Posted for "George Braly" <gwbraly@gami.com>:

Interesting.

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.

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.

Like maybe a range from 160 Hp to 155 or 157 Hp on a  320 sized engine.

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.

At lower power settings,  the engines are a bit more sensitive to
optimal timing to achieve  MBT, as compared to  full power operation. What do your EGTs run at full power on take off ?   At what fuel flow?

Regards,  George    _____   > > > I had a 400 hour Don George 1992 Cermichromed I/O 320 with 9:1 pistons
and a Hartzell carved (thickness tapers at the end), 70 inch constant
speed prop.  I replaced BOTH Slick mags with the LASAR system (O 320
Control Unit (CU)), all timed for 25* BTDC.  I immediately experienced
energetic takeoff runs, better climb rates and better performance ROP at
altitude.  The EGTs were about 70 degrees cooler than similar power
settings achieved with the old mags - The CHTs were 15 to 20 degrees
higher.  I have not retained data from that era.
 ...snip...