Fuel flow during take-off IO-360

[cnoe]

For you motorheads... what do you consider to be the best injection system setting for fuel-flow during take-off (sea level) on the IO-360?

Busch quotes a close rule-of-thumb setting as 9% of rated HP on a normally aspirated engine which would be 18.0 gph in my J. He states that you should err on the side of too-rich at the risk of losing a bit of power as opposed to being too-lean at the risk of excessive cylinder temps.

Mine is flowing at 19.0 - 19.1 and the temps look good but I'm concerned that I may be a bit too rich. I get significantly less RPM drop during the mag-check at run-up if I lean a bit first (which increases my RPMs with a static throttle setting).

It's not a big problem but it gives me a warm fuzzy feeling seeing less mag-drop. Still it's a pain in the rear to "lean" during the run-up. Maybe I should just accept the ~125 RPM drop at full rich as perfectly fine. (Note: My primary focus on run-up is seeing the rise and fall of EGTs on the JPI.)

Any thoughts?

[MB65E]

Well unfortunately, It's not adjustable in the field unlike the continental. Best bet is to have the overhaul shop bench test it. They should have all the right set up Equiptment. You could lean it out manually with the mixture knob if you wanted. 

-Matt

[ArtVandelay]

I peek out at 18.3,
I start to lean around 2000', and go with sum of 18 rule keeps me safely in the ROP. So for 3K ft, my target FF is 15 gph.

[cnoe]

I don't think it's ready for bench testing yet as my take-off performance is fine. I'm not interested in leaning for take-off either. My FF is calibrated extremely accurately so it's truly flowing right at 19 which I believe to be well within an acceptable range. It just bugs me that it's not "perfect". I think I'd feel better if it were 18.1 - 18.5 but is otherwise just me nit-picking. Still I'm curious what others are seeing (and believe). FWIW my servo was OH'd 8 years ago.

I'll lean in the climb to maintain T/O EGT on my hottest cylinder which keeps me about 220 ROP. I hadn't heard the "sum of 18" rule but that seems reasonable; thanks for sharing.

[carusoam]

There is a document for your plane that specifies FF at SL and Full throttle...

It is possible, that your mechanic can set it to the wrong spec at annual.

For the 310hp IO550, FF is up around 29gph at FT and 2700rpm.

For the 280hp IO550, FF is around 25gph at FT and 2500rpm.

Need to check the design document (TCDS) for the M20 airframe and any STC that may apply.

The rule of thumb probably works, but MSers tend to read more to get more.

Best regards,

-a-

Note: FFs in this post are suspect, they are based on fuzzy memory.  The STC for the IO550 gives FF in Lbs/hr.  Consulting with the STC writer is always a good idea...

[wishboneash]

Mine is closer to 18.5. I posted a while ago the exact numbers. But close enough.