High GAMI spread, strange CHT drop during leaning

Hello

My buddy has a RV-7A with an Aerosport IO-320, turning an Sensenich metal FP since about 200 hours. The fuel injection is a Silverhawk unit.

He told me a few times that something seams not as it should be. I looked at the data and do not get the cloue what it can be really.

I told him to make a GAMI spread, here the results:


The spread is in liters, here the equivalent in USG:
24.5L = 6.47 USG
22.0L = 5.81 USG
21.0L = 5.54 USG

After this, he cleaned the nozzle 1 and 3, but this did noch changed the situation.

I think we contact Don Rivera and get other nozzles.

One other thing, I found, when he is leaning, the cylinder 3 CHT drops by about 40 to 50?F, the others stay together more even. When he enrichen the mixture, cylinder 3 CHT comes back quickly!?
Picture when cyl 3 CHT drops (EGT top row, CHT bottom row):


And here when it comes back (cyl 3 is yellow here):


Does he run it too lean, so that cyl 3 is allready on the lean side of the peak? Here he has it at about 25L (6.6 USG) and past time 00:10 at 28L (7.3 USG).

Any idea why CHT drops that much and how to proceed with the high GAMI spread, are welcome.

In the mean time, we switched from magnetos to 2x PMAG, but this did not changed the situation, just easyer starting and better performance.

Best regards and thanks!

Dominik and Roland

Cyl 3 is running much leaner than the others, so you want to get a bigger nozzle. His stock is probably a 0.028", so I would get a 0.029" and a 0.0295" nozzle. You could, instead, get 2 0.027" and 2-3 0.0275" and lean out the other cylinders.

With #3 running lean, it is getting much further past peak in a lean test, so it is losing a lot of power, hence cooling way at should be fixed with tuning the restrictors.

Induction Leak

Jesse said:

Cyl 3 is running much leaner than the others, so you want to get a bigger nozzle. His stock is probably a 0.028", so I would get a 0.029" and a 0.0295" nozzle. You could, instead, get 2 0.027" and 2-3 0.0275" and lean out the other cylinders.

With #3 running lean, it is getting much further past peak in a lean test, so it is losing a lot of power, hence cooling way at should be fixed with tuning the restrictors.

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If the GAMI test was not done at full throttle, I would investigate an induction leak on cylinder 3 before messing with injectors.

Skylor

skylor said:

If the GAMI test was not done at full throttle, I would investigate an induction leak on cylinder 3 before messing with injectors.

Skylor

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An induction leak will not make nearly as much difference in a fuel injected engine as it will in a carburated engine.

I do agree, though, that the Gami test should be done at a cruise power setting.

swisseagle said:

My buddy has a RV-7A with an Aerosport IO-320, turning an Sensenich metal FP since about 200 hours. The fuel injection is a Silverhawk unit.

He told me a few times that something seams not as it should be. I looked at the data and do not get the cloue what it can be really. I told him to make a GAMI spread, here the results:

The spread is in liters, here the equivalent in USG:
24.5L = 6.47 USG
22.0L = 5.81 USG
21.0L = 5.54 USG

After this, he cleaned the nozzle 1 and 3, but this did noch changed the situation. I think we contact Don Rivera and get other nozzles.

Click to expand...

Issue here is trying to do a GAMI spread on a 320 at 13,250 feet. Nozzle tweaking won't help; fuel flow is too low. I'm sure Don will explain when you contact him.

Thank you!

Hello Jesse, Skylor and Dan

Thank you for your answer and inputs.

He will do another measure flight this week, according to the instruction from Don: http://airflowperformance.com/wp-content/uploads/2015/12/Nozzle-Tuning-Instructions.pdf

I told hin in the beginning to do it on 8000ft DA ... no clue why he was going so high ...

With the Sensenich metall FP it is difficult to get full power, the RPM limit comes early! Around 5000ft, you can not give more than 70% Power, or you will go past the RPM limit.

Waiting for new data and will report here.

Best regards, Dominik

swisseagle said:

He will do another measure flight this week, according to the instruction from Don: http://airflowperformance.com/wp-content/uploads/2015/12/Nozzle-Tuning-Instructions.pdf

I told him in the beginning to do it on 8000ft DA ... no clue why he was going so high ...

With the Sensenich metal FP it is difficult to get full power, the RPM limit comes early! Around 5000ft, you can not give more than 70% Power, or you will go past the RPM limit.

Click to expand...

Those instructions suggest initial tests at 3500 ft and 24/2400 for a reason. To judge restrictor balance with any accuracy, he must generate enough power to push fuel flow into the 7~8 GPH range or higher at peak EGT. That's easy with a big motor, but requires dense air and some RPM with a little 320.

Assume the pilot sets an honest 75% by the book, which assumes Best Power mixture. Actual power drops off as mixture is moved from best power mixture to peak EGT, so the book MP/RPM for 75% probably doesn't generate more than 70% at peak. Ok, 70% of 160 (IO-320 Lycoming) is 112 HP. BSFC at peak is around 0.42 lbs/HP/hr, so (112 x 0.42) / 6 = 7.84 GPH.

Turn the equations around and the previously posted fuel flows (around 6 GPH) tell us your friend was at (ballpark) 54% power.

So why is this important? The little inserts in the nozzles are called restrictors for a reason. At higher fuel flows, tweaking the diameters actually changes the restriction to flow, and thus the distribution of fuel to individual cylinders. However, as flow is reduced, the variable area of the passageways in the flow divider becomes more and more dominant. With standard 0.028" restrictors, fuel division around 6 GPH is transitioning to the flow divider. Swapping nozzles won't change much.

Don, you out there? I seem to recall excel spreadsheets calculating the line pressure increase with a set of 0.022" restrictors?

I just had a private note from Don Rivera. Apparently he and Coleen decided to stop buying advertising on VAF...and as a result, he is no longer allowed to post here, even as a private party under a new, non-business screen name.

I've been running my store 28 years, so I completely understand the need to prohibit non-advertisers from offering products and services to VAF readers. Business is business; Delta Romeo LLC must make money, or it can't stay on the web.

However, "Advertise or be banned" seems a bit excessive.

We have hundreds, if not thousands of business owners on VAF, and we all manage to post contributions without pumping our respective products and services. is there some reason to believe Don can't meet that standard? Sure seems like a major loss of knowledge to ban him without an opportunity to demonstrate he is at least as ethical as the rest of us.

I have benefitted from Don's input here in the forum in the past and cant imagine why his input wouldn't be welcomed here. What the heck?

erich

DanH said:

I just had a private note from Don Rivera. Apparently he and Coleen decided to stop buying advertising on VAF...and as a result, he is no longer allowed to post here, even as a private party under a new, non-business screen name.

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This explains why I did not see any mention of their upcoming class that I plan to attend. Heard it through the grapevine

Raymo said:

This explains why I did not see any mention of their upcoming class that I plan to attend.

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And you wouldn't in the future if Don remained a non-advertiser, which is not unreasonable.

DanH said:

I just had a private note from Don Rivera. Apparently he and Coleen decided to stop buying advertising on VAF...and as a result, he is no longer allowed to post here, even as a private party under a new, non-business screen name.

I've been running my store 28 years, so I completely understand the need to prohibit non-advertisers from offering products and services to VAF readers. Business is business; Delta Romeo LLC must make money, or it can't stay on the web.

However, "Advertise or be banned" seems a bit excessive.

We have hundreds, if not thousands of business owners on VAF, and we all manage to post contributions without pumping our respective products and services. is there some reason to believe Don can't meet that standard? Sure seems like a major loss of knowledge to ban him without an opportunity to demonstrate he is at least as ethical as the rest of us.

Click to expand...

Not trying to stir the pot but......man that kindda bites.