Proper Fuel Flow for IO-360

[bradp]

I'm not sure why but I've glanced down at FF during takeoff roll and I'm seeing 18.4 on the last two observations.  I've historically thought of it as appx 18gph for my A3B6.

[Marauder]

Timing set at 20 or 25BTDC?

20


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[Marauder]

During the takeoff run:

2000' AGL:

[Shadrach]

1 hour ago, Marauder said:

 

20


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That’s why your CHTs are low. That engine is leaving a noticeable amount of takeoff and climb performance on the table....or maybe not since it’s running a mixture closer to best power than most. When was the servo last overhauled? I’m wondering if a mechanic in the past didn’t treat a low fuel flow/high CHT problem by retarding the timing.

Edited July 10, 2018 by Shadrach

[Marauder]

That’s why your CHTs are low. That engine is leaving a noticeable amount of takeoff and climb performance on the table....or maybe not since it’s running a mixture closer to best power than most. When was the servo last overhauled? I’m wondering if a mechanic in the past didn’t treat a low fuel flow/high CHT problem by retarding the timing.

Now you got me wondering. Terry (N6458N)checked my timing when we replaced the mag harnesses. I’m pretty sure it was 20° but you got me walking downstairs 12:42 AM to see what he put in my logs!

Servo was services around 1000 hours ago.


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[Marauder]

Went back 10 years, all shops that worked on it during that timeframe (4 of them including an MSC and Terry) all set the timing to 20°. A few referenced “engine timing set IAW Lycoming MM”.

As for takeoff power, I’ve flown in a number of F and J models. Hard to gauge apples to apples since I have speed mods and a decent rigging, but I am climbing as well or better than the Fs and my cruise speed is in the 152 KTAS to 154 KTAS range depending on loading. I am usually at full fuel.

Not sure if it is set incorrectly but I can’t complain about the temps or the performance.




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[carusoam]

For comparison...

310hp IO550 has a documented FF of 27.2 gph... the STC actually gives a range in LBs/hr...  the number I gave is the max end of the range.

Many prefer to bump the FF up a gallon or two per hr... for additional cooling, and climb out at full power...

timing is 22°BTDC

Best regards,

-a-

 

[amillet]

My home airport is 151 feet.  I see 18.6 gph on take off

[ArtVandelay]

That’s why your CHTs are low. That engine is leaving a noticeable amount of takeoff and climb performance on the table....or maybe not since it’s running a mixture closer to best power than most. When was the servo last overhauled? I’m wondering if a mechanic in the past didn’t treat a low fuel flow/high CHT problem by retarding the timing.

Those of us with A3B6 engines don’t have a choice, it’s plated for 20°. Noticeable? Can’t be that much, otherwise the engine would not make close to rated horsepower, and would fail certification tests.

[Bob_Belville]

I spent several days investigating the 20^o vs 25^o issue 6 years ago. Mine has a 20^o data plate and that is correct. The Lycoming specs are confusing. 

https://generalaviationnews.com/2012/05/08/ask-paul-what-is-the-correct-timing-for-my-engine/

[jetdriven]

2 hours ago, teejayevans said:

Those of us with A3B6 engines don’t have a choice, it’s plated for 20°. Noticeable? Can’t be that much, otherwise the engine would not make close to rated horsepower, and would fail certification tests.

There was no certification test and No dyno.  They simply created a service instruction out of thin air that said it was optional.  Instead of addressing the real issue of poor baffling on the Grumman Tiger.  I’ve ran them both ways and 20° Gives up performance (especially LOP) in exchange for a small CHT reduction.  I’d say that losing 6kt going to 20 degrees LOP vs. 2kt is pretty substantial. 

Edited July 10, 2018 by jetdriven

[Marauder]

3 hours ago, Bob_Belville said:

I spent several days investigating the 20^o vs 25^o issue 6 years ago. Mine has a 20^o data plate and that is correct. The Lycoming specs are confusing. 

https://generalaviationnews.com/2012/05/08/ask-paul-what-is-the-correct-timing-for-my-engine/

Thanks for posting the article Bob. I actually have Lycoming's operator's manual he mentions (Lycoming Operator’s Manual P/N 60297-12). Interestingly, I cannot find Service Instruction 1325A on the Lycoming site. Hmmm... Based on the article, my serial number should have been set to 20 degrees. 

I did find an interesting section on oil temps and pressures. So my 180 degree temps are not out of line. Also says idling oil pressure is fine at 25 PSI and I was worried about it idling at 56 PSI.

[Shadrach]

6 hours ago, teejayevans said:

Those of us with A3B6 engines don’t have a choice, it’s plated for 20°. Noticeable? Can’t be that much, otherwise the engine would not make close to rated horsepower, and would fail certification tests.

It’s not “that much”, but is indeed a defacto derating of the the engine.  I think the difference would become quite a bit more apparent at high altitude fields.

It’s was a way to treat the symptom of elevated CHT but did not cure the problem.

Edited July 10, 2018 by Shadrach

[Shadrach]

10 hours ago, Marauder said:

Went back 10 years, all shops that worked on it during that timeframe (4 of them including an MSC and Terry) all set the timing to 20°. A few referenced “engine timing set IAW Lycoming MM”.

As for takeoff power, I’ve flown in a number of F and J models. Hard to gauge apples to apples since I have speed mods and a decent rigging, but I am climbing as well or better than the Fs and my cruise speed is in the 152 KTAS to 154 KTAS range depending on loading. I am usually at full fuel.

Not sure if it is set incorrectly but I can’t complain about the temps or the performance.




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I’m not far off if you ever want to see how a box stock, time capsule set at 25BTDC compares.

Edited July 10, 2018 by Shadrach

[Bob_Belville]

48 minutes ago, Marauder said:

Thanks for posting the article Bob. I actually have Lycoming's operator's manual he mentions (Lycoming Operator’s Manual P/N 60297-12). Interestingly, I cannot find Service Instruction 1325A on the Lycoming site. Hmmm... Based on the article, my serial number should have been set to 20 degrees. 

I did find an interesting section on oil temps and pressures. So my 180 degree temps are not out of line. Also says idling oil pressure is fine at 25 PSI and I was worried about it idling at 56 PSI.

Yeah, I noticed that idle spec recently as well. I plotted oil pressure vs oil temp on Savvy for my recent flights and as you'd expect the curves move in the opposite direction. When the OT gets high the OP bumps the 60 psi bottom of the green. 

[Marauder]

I’m not far off if you ever want to see how a box stock, time capsule set at 25BTDC compares.

Let's race! Stinky Pants never took me up on it. I did have one race with a 68 F. He left an airport 6 minutes before I did. I caught him about 10 miles from our home airport which was about 70 nm away.

 

 

[Shadrach]

3 hours ago, Marauder said:

Let's race! Stinky Pants never took me up on it. I did have one race with a 68 F. He left an airport 6 minutes before I did. I caught him about 10 miles from our home airport which was about 70 nm away.

 

 

You're likely faster but I'll take the bet. Loser buy 's lunch!  We should do a time to climb as well.   I had a race like yours with a pristine Comanche 180 except I caught him inside of 10 mins of departure.

Edited July 10, 2018 by Shadrach

[Guest]

2 hours ago, Shadrach said:

You're likely faster but I'll take the bet. Loser buy 's lunch!  We should do a time to climb as well.   I had a race like yours with a pristine Comanche 180 except I caught him inside of 10 mins of departure.

To defend the honour of the Comanche and Piper line up, I may take up the challenge,  I will leave the gear down to make it more sporting!

Clarence

[jaylw314]

19 hours ago, Shadrach said:

. What’s odd about the chart is that it depicts thes abusive power settings. Leaning to best power at those settings is an obvious no no. 15.8GPH translates to 50ROP at 200hp and whatever MP is needed to support it. 

I'm guessing that chart was intended by Lycoming to be a theoretical depiction, not a suggestion of how to run your engine!

OTOH, somewhere out there there is a test run of an IO-360 at full power on a stand leaned to best power.  The IO-360 essentially produced no detonation even at the highest CHT of 495 degF!  Not that that's a great idea, but it gives some reassurance as to the kind of detonation margin we have...

Ha, found it!

[ArtVandelay]

OTOH, somewhere out there there is a test run of an IO-360 at full power on a stand leaned to best power.  The IO-360 essentially produced no detonation even at the highest CHT of 495 degF!  Not that that's a great idea, but it gives some reassurance as to the kind of detonation margin we have...
Ha, found it!

Notice the timing is 20° FWIW.

[DualRatedFlyer]

34 minutes ago, jaylw314 said:

I'm guessing that chart was intended by Lycoming to be a theoretical depiction, not a suggestion of how to run your engine!

OTOH, somewhere out there there is a test run of an IO-360 at full power on a stand leaned to best power.  The IO-360 essentially produced no detonation even at the highest CHT of 495 degF!  Not that that's a great idea, but it gives some reassurance as to the kind of detonation margin we have...

Ha, found it!

..... Quickly compares engine serial number on graph to serial number in logbook...

 

[Shadrach]

1 hour ago, M20Doc said:

To defend the honour of the Comanche and Piper line up, I may take up the challenge,  I will leave the gear down to make it more sporting!

Clarence

Didnt know you had a PA24-180! 

[Guest]

44 minutes ago, Shadrach said:

Didnt know you had a PA24-180! 

At some point as I open the throttle it is a PA24-180.

Clarence

[Marauder]

To defend the honour of the Comanche and Piper line up, I may take up the challenge,  I will leave the gear down to make it more sporting!
Clarence

How about you leave half of your jugs at home?


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[Shadrach]

1 hour ago, Marauder said:

 

How about you leave half of your jugs at home?


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I’m betting you get that line more often than Clarence!