What kind of fuel flows do you guys see at full power for take off 300hp? and 24 square.

My 185 previously put out 25 GPH at full power at sea level. Now it makes 30.

Don't know what my full rich mixture at 24 squared is but I could check next time.

Squash wrote:My 185 previously put out 25 GPH at full power at sea level. Now it makes 30.

What happened?

It got turned up.

Squash wrote:It got turned up.

That sounds kinda high. You have the naturally aspirated IO-520, right? Is it a cold temp compensation thing?

I'm thinking 30 more cubic inches happened

Keeping the t/o fuel flow around the redline on the 520 and 550 will help preserve your cylinders. CMI does not publish the fuel flows that high because they need to meet spec as far as HP goes.

Between 22 to 24 gph depending on Sea Level or traveling around the mountains. Take off at 2850 RPM.

I don't do much 24 squared, but 17 gph seems about right. My most common setting is 2400/22" leaned 100 ROP, yields 16 gph and 162 MPH at ~5000'.

Bill

You want to see OVER 25 gph on a calibrated guage. As noted by behindpropellers, running the fuel flows high at takeoff power really helps cool your cylinders and improve their life. All the 185/206s I flew we had the fuel flows turned up higher than factory spec for this reason.

On the 550 engines, that fuel flow on takeoff should be in excess of 30 gph.

MTV

Here is a nice article:

http://www.avweb.com/news/savvyaviator/SavvyAviator_65_WhatsYourFuelFlowAtTakeoff-199805-1.html

I think John Deakin, of Advanced Pilot Seminars, has a similar article but I can't find it.

Summary:

"I think one of the biggest factors contributing to early cylinder demise is inadequate fuel flow at takeoff. These engines require a very, very rich mixture to avoid excessive combustion temperatures and pressures at full takeoff power." "Fuel flow at takeoff is like tire pressure: too much is better than too little. A little excess fuel flow on takeoff might reduce takeoff power by a couple of percent, but a little shortfall can overstress the engine and fry the exhaust valves in short order. I'd much rather see takeoff fuel flow a tad over red-line than significantly below it." "The "gold standard" for adjusting fuel flow on fuel-injected TCM engines is a 39-page service bulletin called SID97-3E." "If you don't have your copy of SID97-3E handy, here's a quick rule-of-thumb you can use:

For a normally aspirated fuel injected engine designed to run on 100-octane fuel (8.5-to-1 compression ratio), takeoff power fuel flow in GPH should be roughly 9% of the engine's maximum rated horsepower. (For example, an IO-520 rated at 285 horsepower should flow about 25 to 26 GPH.)"

The link in his article is broken, but you can find the SID here: http://bonanza.org/documents/SID97-3E.pdf

The IO-520D at 2850RPM should be at 26.1gph, according to the document.

Edit:
At 24 squared I lean back to 12.5gph, but I usually run way oversquare and dial back to 11.5gph at the same MPH.

NZMaule wrote:I'm thinking 30 more cubic inches happened

Ha ha. No. I wish.

Early on, I was running my IO-520 and my O-360 with factory fuel flows. On takeoff, my temps were just high... like CHTs of 425. Baffles were good. This is with both planes.

Then I discussed with a few people and researched the issue. I ran across some engine data that suggested flows in the 10% of takeoff HP could keep you nice and cool.

So, for the 185, that was 30 gph. In the Husky, that was 18 gph.

Guess what? CHT's in both planes are amazingly better. And I have the red knob that I can pull back to whatever I want if needed since I do lose a bit of power being richer. I rarely need to lean to squeak out the power, but it's there if I want it. If you start out too lean, you don't have the option to go richer when your CHT's are climbing into the bad zone.

Thanks guys. My friend just bought a 185 and the numbers he was being told did not seem to make sense. I will get him to make sure the fuel flow monitor is properly calibrated first. To me 300hp uses 30gph was the basic rule.
KenW

mtv wrote:You want to see OVER 25 gph on a calibrated guage. As noted by behindpropellers, running the fuel flows high at takeoff power really helps cool your cylinders and improve their life. All the 185/206s I flew we had the fuel flows turned up higher than factory spec for this reason.

On the 550 engines, that fuel flow on takeoff should be in excess of 30 gph.

MTV

WHAT MTV SAID!!! A 520 should be 28 gph or better.

My two cents,
gunny

I am a new 185 owner and was very interested in that too.
I have been told that the fuel flow gauge in there airplanes is not all that accurate as its not an actual fuel flow gauge but a fuel pressure gauge calibrated in FF. A full engine monitor is a must and just bought a JPI FF gauge to compliment the JPI monitor in the plane. It was on sale at Chief a short while ago for $100 off so I couldn't pass it up.
As far as the 24 square goes I initially used the recommendation from the Cessna 185 manual as a guide which is 14.6@5000'. In using the JPI monitor and running 75 rich of peak the fuel flow was 15.2 as indicated on the Cessna gauge. The plane is scheduled to go in the shop in a few days to have the JPI FF installed so will have a much better idea on what the actual FF is.
My engine came with factory balanced injectors so will be running LOP once I get more comfortable in it.
Just my 2 cents worth.
Tom