Hey guys! I’ve been doing everything to lower my CHT’s on my Continental IO-550 below 415°F

Yesterday my mechanic suggested retarding the ignition timing to 20 instead of 22

What do you guys think?
Are there any risks?


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Setting the magneto to engine timing to anything other than what is stamped on the data plate is ill advised. Are you certain the ignition timing is already set accurately?

I don’t think the TCDS or data plate specify that number as maximum advance. My O-320 has it listed as just “spark advance,” which in the certified world means that at Wide Open Throttle (WOT) the advance should be at this number (or, with a fixed-timing mag, it should *always* be at that number).

Reducing timing advance will move the cylinder’s peak pressure to later in the the piston stroke, which gives less time for that pressure to push on the piston/connecting rod/crankshaft. This results in less power but also less stress, which can help lower temperatures.

I can’t think of any negative impacts to reducing timing by 2° other than reducing power a smidge. Having said that, I don’t think that 2° will make a significant difference in temps, either.

If the engine is supposed to fire at 22°, I’d be much more interested in figuring out why we can’t keep it at a nominal temperature at 22°. Is it a standard installation? What’s different about your engine install from anyone else’s? How are your baffles? Fuel pressure/flow?

CamTom12 wrote:I don’t think the TCDS or data plate specify that number as maximum advance. My O-320 has it listed as just “spark advance,” which in the certified world means that at Wide Open Throttle (WOT) the advance should be at this number (or, with a fixed-timing mag, it should *always* be at that number).

Reducing timing advance will move the cylinder’s peak pressure to later in the the piston stroke, which gives less time for that pressure to push on the piston/connecting rod/crankshaft. This results in less power but also less stress, which can help lower temperatures.

I can’t think of any negative impacts to reducing timing by 2° other than reducing power a smidge. Having said that, I don’t think that 2° will make a significant difference in temps, either.

If the engine is supposed to fire at 22°, I’d be much more interested in figuring out why we can’t keep it at a nominal temperature at 22°. Is it a standard installation? What’s different about your engine install from anyone else’s? How are your baffles? Fuel pressure/flow?

Hmmm, that’s a good point, we shouldn’t have to retard the ignition to keep the temps lower.

Actually I feel like my Fuel Flow is a little low

Im getting 25.7gph at Full power
But mechanics say it’s enough




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NO, do not do this! See my post on the other thread you started.

Kurt

G44 wrote:NO, do not do this! See my post on the other thread you started.

Kurt

Thanks Kurt! Already read it.
I believe you are absolutely right


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25.7 is WAY too low for a 550 at full power.

But that pic isn’t at full power, it’s at 27”/2500 rpm. What is the fuel flow at wide open throttle and 2700 rpm?

The number one culprit for a hot running 520/550 (in climb) is fuel flow, or lack thereof. You should be at 29-30 gph, minimum. The numbers Continental provides are too low, plain and simple. Find someone who not only knows how to set up the fuel injection system (and has the proper gauges to do so), but is also willing to go a few gph above book numbers at full power.

I'm curious if there is any downside to bumping the full-power fuel flow up higher than the factory numbers?
Doesn't seem like there would be, but I don't know squat about setting up injected engines.

Cannon wrote:25.7 is WAY too low for a 550 at full power.

But that pic isn’t at full power, it’s at 27”/2500 rpm. What is the fuel flow at wide open throttle and 2700 rpm?

The number one culprit for a hot running 520/550 (in climb) is fuel flow, or lack thereof. You should be at 29-30 gph, minimum. The numbers Continental provides are too low, plain and simple. Find someone who not only knows how to set up the fuel injection system (and has the proper gauges to do so), but is also willing to go a few gph above book numbers at full power.

Agreed. Should be 2700 at full power not 2500.