GAMIjectors....

[Guy Paris]

Hey gang, anyone have any positive or negative results using Gami's in a nornal aspirated IO 360? Mine just happen to be a G and a GB.... Thanks. Guy... old72driver... (thanks for asking Larry, I wondered too)

[Ernie Martin]

Guy:

From lengthy and controversial discussions on this subject, held over various Skymaster websites, you're gonna get two views. One side, including GAMI, believes that the ultra-precise injectors, custom drilled for each cylinder based on the heat of that cylinder (where it is on the engine), allows you to operate the aircraft safely at considerably lower fuel flow rates, thus saving lots of money. Specifically, these advocates believe that you can operate 50-100 dgrees LEAN of peak (you read that right, you lean the engine to peak EGT and then lean it some more).

A vociferous group of opponents claim that such operations, even with GAMI injectors, is an accident waiting to happen, because it will damage the engine and possibly cause an in-flight failure leading to a disaster. They further add that because you are not operating the engine per the POH (which forbids operation any leaner than 50 degrees rich of lean), if the engine fails there is no warranty. And they conclude by pointing out that the cost of these injectors is so high that it is hard to recoup the expense in fuel savings for the average pilot.

I'm a mechanical engineer (Master's from Caltech, spent 20 years on satellites and rockets and 10 years on jet engines) and have at times tried to referee this argument. Here's my take: the latter group -- the opponents -- are more right than the lean-of-peak (LOP) advocates. For average and even technically savvy pilots, they ought to stick with the factory recommendations. There are lots of documented cases where indeed LOP operation has led to failed engines; often NOT BECAUSE of LOP but because the pilot did not devote the additional attention needed for LOP operation.

Let me say it a different way. The POH way is rugged and tolerant of mistakes. Lets you fly the plane and enjoy the ride. LOP might work as GAMI and its advocates claim if ALL of the following things are just right: the right injectors were properly installed and checked out, a cylinder-by-cylinder diagnostic monitoring system is on board, and the pilot follows LOP procedures correctly AND monitors each cylinder like a hawk during each flight.

Since I'd rather enjoy the flight than act as a flight engineer, I opt for following the POH, and have done so in the two Skymasters I've owned.

Ernie Martin

[Bob Cook]

1) Having an engine analizer is MANDATORY above 65% power settings.
2) You can tweak or play with injectors to bring then closer to cylinder matching. Using the GAMI form to see how close they are.
3) You can run safely LOP below 68% power with proper monitoring.
4) normal aspirated engines are less worrisome.
5) Without monitoring you can run below 60% power by leaning until rough and then enrich by 1/2 gph or until smooth.

major concern is pre-detonation or high cyl head temps. Both these conditions CANNOT occur below 65% power. the engine will TELL YOU if it likes the fuel flow or not.

You increase potential for carbon deposits and increased moisture in oil due to low engine temperatures. Make sure your oil temps stay above 16 degrees if at all possible and closer to 190 would be more preferable.

It is not rocket Science...... (sorry for pun)

Bob

[Guy Paris]

Bob and Ernie, thanks for the response. I had NO intention of ever running lean of peak.

I too was (am) an engineer of sorts, I was a flight engineer on the Convair 880 and the Boeing 727 many years ago. Learned back then the manufacture knew a heck of a lot more than I would ever know or have to know.... When I upgraded to the left seat and someone wanted to deviate from the norm I would stop it in its tracks, tell them to go to the company and see if they agree and have it changed....

I was just wondering if having more balance in the F/F at peak EGT is worth the cost and effort for engine health. My POH states that I can run at peak EGT if (The Cessna Economy Indicator EGT) is installed and operating at 65% or less. My JPI 760 tells me that total F/F as each cylinder peaks that there are differences. Guy, old72driver....

[Ernie Martin]

Guy:

First, a question. When you say that "My POH states that I can run at peak EGT if one is installed and operating at 65% or less", what needs to be installed? An engine analyzer?

Even at 65% (or less) I'm surprised that your POH authorizes peak EGT operation; both my 337D and my 337G prohibited it, except for short durations to establish peak EGT for reference. You might want to look at your POH again to be sure that it's OK for long periods.

Ernie

[Guy Paris]

Ernie, on said page it states: LEANING WITH A CESSNA ECONOMY MIXTURE INDICATOR (EGT)... (would have to say a far cry from an engine analyzer)

1st paragraph talks about 75% power or less and references figure 4-4 EGT table and recomended lean of 50% rich of peak.

**Opps, the above should read 50 degrees F Rich Of Peak EGT**

2nd paragraph says: Continuous operation at peak EGT is authorized ONLY at 65% power or less. This best economy mixture setting results in approximatly 8% greater range than shown in this handbook accompanied by approximatly a 4 kt decrease in speed.

Then there is a note: Operation on the lean side of peak EGT is NOT approved.

Hey, what can I say, I am the end user, this is what is in my POH... Cessna Model 337 G Ser.# 1805... Guy. old72driver....

What year is yours Ernie? The front of my POH states 1977 MODEL 337G

[Bob Cook]

Guy

The POH is correct. You should compare these figures with the actual TCM engine manual supplied by Continental. The economy settings indeed are PEAK based on the fuel flow stated by Cessna.

There are differences when each cylinder peaks and that is caused by differences in fuel flow. Tighter control or matching of injector nozzles can improve performance by allowing the engine to peak on ALL cylinders closer to peak.

50 ROP is somewhat lean and most recommend going 60 ROP at above 68% power.

You can find which injectors peak first and last then swap injectors. Move them around until the least differencial is seen on the engine monitors.

Personally, I do not believe that running the Gami injectors are going to buy you anything unless you do intend to run LOP.

You can buy a lot of fuel for the price of a set of Gami's.

Go to the Gami sight and download the "test" and see where you stand. At least it can tell you how close your injectors are.

You cannot hurt your engine below 65% power as long as it is running "smooth". In fact I can run down to < 10 gph and still run very smooth.

More damage can be caused running <50ROP at higher power settings. This includes rapid cooling and putting a load on a cold engine. Running lean (when able) certainly helps to keep carbon deposits to a minimum and your oil much cleaner for a longer period of time.

It's your call..

Bob

[MikeZ]

I've been running my 79 P337 for 14 years now. I have Riley intercoolers. In the "old" days I used to lean aggressively, but still within the book numbers, modified by Riley. Burned through many cylinders. Eventually I reached the conclusion with my maintenance manager that I was running too lean. So since being a little more generous with fuel, and giving a bit more fuel on climb, I stopped burning through cylinders for years now. If I choose to use less GPH, I'll just cut the power setting back, open my POH, go to the altitude/performance tables, and see what my fuel burn should be at that power setting. Then I fly the settings. I think trying to save fuel by paying for GAMI injectors is the wrong end of the telescope. Save fuel by flying at less power, and save the engine by running a bit richer.

mike zinn

[Guy Paris]

Thanks Bob and Mike Z.
A while back I spent some time leaning each cyl. to see what was what.

Front eng.
Cyl. #1 peaked at 1420 and total F/F of 8.4 (least)
Cyl. #5 peaked at 1430 and total F/F of 9.5 (most)

Rear eng.
Cyl. #2 peaked at 1420 and total F/F of 8.5 (least)
Crl. #5 peaked at 1430 and total F/F of 9.7 (most)

The cyl. in between went progressivly higher.

I will check the Gami site and see where I stand. In the 10 plus years I have had my bird I have had to change one cyl. and that was an O/H one that was installed when I first got her. (a welded repair). Next time I am in the shop I will consider swaping the leaner with the ritcher, although both engines are relativly close in numbers, it leads me to believe it just might be the nature of the beast. Guy, old72driver....

[Bob Cook]

Guy

you are not that bad. take a Gami "test" and see where you stand. On the JPI my max cht differential is about 40 degrees when leaned properly. at idle it is over 135 deg diff.

there is an inherent difference if fuel flow requirement with the rear cylinders requiring slightly larger FF (if I remember correctly). This is where Gami comes in. they have been able to figure out the exact cyl requirements (experience) and are able to get it close. Guess the manifold / fuel lines are not quite equal length.

They still need to tweak the odd cylinder and it comes down to trial and error if it doesn't quite "make it"

bob

[hharney]

The standard unit that JPI sells for twins is the 760. I know that many of you have these installed and they are working well. Is the 20 ft standard lead enough for the rear engine access? JPI was not sure there was any special length for the 337 and that the standard kit (20 ft) would be sufficient.

Let me know if this is different for the rear engine installation.

[Dave Underwood]

Time for my two cents worth.

1) As I recall, there is a slightly longer harness for the EDM760 to accomidate the 337 and the distance to the rear engine. The folks at JPI are good and will answer questions.

2) I installed Gami's a couple of years ago as part of a project to get the aircraft running smoother. They do make a difference and I can see that on my EDM760 on the EGT display as I lean. The engines start and run more smoothly, no question.

3) I also dynamically balanced both engines which also helped smooth things out a bit. Certainly there is much less rock and roll now. I figure vibration will be the biggest enemy as our aircraft age.

4) I tend to climb at the top of the green full rich, which as I'm in a turbo is important. In cruise I fly at 55% or 65%, generally slightly LOP. My experiences lean of peak are that it does save a bit of fuel, but not as much as I was hoping. That said, I have other friends that swear by it, but they are running bigger engines with greater fuel flow savings.

5) I suppose all things being equal, I save about 1 +/- gal/hour/engine and Ernie is right, it does take some management. It also takes some experience to feel comfortable with the process, but the engines do run smoother and cleaner.

6) Fuel around here (in the UK) is $8.00/gal or more which means a payback in less than a year (100 hours +/-). It also increases the safety margins on long legs and if you were in real trouble you could power way back and stay airbourne for many extra hours at very low power settings.

7) In summary, I figure it was worth it.

Regards - Dave

[hharney]

Dave
Thanks for the response. I talked with JPI and the person I talked to at Sun N Fun could not remember if there was a special need cable length for the rear engine. Sounds like I will need to make sure before I purchase in Oshkosh this year. I just installed the GAMI's last month and will be doing the JPI after Oshkosh. JPI has some nice incentives on buying at the shows. $300 rebate for the 760 + $300 rebate for the fuel flow option and 2 free probes of choice (I will choose the oil temp probes. It has to be purchased from a authorized distributor so I had 4 out of 5 at SNF shoot me a quote for the 760, 6 cyl, with fuel flow. Here are the results:

Gami $4908.00
Gulf Coast $5100.00
Sarasota Avionics $4535.00
Spruce $4816.70

Retail is $5895.00


Quite the spread but I will see how hungry they are in OSH. This is before the $600 rebate and the oil temp probes are $165 each.

Best price with rebate and the 2 free probes $3935.00