High CHTs

[s24789]

Did every trick we could find on the web, while waiting for ur friend Jim's plug tool to find exat position of TDC. Mags were way out. Should have been 25 BTDC but what we found was Left at 26 and right at almost 28. Adjusted and flew get flight with 30C at takeoff and WOT e highest was a short period of time at 400 then everything settled down to under 370. Ottom line is if you have hi CHTs fix the baffle leaks and accurately check e timing
Phelps

[RV10inOz]

Your post looks like some of mine when I use the iPad

Indeed, timing being set earlier than recommended does two things, and these are easy to spot, you will have a higher CHT and lower EGT than you would otherwise expect.

It also contrary to popular myth, does not produce more power!

[dlloyd3]

Advancing the timing (25 degrees) on my engine does appear to produce less power, higher CHTs. What would be the downside of 20 degrees? Rough running? More fuel burn?

[RV10inOz]

Changing the timing to 20 degrees would move the Theta PP further after TDC and this will show up with lower CHT, higher EGT(no big deal), and the resulting peak pressure will be lower (hence lower CHT) and torque would roll off.

There is a reason for the engine manufacturer nominating a timing point.

Low RPM performance would improve, but who flies around at 1200 RPM

Your observations are proving the theory and dyne tests are not illusions!

[N941WR]

Originally Posted by dlloyd3

Advancing the timing (25 degrees) on my engine does appear to produce less power, higher CHTs. What would be the downside of 20 degrees? Rough running? More fuel burn?

Dave,

Besides a change in power, you would see a drop in CHT and increase in EGT.

The reason is that the fuel air mixture is still burning when the valve opens so more of the flame goes out the exhaust and less energy is expanded in the cylinder.

Conversely, if you move the timing to say 28* BTC, your CHT?s will go up and your EGTs will drop. This is because you have more fuel/air burning in the cylinder and less burning in the exhaust pipe after the valve opens.

I recommend you set your timing to match what your engine manufacture recommends.

The results I mentioned above are for sea level conditions.

Up high, at reduced power, you can advance your timing without damaging your engine but you will see the same results with regard to CHT and EGT temperatures.

Give me a call, if you want to discuss this further.

[RV10inOz]

The reason is that the fuel air mixture is still burning when the valve opens so more of the flame goes out the exhaust and less energy is expanded in the cylinder.

Conversely, if you move the timing to say 28* BTC, your CHT?s will go up and your EGTs will drop. This is because you have more fuel/air burning in the cylinder and less burning in the exhaust pipe after the valve opens.

That is not quite accurate, however the intent is the same.

As suggested, set your timing at the correct place, there is nothing to be gained otherwise.

[RV8R999]

Originally Posted by RV10inOz

That is not quite accurate, however the intent is the same.

As suggested, set your timing at the correct place, there is nothing to be gained otherwise.

To get the more accurate answer I suppose we have to go to a APS seminar huh?

[RV10inOz]

No.... but it sure helps the understanding bit.

It can be found elsewhere. But it seems that a deeper understanding is not really appreciated, and in this instance it does not gain much.