Interesting.

George,

 

You bet it's interesting.

 

Either my writing is too obtuse or opaque or I left something out.

 

You responded to my historical setup:

 

<<<<I suspect the reason you did not see improvement in performance after
the 9:1 pistons on the LASAR was because it was timing  much  to early,
and that was corrected during the subsequent magneto
replacement/shuffle.
>>>>>

 

I did see vast improvement on the original setup with 9:1 pistons.  After my engine was rebuilt (again with 9:1 pistons), there was a clear problem with the LASAR system which was identified after I installed the switch that enabled me to run mags only or EI only.  The new sensor mag could not be set properly, resulting in initial timing of 29* BTDC (should be 25*). Thus, any advancement by the LASAR was on top of that.  More recently, that sensor mag was replaced with another that could only be timed to 27* BTDC - still a little advanced before the EI adds its own - exactly why I am running the advance-conservative O-360 CU.  So, I agree with the technical commentary that too early timing can defeat the performance objective.

 

<<<<<<<At high power ... changing the spark timing over a  range of  plus/minus
3 or 4 degrees off of  Max Brake Torque (MBT) timing has remarkably
SMALL effects on Hp.  Almost unnoticeable to a pilot.
>>>>>>>>

 

I can buy that.  What about torque?  I remember that HP = (Torque x RPM)/5252, the reason that HP and Torque curves cross at 5252 RPM, something I hope to never see with my little engine that could.  After all, the constant speed prop sees torque for prop pitch management and the torque plot for 1 revolution of a 4 cylinder engine is rather torturous - especially the dip during compression.  Who knows what the "harmonic damper" does to the CS prop except that it is "better" because of reducing the impact of that dip.  Hmmm, I must remember to switch the GPS to Km for better accuracy.

 

Then:

 

<<<<<<This concept is almost universally mis-understood by engine builders.
For example,  most IO-520 and 550 TCM engines are OVER timed at full
power and would actually make a bit more Hp if the timing was retarded
slightly.
>>>>>>

 

Exactly.  That is what led to my comment about a timing compromise by the manufacturer.  This may be somewhat true for the 320 also.  One person has told me that the Lightspeed EI can be obtained with the ability to alter the timing and he has seen increased takeoff (full power) performance by slightly retarding the spark to something like 22* BTDC for that operation.

 

<<<<<At lower power settings,  the engines are a bit more sensitive to
optimal timing to achieve  MBT, as compared to  full power operation.
>>>>>

 

Yeah, right now I am just poking around in the dark since the timing maps are Unison "proprietary" information - as though someone would copy them.....

 

<<<<<What do your EGTs run at full power on take off ?   At what fuel flow?
>>>>>>

 

As I said in the post you are responding to, 1280-1290 and 15.4 gph.  Note that the fuel flow could be less than accurate.  After a long flight, the EPI totalizer will claim I used about 5% more fuel than that measured by those very accurate fill-up trucks (this includes same truck at the same airport on the same day).  Of course, that was not flown at WOT.  However, I will record more environmental data (Baro, Palt, OAT) when I collect this information next time, including WOT lo altitude runs with and w/o LASAR.

 

Thanks for keeping at this,

 

Scott Krueger