Timing advance Plasma III and SDS

I am automotive TECHNICIAN for past 20 years and I know very well automotive systems.
But after reading this manuals I am not sure what i am missing.
Need some explanation why this 2 companies have difference in base timing advance setup.


Plasma 3 manual Page 29 http://www.lightspeedengineering.com/Manuals/Plasma_CdiManual_20130317.pdf
- At idle the timing display should indicate 35? ? 2? when the manifold pressure
hose is connected and 16? ? 2? when disconnected.

SDS http://www.sdsefi.com/aircrafttuninglyc.htm
Typically, ignition timing starts out on most engines at about 10 degrees BTDC from 500 to 1000 rpm
The timing would stay at 25 degrees above this rpm all the way up to redline when you are operating on 100LL

As i see it Base ignition timing( before corrections)
Plasma 3---Idle BTDS 35* High RPM 16* BTDS (looks wrong to me)
SDS--------Idle BTDS 10* High RPM 25* BTDS

Thank you

Plasma

Hi,

The procedure you are referencing in the Plasma manual is to verify that the controller is responding to manifold pressure changes.

The range in normal operation with manifold pressure connected is ~35 degrees at idle to ~20 degrees at max power. 20 degrees is the fixed timing of mags and is generally the optimal setting for full power. This is assuming you have an engine with a compression ratio of 8.7:1 that is normally timed at 20 degrees.

My engine is 8.5:1 so it's 40 degrees at idle and 25 degrees at full power.

Can't speak to the SDS.

Craig

I cant believe I am alone having this question

I Understand this is test to check range But this test simulates
Full throttle and Idle MAP conditions
This means it is working same way during flight
High pressure = full throttle -> 16*
Low pressure = Idle -- > 35*


Can anyone give some explanation to this numbers????
why would you need 35* advance at idle???
and 16 * full power why not apposite????

>why would you need 35* advance at idle???
>and 16 * full power why not apposite????

I believe it has to do with the _load_ on the engine. Idle = low load and therefore more advance. Full power = high load and therefore less advance.

See if this works: the Lightspeed is designed to advance around 40 deg at low atmospheric pressure (high altitudes) where the air is thin and the charge burns slowly. At 15K feet, the atmos. pressure is 16.88". On the ground at idle with throttle closed, your MP is a roughly similar number (12" or so--I don't have a MP gauge) so the ignition advances thinking it's at high altitude. When you disconnect the MP line, it thinks it is back at SL and retards the advance.

I suppose SDS limits their advance to 25 deg because Lycomings are normally limited to 25 degrees