High CHTs and magneto timing

[snopercod]

So how close in timing do the two mags need to be? Mine are currently 1-1/2 degree different. Is that a problem? The engine is running fine.

[lr172]

Originally Posted by snopercod

So how close in timing do the two mags need to be? Mine are currently 1-1/2 degree different. Is that a problem? The engine is running fine.

no problem. I have one mag at 25* and an EI that ranges from 23 to 35* of advance, depending upon MAP. What you are looking to optimize or set is the total effective timing, which comes from the combination of the two sparks. You have two flame fronts and what we care about is where peak combustion pressure occurs relative to TDC.

Larry

[jrs14855]

Clearly the way the OP posted his question the mags timing is RETARDED, IE both mags are firing quite late. Late enough so the engine is likely low on power.
I have an 0 320 with 10-1 pistons. I was faced with breaking it in in very high ambient temperatures. One of the most respected engine builders in the US recommended mag timing of 22 degrees for the break in. This worked extremely well. It did not cause any significant loss of power.
Further there are some angle valve 360's that require the timing at 22 degrees.
Timing of 27 degrees will likely cause a higher CHT but is unlikely to cause any damage, especially on a stock engine.
PLLEASE do not bring EGT into this discussion. It is totally meaningless in this discussion.
The last check after resetting timing is to turn the prop backwards a few degrees past the timing mark and then slowly tap the prop forward until the timing light comes on.

[snopercod]

Originally Posted by lr172

no problem. I have one mag at 25* and an EI that ranges from 23 to 35* of advance, depending upon MAP. What you are looking to optimize or set is the total effective timing, which comes from the combination of the two sparks. You have two flame fronts and what we care about is where peak combustion pressure occurs relative to TDC.

Thanks, Larry. Tomorrow I'm going to try and get them both to 23 degrees, but won't obsess over it.

[RV7ForMe]

Originally Posted by jrs14855

One of the most respected engine builders in the US recommended mag timing of 22 degrees for the break in. This worked extremely well. It did not cause any significant loss of power.

Great you bring this up. I had been asking myself this because we also have a new stock engine that is running very hot.

WHY don't we use this as a standard to break in period as we know that they will hotter than normal especially in the RV cowl? what is the drawback? Wouldn't this give us a bit of a margin to get through the initial break in?

[DanH]

Originally Posted by RV7ForMe

Great you bring this up. I had been asking myself this because we also have a new stock engine that is running very hot.

WHY don't we use this as a standard to break in period as we know that they will hotter than normal especially in the RV cowl? what is the drawback? Wouldn't this give us a bit of a margin to get through the initial break in?

There is no drawback for the break-in application. You will see lower CHT and increased EGT. Do not be concerned about the EGT increase. It is just an artifact of slightly higher pressure at valve opening:

http://www.vansairforce.com/communit...2&postcount=29

[RV7ForMe]

Originally Posted by DanH

There is no drawback for the break-in application. You will see lower CHT and increased EGT. Do not be concerned about the EGT increase. It is just an artifact of slightly higher pressure at valve opening:

http://www.vansairforce.com/communit...2&postcount=29

Thanks Dan.