from another vendor.
 
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Thanks for the report. I have a very similar situation, seeing that it can get considerably better. I need to give Don a call and get er done...
 
While I plan to tune my injector nozzles with Don as well, I have to say that the "other vendor", which is no doubt GAMI, is outstanding. I've had 4 sets of Gamijectors on different planes, including a set of their turbo variety, I flew with them for years and would not hesitate to use them again. They are a lot more than "bla bla bla" in my experience.:rolleyes:
 
Yep---Don has the injections covered. If you havent taken his FI course---I HIGHLY recommend it. Alot of us have, and its worth every penny.
Tom
 
I got to do this soon. Haven't checked mr spread but it probably isn't terrible. But could be much better too. How,does one start the process with don?
 
Great job and definitely worthwhile, LOP ops are a good thing. However an actual "zero" spread is nearly impossible especially at various throttle settings, it's like trying to get a 0.000 ips prop balance, in reality it just ain't gonna happen, but depending on the equipment resolution, and if you're looking at only one specific "snap shot" in time, it may look close to "zero".
 
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Mark Dickens said:
While I plan to tune my injector nozzles with Don as well, I have to say that the "other vendor", which is no doubt GAMI, is outstanding. I've had 4 sets of Gamijectors on different planes, including a set of their turbo variety, I flew with them for years and would not hesitate to use them again. They are a lot more than "bla bla bla" in my experience.:rolleyes:
Click to expand...

NO I was not referring to GAMI. I have not spoken with them, but I hear of nothing but good things from them. I just didn't feel I needed to go the full GAMI service for an engine that was so close to perfect that tweaking one cylinder would do it. The other vendor was someone else.
 
Walt said:
Great job and definitely worthwhile, LOP ops are a good thing. However an actual "zero" spread is nearly impossible especially at various throttle settings, it's like trying to get a 0.000 ips prop balance, in reality it just ain't gonna happen, but depending on the equipment resolution, and if you're looking at only one specific "snap shot" in time, it may look close to "zero".
Click to expand...

I agree. Thats why I put it in quotes in the title. My fuel flow meter seems to be a bit g-sensitive, and otherwise not that consistent. Also this was at only one altitude -- 8200 ft, WOT. I will repeat the test at 11,000 next chance I get. But yes, settling time at each data point, altitude, turbulence, can all add uncertainty in the fuel flow measurement. What does seem to be pretty solid though are the temperature readings at a given throttle setting during a given test. So the peaks are the peaks, within the resolution of the 0.1 gph steps.
 
scsmith said:
So the peaks are the peaks, within the resolution of the 0.1 gph steps.
Click to expand...

It'd be waaaaay overkill, but sometimes I wish the various EFIS/EMS manufacturers would log the raw DN values instead of the converted values... :)
 
In addition to helping me with balancing injectors, Don was very helpfull in addressing my idle roughness in hot weather. He is VERY knowledgeable and offered many suggestion. Better still, his prices are quite fair and reasonable.

Larry
 
Don also helped me with my injectors and I had to replace only two of them for a closer balance. I can certainly not claim zero but pretty darn close spread when I go LOP.
Don't forget to mark the location of each nozzle so if you ever pull them for cleaning or otherwise to put them back where they belong.
 
just a thread bump. I wanted this to stay up through another cycle so more folks would see it. The plotted results on the first post are a PDF, which might be why they don't appear in the post. But take a look at the link.
 
Thank you Don

I just finished with an injector tuning effort and after the 3rd and final exchange of nozzles, I have all my EGTs peak at nearly the same time.
Well worth the effort.
 
Yes! :)

Michael Henning said:
Having tuned the injectors, do you notice the engine to be any smoother?
Click to expand...

Yes I do. In the past, once in a while when I get as lean as I like, I can feel a slight 'chugging' as if there is a light miss on a cylinder. Sometimes this would go away if I just tweaked the throttle plate closed a bit, maybe dropping 0.1 in. hg. Sometimes that wouldn't help. I would also notice when the plugs got about 80 hrs on them that it would miss more when lean.

Now, I can lean until it just about stops and is smooth with no detected roughness until it is about to quit. Time will tell if it is more tolerant of slightly dirty plugs.
 
Some data from my -4

I was inspired by this thread to look at my EGTs as a function of fuel flow, so this evening I climbed to 6500 feet and copied data from my Ultimate Engine Analyzer to a clipboard on my lap. Here's the graphed data (for the one and only run). I probably should do a few more runs at different altitudes and power settings, but is this spread acceptable for LOP operation?

2q1x6au.jpg


Dean
 
Correct - you need a series of runs to make sure you have good data. You are close but could be closer.

Assuming your one run represents actual conditions, and you have standard 0.028" injectors you have:

#1 & #2 peak first and about the same time. They are lean compared end to the rest.

#3 & #4 peak last and about the same time. They are rich compared to the rest.

So - you can reduce #3 and #4 injectors to 0.0275 or 0.027 and do another set of runs. From the new data you can refine the injectors again. It took me three injector configurations (IO-540) to get it just right. For this engine I started with a 1.5gph spread. It is now 0.1 if anything.

Carl
 
A couple of days ago, I made another test run. This time at 8000 feet with the throttle wide open. The spread appears to be a bit less (~0.2 gph), though the peaks are not as well defined. It may simply be that I was not as diligent collecting the data points. Either way, it seems I could replace a couple of nozzles to reduce the spread or leave well enough alone and run LOP when the mood strikes. I was surprised that throughout the data collection, by CHTs did not seem to change. (All remained stable with values between 290 and 315F.)

r8a6v7.jpg
 
Dean Pichon said:
A couple of days ago, I made another test run. This time at 8000 feet with the throttle wide open. The spread appears to be a bit less (~0.2 gph), though the peaks are not as well defined. It may simply be that I was not as diligent collecting the data points. Either way, it seems I could replace a couple of nozzles to reduce the spread or leave well enough alone and run LOP when the mood strikes. I was surprised that throughout the data collection, by CHTs did not seem to change. (All remained stable with values between 290 and 315F.)

r8a6v7.jpg
Click to expand...

HI Dean, I would say your results are 'acceptable' but could probably be improved on a little. l would be interested to know what engine you have and what manifold type (horizontal vs vertical). It looks like your manifold preferentially distributes more air to the back cylinders (#3,#4) so that they are a bit richer. Slightly leaner nozzles (0.0275) would lean those a bit, and might get you even closer.
My initial spread was bigger than yours and I put up with it for seven years. So you could just leave it. But a minor tweak of changing two nozzles (at about $27 each) may make your engine run really smooth LOP like mine does now.

I wish I had done this a long time ago.
 
I did mine a couple weeks ago. They were running about .3 gph spread and a little roughness LOP.

I sent Don 4 different runs worth of data and he recommended changing a couple nozzles. Now, .1 gph between all 4 peaking and it's much, much smoother LOP and I'm actually getting the same TAS running about .3gph less fuel flow.

Well worth the effort and small cost.
 
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