Ignition timing VS engine wear

[Norcalrv7]

I have been pondering the effects of ignition timing lately. I know the focus is usually on how much advance can be run safely, but I am curious about possible downfalls of not enough timing.

Reduced timing leads to higher EGT numbers

Could this lead to increased exhaust valve temperature/wear?

Caleb

[N941WR]

Advancing timing doesn't always improve performance. Setting the correct timing for conditions is the key to good performance.

[rv6ejguy]

Running timing with mags at the data plate 22-25 BTDC doesn't affect life long term.

Doesn't seem like any good reason with EIs to run less than this.

[DanH]

Originally Posted by Norcalrv7

Reduced timing leads to higher EGT numbers

How much higher?

[Toobuilder]

Originally Posted by rv6ejguy

Running timing with mags at the data plate 22-25 BTDC doesn't affect life long term.

Doesn't seem like any good reason with EIs to run less than this.

Well, unless you think that the fixed timing on a magneto is a compromise between detonation protection at TO power and efficient ops at high altitude. If that is the case, then the data plate value is likely as far advanced as they can go and still retain an acceptable detonation margin, and some retard would actually help.

I've showed how flat the curve is at 100% power through flight test. However I was looking for an increase in speed as I advanced from well below data plate value to well above - I wish I followed up that test with retarding timing until I saw the speed fall off. That would have established the back end of the range.

[Toobuilder]

Originally Posted by DanH

How much higher?

And what is the factory's EGT limit for continuous ops with a NA Lycoming?

[rv6ejguy]

I think data plate timing would have to be set to avoid detonation at SL WOT and the rest is a compromise. Someone is gonna do it for an extended period, so you need to protect against the worst case scenario.

[Toobuilder]

Fortunately, I have an engine management system that allows in situ test!

[Norcalrv7]

EGT#'s don't go up a whole lot with retarded timing but the # is a short glimpse of what is going on the rest of the time in the cylinder.
I have heard the old wives tale about retarded timing burning exhaust valves in car engines.

Other OWT's I've heard is that retarded timing can cause a higher load on the coolant system,which would be contrary to Nigel's recent article in Kitplanes.

I guess the scenario I am thinking of would be as Ross pointed out, that data plate timing values are set for full power, with everywhere else in the lower ranges being a compromise (not enough timing). I'll stop beating around the bush and ask if we will possibly see less exhaust valve problems in the long term with an "optimized" ignition curve.

Caleb

[DanH]

Originally Posted by Norcalrv7

EGT#'s don't go up a whole lot with retarded timing but the # is a short glimpse of what is going on the rest of the time in the cylinder.

Here's EGT and valve temperature plotted together. Looks like some small change in EGT just means a small change in valve temperature. To your original question, I doubt a small EGT increase will have any significant effect on life, probably less than the guy who lets his CHT run hot.

I have heard the old wives tale about retarded timing burning exhaust valves in car engines.
Other OWT's I've heard is that retarded timing can cause a higher load on the coolant system,which would be contrary to Nigel's recent article in Kitplanes.

That's why they call them OWT's.

I guess the scenario I am thinking of would be as Ross pointed out, that data plate timing values are set for full power, with everywhere else in the lower ranges being a compromise (not enough timing).

I'll go with Mike's view; fixed timing is a balance between max power and enough advance for partial power.

If timing was set entirely for engine protection at full power, it would be much more retarded, so you could put the mixture knob anywhere you want at SL WOT. With our standard timing, you dare not lean anywhere near peak at WOT, at least not on a hot day with high CHT...there be dragons.

Now consider Nigel's work. It took very little extra advance to find peak power when running best power mixture.