NicoN

Question on GAMI-injectors

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My M20K has GAMI-injectors. After cylinder exchange I am not sure, if there is need to do something with them.

I have not payed much attention on the GAMI things, so let me ask maybe stupid questions.

- AFAIK GAMI-injectors means that you buy a set of matched injetor nozzles which tend to have all the exact same fuel flow.

- Friends are of the opinion that they are not "matched" for the same FF, but  calibrated to a special cylinder

therefore:

  • you cannot change them between cylinders (?)
  • after cylinder change/repair the calibration effect is gone

Indeed, after the cylinder change, we see quite bigger differences in EGT and CHTs. Especially #2 Cyl is about 50°F hotter than the others.

Flying LOP about 70° nearly wipes the differences out.

 

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On 2/28/2019 at 6:17 AM, NicoN said:

My M20K has GAMI-injectors. After cylinder exchange I am not sure, if there is need to do something with them.

I have not payed much attention on the GAMI things, so let me ask maybe stupid questions.

- AFAIK GAMI-injectors means that you buy a set of matched injetor nozzles which tend to have all the exact same fuel flow.

- Friends are of the opinion that they are not "matched" for the same FF, but  calibrated to a special cylinder

therefore:

  • you cannot change them between cylinders (?)
  • after cylinder change/repair the calibration effect is gone

Indeed, after the cylinder change, we see quite bigger differences in EGT and CHTs. Especially #2 Cyl is about 50°F hotter than the others.

Flying LOP about 70° nearly wipes the differences out.

 

Listen to your friends. A better way to look at it is that GAMIs are tuned to your engine’s intake. The goal is to produce similar F/A ratios to each one of the six, single cylinder engines you’re trying to manage with just one throttle and one mixture control.

Edited by Shadrach
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With flight testing on an engine, injectors are swapped to achieve a more perfect balance between cylinders when leaned. Probably cylinder change would indicate rerunning the GAMI test to verify balance.

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10 minutes ago, BDPetersen said:

With flight testing on an engine, injectors are swapped to achieve a more perfect balance between cylinders when leaned. Probably cylinder change would indicate rerunning the GAMI test to verify balance.

I doubt that much will change especially in a turbocharged engine but it’s a good idea to check.

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1) First time you lean the engine... check your Gami spread...

2) If it is still tight, everything is good...

3) if it is wide, something changed... check the logs to see what injectors were used on which cylinders... it is possible a mechanic is unaware that you have matched injectors and cylinders...

4) Flow matching starts with the intake, but finishes in the cylinder, all the way out to the exhaust....

5) If you change out identical cylinders for identical cylinders, there probably won’t be a difference...

6) If a new cylinder gets used, and it has its treatment of being ‘ported and polished’ different than the others... you might expect a change.

7) 70°F LOP, That is typical of a pretty tight Gami spread... (see Jack’s note above)

8) Expect to be able to compare before and after Gami spread data... if you get a change you didn’t expect... that starts the process of finding out what changed...

9) In the worst case, Gami can make suggestions that may include moving what you have around... or swapping in different injectors...

10) It all starts with capturing good data...

Good luck, report what you find out...

PP thoughts only, not a mechanic...

Best regards,

-a-

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1 hour ago, NicoN said:

Edited/cut to focus on a few of the topics.....

- AFAIK GAMI-injectors means that you buy a set of matched injetor nozzles which tend to have all the exact same fuel flow.

- Friends are of the opinion that they are not "matched" for the same FF, but  calibrated to a special cylinder

therefore:

  • you cannot change them between cylinders (?)
  • after cylinder change/repair the calibration effect is gone

Indeed, after the cylinder change, we see quite bigger differences in EGT and CHTs. Especially #2 Cyl is about 50°F hotter than the others.

Flying LOP about 70° nearly wipes the differences out.

 

Nico,

You have some smart friends... but...

The reason for special fuel injectors... they match the FF to the air flow in that cylinder....

they are not the same FF!  (Because the airflow is not the same, for various reasons)

They are calibrated to be different FF.  To match the inherently different airflow...

What we want... is that all cylinders peak at the same FF... by matching the air/fuel ratio...

raw EGT data is less helpful, as always... but in this case, you know what it was before, no differences were expected, but you got a difference....

Going deep LOP has a hard time of wiping out the differences... with a wider Gami spread, one of the cylinders will stop firing before all the others...

Any better?

Trying to describe this by typing...is probably not very helpful. But, It’s the best I can do... :)

If you understand what I wrote... you are really good... now go back to your friends and discuss balancing FF, to airflow, to maintain air/fuel ratios....

Continental did a nice job on the air intake system design for the K... the airflow is generally nicely balanced.... so the FF variations between cylinders isn’t very great.... the Gami’s don’t have as big of a challenge to start with...

Best regards,

-a-

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Thank you!

Next step will be to do the GAMI-test as Savvy recommend again and get some good data out of the EDM830

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Nico, You have some smart friends... but...

The reason for special fuel injectors... they match the FF to the air flow in that cylinder....

they are not the same FF!  (Because the airflow is not the same, for various reasons)

 

 

I’ll respectfully disagree with a detail here but not the intent. The air/fuel imbalances are not cylinder dependent. Each cylinder has exactly the same bore and stroke and hence a very equal draw of air - all things equal. They also have a predictable fuel pattern flow past the injector. It is the differences in the intake manifold length, turbulences within, and pressure timing as the intake valve opens that the folks at GAMI correct for by precisely adjusting fuel flow. This is why they don’t care anything about the cylinders you have installed when they send you the first set (which in my experience often is right-on for non turbo engines). They base the first set on years of data from the various engines they support.

 

A cylinder change, unless it corrected for an unknown intake leak should not adversely affect the original fuel distribution spread.

 

 

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10 hours ago, DVA said:

 

I’ll respectfully disagree with a detail here but not the intent. The air/fuel imbalances are not cylinder dependent. Each cylinder has exactly the same bore and stroke and hence a very equal draw of air - all things equal. They also have a predictable fuel pattern flow past the injector. It is the differences in the intake manifold length, turbulences within, and pressure timing as the intake valve opens that the folks at GAMI correct for by precisely adjusting fuel flow. This is why they don’t care anything about the cylinders you have installed when they send you the first set (which in my experience often is right-on for non turbo engines). They base the first set on years of data from the various engines they support.

 

A cylinder change, unless it corrected for an unknown intake leak should not adversely affect the original fuel distribution spread.

 

 

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Since we’re picking nits. Both Lycoming and Continental typically have remarkably consistent airflow from cylinder to cylinder. The issue more often than not is the log runner intake manifolds (Continental) that supply air to each bank of cylinders. Fuel from the first cylinder in the bank migrates backwards into the manifold when the intake valve closes. That means the air moving to the next cylinder gets a little fuel from the first cylinder in the bank. The last cylinder is getting a little fuel from the both the first and second. Therefore Continentals tend to get richer from first to last cylinder on each bank. GAMI solves this by reducing injector flow from first to last. Most injected, NA Lycoming with the tuned intakes do not require GAMIs. I’ve heard that there are stock Lyc IO360s that don’t run well LOP but I’ve never met one. My A1A has stock injectors and will run smooth well past 100LOP. This is not an exception with these engines but more the rule.

Edited by Shadrach
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Some of the confusion might be people with different engines. They are cylinder position specific. However on my io550, the initial set was not. They are all the same and not marked for cylinder location   

I haven’t had a chance to do the full gami test, which might lead to a cylinder specific swap, since the install. 

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If your GAMI test on your stock engine shows you are close enough on the fuel flows where they peak, don't buy them. If not, send GAMI the result of you test. "Standard" GAMIs for the continental, are sold with a pair for the front cylinders, a pair for the middle cylinders, and a pair for the rear ones. This is done to match what GAMI figured out generally worked from testing on many Continental engines. If your GAMI spread with the standard ones is not good enough, they will swap you more closely tailored ones for your particular cylinders. 

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Six cylinders is more challenging than four to have a good balance...

 

How you know the intake has been balanced for uniform airflow....

 

The intake tubes look curvy and snake like...

https://en.m.wikipedia.org/wiki/Continental_IO-550

 

The Lycoming six cylinder looks more organized with its log...

https://www.pennyanaero.com/lycoming-io-540-aircraft-engines

 

Apparently looks are deceiving...

 

I bet Clarence runs the IO720 ROP...  :)

Best regards,

-a-

 

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39 minutes ago, hypertech said:

Some of the confusion might be people with different engines. They are cylinder position specific. However on my io550, the initial set was not. They are all the same and not marked for cylinder location   

I haven’t had a chance to do the full gami test, which might lead to a cylinder specific swap, since the install. 

What is the benefit to buying gami injectors if they are not tuned? 

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What is the benefit to buying gami injectors if they are not tuned? 


Good question, because this thread is centering around only aspect of the GAMI injectors; tuning based on cylinder location. The other and very significant GAMI feature is consistency. These injectors are very precise and manufactured to very tight tolerances. The factory injectors are often inconsistent and as such one cylinder may get more of less fuel than another.

So in engines that GAMI has evaluated to have a fairly good and even airflow intake system (rare) a marked improvement may be seem just by installing precisely accurate injectors.

Does that make sense?


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a very precise injector is what? a piece of metal with a hole in it. The size of that hole is what is important, which can be precisely drilled by even a Harbor freight drill press ;) using the right drill bit.

A precisely sized injector for the individual intake system is what your after. This is done by measuring fuel flow to obtain the sizing and would be more precise using a flow bench.

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a very precise injector is what? a piece of metal with a hole in it. The size of that hole is what is important, which can be precisely drilled by even a Harbor freight drill press  using the right drill bit.


You’d find strong argument against that comment by those skilled in the art of fluid engineering - which is not me. But that’s why forums like this are entertaining to follow I guess. Smh.


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2 minutes ago, DVA said:

 


You’d find strong argument against that comment by those skilled in the art of fluid engineering - which is not me. But that’s why forums like this are entertaining to follow I guess. Smh.


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yea, they would appreciate the comment about being precise with a flow bench however.

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yea, they would appreciate the comment about being precise with a flow bench however.

 

Like the flow bench shown here?

 

http://

 

 

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25 minutes ago, DVA said:

 

Like the flow bench shown here?

 

http://

 

 

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Nope, it doesn't have the particular cylinder and intake system set up to measure.  Here is a flow bench

https://www.superflow.com/aspx/prodDetail.aspx?prodid=17&catid=4&navid=10

 

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4 hours ago, DVA said:

 


You’d find strong argument against that comment by those skilled in the art of fluid engineering - which is not me. But that’s why forums like this are entertaining to follow I guess. Smh.


Sent from my iPhone using Tapatalk

 

I think that George Braly or Jean Paul would both tell you that the stock injectors are quite precise. They are not however tuned to the intake.  Indeed the way GAMI controls flow is by varying the orifice size of each injector.  We can agree that using a harbor freight bit and a drill press is sub optimal...

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11 hours ago, Shadrach said:

What is the benefit to buying gami injectors if they are not tuned? 

On my K model, just installing the "standard" GAMIs made the engine considerably smoother. So good, no further tuning was required.

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On 3/1/2019 at 4:48 PM, DonMuncy said:

On my K model, just installing the "standard" GAMIs made the engine considerably smoother. So good, no further tuning was required.

By “standard” are you suggesting that all the injectors are flowed the same? GAMI has been doing this for so long that they can predict how to tune the injectors by engine model. They don’t always require further tuning. Cont TSIO360s likely have standard imbalances that GAMI is well aware of.

Edited by Shadrach
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6 minutes ago, Shadrach said:

By “standard” are you suggesting that all the injectors are flowed the same? GAMI has been doing this for so long that they can predict how to tune the injectors by engine model, They don’t always require further tuning. Cont TSIO360s likely have standard imbalances that GAMI is well aware of.

Flowed the same? No. GAMI has tested enough TSIO 360s, that their "standard" is a pair for the front cylinders, another pair for the middles and another pair for the rears. So yes, they are tuned in one sense and standard in another.

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I had GAMI install the tuned injectors in my TSIO-360 and just the "standard" set got my spread from 0.7 - 0.8gph down to .4-.5.  This was "good enough" but since I flew-in for the day to have them installed, they pulled one of them out and got the outlier to bring back in to get the spread down more.

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