IO550-N Power Settings

[Little Dipper]

I'd like to ask those of you who are running with the same thing   What rpm and power settings do you favor cruising at?   I just completed upgrading my 1995 Ovation with a factory new 310 HP IO550-N and a new Hartzel Scimitar propeller and am still breaking it in.    

Norm

N995K

[Cruiser]

Norm,

We need more input. What do you want? 

.... to go fast?

.... to save on fuel?

.... ROP or LOP ?

.... climb? cruise? endurance? 

[Txbyker]

I find that 2450 is best rpm for my 310 IO-550 at 100 ROP it's typically 177 kts, 17.5 gph, 9000 ft.

Edited to add some various info.

Flight Speeds
LOP 8000 22.3 2400 13.1gph 171 kts
ROP 8000 22.5 2400 18.3gph 174 kts

ROP 9000 21.5 2500 17.7gph 177 kts
ROP 9000 21.5 2400 17.0gph 175 kts
LOP 9000 21.5 2400 12.7gph 169 kt

 

Russ

[M20S Driver]

At 9500 to 10500 feet, 2400 rpm, WOT, 15.5 gph @ 70 deg ROP.   The TAS is around 171-175 kts.

Just a Driver...

[gsengle]

Curious why you're all flying ROP?


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[StevenL757]

According to CMI, and Bob Minnis - a co-designer of the IO550 engine platform (formerly a VP at CMI), and prior STC holder for the 310BHP upgrade, the best RPM for takeoff and climb is 2700RPM.  For cruise at all flight levels, it is 2550RPM, hands-down.

The IO550's tuned induction design and balanced injectors (either CMI or GAMI) favor LOP operations above many other engine variants.  Probably best to avoid that specific topic for the purpose of answering Norm's question...

Rgds, Steve

[M20S Driver]

1 minute ago, gsengle said:

Curious why you're all flying ROP?


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I do a lot of short flights from KPAO to KTRK or KMCC and most of the time is spent on climbing.  I find EGT more stable in ROP mode.

I use LOP in hot summer days on longer flights with lower power settings  since the CHT will be significantly lower and the range will be longer.

[gsengle]

In my Ovation I can go LOP pretty much immediately upon leveling off with no temp issues, and I'm getting 175 at more like 13 gph. Thats a lot of fuel savings.


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[M20S Driver]

6 minutes ago, StevenL757 said:

According to CMI, and Bob Minnis - a co-designer of the IO550 engine platform (formerly a VP at CMI), and prior STC holder for the 310BHP upgrade, the best RPM for takeoff and climb is 2700RPM.  For cruise at all flight levels, it is 2550RPM, hands-down.

The IO550's tuned induction design and balanced injectors (either CMI or GAMI) favor LOP operations above many other engine variants.  Probably best to avoid that specific topic for the purpose of answering Norm's question...

Rgds, Steve

+1...   I talked to Bob multiple times before buying the STC and he said the same thing. He indicated that the io550 is optimized at 2500 rpm and you could push to 2550 rpm.  My flying at 2400 has more to do with the noise and vibration levels than protecting the engine.

I climb at 2700 for the first 2000 feet and then go to 2550 in climb for the same reason above.  Bob mentioned that you can fly at 2700 all the time but you will be wasting a lot of fuel...

[Robert C.]

9000 or 9500 or 8000 or 8500ft (10k+ if the winds favor that)

WOT

2550 rpm

50 LOP, 12.5 - 13.5 gph

[M20S Driver]

1 minute ago, Robert C. said:

9000 or 9500 or 8000 or 8500ft (10k+ if the winds favor that)

WOT

2550 rpm

50 LOP, 12.5 - 13.5 gph

TAS?

[Robert C.]

At those settings and altitudes I get between 172 and 175 kts, just like Greg

[Guest]

9 hours ago, Little Dipper said:

I'd like to ask those of you who are running with the same thing   What rpm and power settings do you favor cruising at?   I just completed upgrading my 1995 Ovation with a factory new 310 HP IO550-N and a new Hartzel Scimitar propeller and am still breaking it in.    

Norm

N995K

How did you end up with an IO-550-N in your Ovation?  It's supposed to have G engine.

Clarence

[StevenL757]

18 minutes ago, M20Doc said:

How did you end up with an IO-550-N in your Ovation?  It's supposed to have G engine.

Clarence

Correct, and all Ovation owners who have purchased the 310BHP STC have the option to replace the "G" engine with an "N" (IO550-N8B or an IO550-N16B depending on whether you have air conditioning).  Part-for-part, they are nearly equal, save for a few small tweaks to the "N" (tapered cylinder barrels, among a couple others).  The "N" is actually rated to about 335-340BHP "out of the box" but derated to 310 (according to Bob M. - slightly more than a "G" with the 310 STC applied).

Shortly after buying the airplane in 2006, I was already planning to go to 310BHP eventually, so when overhaul decision time came around, matching the 310 STC up with the Acclaim Type-S prop STC (model F7498 - also a Bob Minnis STC at the time) and opting to have an "N" engine installed "native" out-of-the-box made sense.  The cost between the factory-rebuilt "G" and "N" was, literally, $14.

[Jeff_S]

Climb at 2700 RPM until 1000' AGL, then 2600 RPM to desired cruise altitude. 

Cruise at 2500 if I'm bucking a headwind, 2450 if I've got a tailwind to save a bit of juice. 

Never touch the throttle until descent and landing.

LOP in cruise, generally 12.5-13.5 GPH depending on altitude, air temps, etc. These settings always have me right around 175 KTAS, give or take.

Exceptions are loafing flights where I'm just soaking up some sun, or maintenance hops where I'm staying low to just get to a shop nearby, in which case I'll go 24/2400 or sometimes even 20/2400 but still LOP for any extended flight time.

[carusoam]

+ 1 for discussing with Bob Minnis. Take notes and ask questions.

+1 for 2700 and 2550 rpm selections.

+1 (N) engine. Slightly lower cost. Slightly lighter weight. Slightly more modern. Required slight adjustment of sheet metal to match shape of cylinders. Tach redline adjustment.

+1 TopProp.  Thin bladed aluminum Acclaim version.

+1 Factory reman.

 

Not mentioned...  break-in flights.  Max MP. Down low. RPM change every 15 minutes or so.  Following Continental's written procedure and oil guidance.  Use of a Mooney specific CFII to oversee the first few hours of break-in (mostly because I am not a skilled glider pilot)

Best regards,

-a-

[StevenL757]

Yep...forgot to mention the slightly lighter weight of the "N"...a bit more usable load.

[Txbyker]

It was -1 Celsius here the other morning and I could get about 29" on departure but I kept it at 27" instead of WOT.  It keeps my CHT's down considerably.  What do you guys do with manifold pressure in the climb up to cruise?

Russ

[StevenL757]

Leave it WOT all the way up...especially above 3000AGL.  Partial-throttle operation compromises efficiency in tuned-induction engines, and does not allow the engine to take advantage of available power.  Reducing MP in this scenario doesn't help the engine or "save it" in any way.

There should be little, if any, rise in CHT by adding the additional power you mention.  Given your OAT that day, you shouldn't be seeing any CHT values that even remotely give you cause for alarm.  If so, we probably need to have a different conversation.

Steve

[gsengle]

It was -1 Celsius here the other morning and I could get about 29" on departure but I kept it at 27" instead of WOT.  It keeps my CHT's down considerably.  What do you guys do with manifold pressure in the climb up to cruise?

Russ

Isn't there something else that happens with fuel flow at WOT, which is why you shouldn't back off on take off? Something with fuel flow? Accelerator pump?

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[Txbyker]

3 hours ago, StevenL757 said:

Leave it WOT all the way up...especially above 3000AGL.  Partial-throttle operation compromises efficiency in tuned-induction engines, and does not allow the engine to take advantage of available power.  Reducing MP in this scenario doesn't help the engine or "save it" in any way.

There should be little, if any, rise in CHT by adding the additional power you mention.  Given your OAT that day, you shouldn't be seeing any CHT values that even remotely give you cause for alarm.  If so, we probably need to have a different conversation.

Steve

Me and my CFI (Mark Johnson, MAPA proficiency instructor) experimented with this, this summer.  I do see about 15-20 CHT cooler by not powering so much manifold pressure on a normal day.  Is there a case that IO-550's can have excess MP at sea level, thus creating heat and no performance? Not meaning to create controversy, just education on my behalf.

Edit - according to the Continental manual it says to adjust power to maximum operating hp taking off.  According to the 310 STC max power at sea level, 59 degrees, 2700 rpm, is 24.4 MP.  So I guess my question is, does excess of 24.4 MP create unwanted heat and pressure or are you supposed to take off always WOT regardless of MP value?

Thanks,

Russ

[carusoam]

The fuel pump is on at WOT.

Not sure what turns it on, or off or what mode it is operating in Hi or low Boost.

Temps down low can significantly increase MP.  If you see higher MP than book value this is a decision you may want to make...  Since the IO550 was designed at power levels much higher than 310hp, it is a tough decision without much to go on...  ICP, cold cylinders, and initial T/O run.  Great question for Mr. Minnis...

Climbing out, I am using the blue box EGT method, (white box if you have the G1000.

What FF do you see during the T/O run..?

Best regards,

-a-

[Little Dipper]

21 hours ago, Cruiser said:

Norm,

We need more input. What do you want? 

.... to go fast?

.... to save on fuel?

.... ROP or LOP ?

.... climb? cruise? endurance? 

A moderate fast cruise without punishing the engine.

[GeorgePerry]

On 12/23/2016 at 0:31 PM, Little Dipper said:

I'd like to ask those of you who are running with the same thing   What rpm and power settings do you favor cruising at?   I just completed upgrading my 1995 Ovation with a factory new 310 HP IO550-N and a new Hartzel Scimitar propeller and am still breaking it in.    

Norm

N995K

22 in MP / 2400 RPM at 12.7 GPH 30-50 deg LOP.  I run this way 95% of the time.  Trues out about 170-173 depending on DA. About 10 knots slower than ROP but it saves about 3.5 GPH so it's worth it.