Sean Franklin
(Top Gun)
09/28/06 11:49 AM
GAMI's on a Skyhawk?

I have a 1998 Skyhawk - 180HP, Lycoming IO-360-L2A. A few months ago I had a JPI EDM-700 installed, and I've been learning a lot about how to run the engine to minimize CHT's. Mike Busch's column this week, "Temperature, Temperature, Temperature", got me to thinking about how I could coax a bit more performance out of my airplane.

When the JPI was installed, I found that a typical temp spread in cruise would range from 330-380F (coldest to hottest). At my next oil change, I found some loose baffle plates so I had my shop fix those. Now I'm seeing 340-370 spread. This is LOP, WOT, about 8.1GPH, 9,000'. I'm running around 2,450RPM and getting about 117kt TAS. This is a fixed-pitch prop.

The engine runs smoothly LOP, but what I'm wondering is if GAMI's would narrow the CHT spread a bit, and allow me to enrichen the mixture to get a bit more RPM / speed without increasing my hottest cylinder temp. Hottest cylinder is #3, followed by #4, so I guess what I'm asking is, is the 30-deg spread just "normal" for the back cylinders, or would GAMI's help? I'm willing to spend the $699 to gain a few knots.


Ed Williams [PHOG]
(Top Gun)
09/28/06 12:41 PM
Re: GAMI's on a Skyhawk?

Download the lean test form from GAMI and run the test to see whether your cylinders peak their EGTs together. If they already do, there's little to gain and vice-versa.

Sean Franklin
(Top Gun)
09/28/06 12:48 PM
Re: GAMI's on a Skyhawk?

I'll run the test. They don't peak together, I know that... probably 30-40 degree spread there (just from memory).

Ron Rosenfeld (EPM)
(Public Guest)
09/28/06 04:06 PM
GAMI's on a Skyhawk?

Sean,

<< probably 30-40 degree spread there >>

The temperature difference in EGT's is completely irrelevant to the test.
Thinking that it is is a very common error, though.

What you will be looking for is the fuel flow at peak EGT for each cylinder.

It matters not at all what the actual temperature is at peak EGT; only the
fuel flow.

So you find peak EGT for each cylinder and record the fuel flow at peak for
each. There's really no need to even record the temperature.

The "spread" is the difference in fuel flows.

Best,


Mark Pfeifer (KMAN)
(Public Guest)
09/28/06 06:57 PM
Re: GAMI's on a Skyhawk?

If you go into LOP lean mode .. after the last cylinder peaks, push and hold the right button .. the right hand number will be the 'spread' in gph between the 1st and last cylinders to peak.

GAMIs will give you 0.5 or less (probably less).


Joe Budge (W29)
(Top Gun)
09/29/06 02:37 AM
Re: GAMI's on a Skyhawk?

As much as I'm an enthusiast of GAMI's, don't focus on them to the exlusion of everything else. There can be plenty going on besides the fuel injectors. You fixed the loose baffle plates, which is good. You also want to check that plates aren't missing, bent, cracked, or have extra holes in them. Be sure to check the plates between the cylinders. Some of the bending and holes are on purpose, so if in doubt check against the parts diagrams and/or a similar-rev Skyhawk. Make sure the baffle seals are intact and still stiff enough to seal against the cowling. More in Mike Bush's article here.

Regards,
Joe


Sean Franklin
(Top Gun)
09/29/06 08:58 AM
Re: GAMI's on a Skyhawk?

Quote:

<< probably 30-40 degree spread there >>

The temperature difference in EGT's is completely irrelevant to the test.
Thinking that it is is a very common error, though.

What you will be looking for is the fuel flow at peak EGT for each cylinder.




Gotcha. My recollection is that the 1st to peak has gone lean by 30-40 deg. before the last peaks. Have to check on the FF's. I have downloaded the GAMI test chart and will fill it out this weekend.


Sean Franklin
(Top Gun)
09/30/06 06:32 AM
Re: GAMI's on a Skyhawk?

Quote:

If you go into LOP lean mode .. after the last cylinder peaks, push and hold the right button .. the right hand number will be the 'spread' in gph between the 1st and last cylinders to peak.

GAMIs will give you 0.5 or less (probably less).



OK, did a test flight last night. I'm getting a 0.2 spread, so GAMI's probably won't do much. I leaned down to 85LOP with no roughness, but was down to 2,000RPM by then so didn't go any further.

I'll check the baffles as Joe suggested, but likely if I want to go faster... I need a faster airplane :-D


Ed Williams [PHOG]
(Top Gun)
09/30/06 02:49 PM
Re: GAMI's on a Skyhawk?

With an 0.2GPH spread you're about as good as you can get. GAMIs won't do anything for you.

Ed


Paul Millner [OAK]
(Top Gun)
12/13/17 06:28 PM
Re: GAMI's on a Skyhawk?

Sean,

Did you ever get those CHTs closer together? Thanks to Walter and George’s smarts applied to the Cardinal, we know lots more on improving Cessna & Lycoming cooling!

Paul


Scott Dyer [HPN/NY]
(Top Gun)
12/14/17 08:35 AM
Re: GAMI's on a Skyhawk?

Paul -- Not sure Sean is flying any more, from what I've seen of his FB posts.

(Some kind of record, perhaps, an 11 year exhumation of a thread.....)


Gil Buettner [KAUW]
(Top Gun)
12/18/17 08:38 PM
Re: GAMI's on a Skyhawk?

Yes, I think he is no longer active in aviation.

Andrew Niemyer -KDLH
(Top Gun)
12/19/17 07:44 AM
Re: GAMI's on a Skyhawk?

He both bought and later sold his Saratoga through the same broker (Bartelt Aviation, Sturgis, MI) that I used for three transactions last decade. After that, he drifted entirely away from aviation, I think mainly due to job and family commitments. He still seems to be involved in his local theatrical scene, from his posts on FB.

Best,
Andy



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