Oh boy I sure love getting opinions that diverge from the same starting
point and go 180 degrees!  Perhaps they who are knowledgeable with no
axes to grind would fill me in with details.  The situation involves
comparing/contrasting a TSIO550 with dual mags vs dual electronic
ignition.  The route that I chose was dual LSE, hoping that the variable
advance would give me higher power at cruise and better fuel efficiency,
and would eliminate mag failure with age or high altitude.


Today I spoke with an engine rebuilder who stated in his dyno testing
that an IO540 (factory rated at 315 hp and rebuilt for 340 hp) yielded
only 280 hp when run at 2700 rpm WOT.  They attributed that power loss
to the spark advance profile built into the LSE and so always recommend
dual Bendix mags to their customers.  I would assume that their test
numbers are valid for the specific engine tested that day, but in
general should users of dual LSE ignition expect to sacrifice such
power?  Have any builders swapped out and tested both configurations? 
Theoretical or theological arguments accepted.

Bob,

 

Balderdash!

 

Luckily, your plane won't be flying on the dyno. 

 

Assuming the operator/technician hooked the ignition up properly and timed it properly, note that retardation (minor) may occur at high MAP, such as above 23-24".  If high compression pistons (>8.7:1) are used, Klause's recommendation to retard the base timing must be adhered to.  However, I see that you are turbo (normalized?), thus lower compression pistons. The timing is only affected by rpm since you won't see a MAP drop until critical altitude is reached at WOT or the engine is brought back to lope or idle.  High RPM, high MAP won't be advancing the spark.  Maybe Klause wasn't aware of the changes that allegedly brought the engine to 340 HP? Maybe an IO is different than a TSIO?

 

Bendix mags are better than Slicks, but they are still mags with the limitation of tight plug gaps, lower spark energy, shorter spark duration, etc.  So, one must check the timing with an automotive timing light, gap the plugs properly (automotive iridium seems to be better), etc. The benefits of the electronic ignition will be reaped in flight. 

 

I like a shop that pushes mags and ignorantly claims electronic ignitions are not as good as the old fashioned "buggy whip" product they are used to promoting and installing.  Maybe the guy is still driving a Model T with the spark advance lever on the steering wheel?

 

Now is the time to prove yourself the experimenter that we all know you are.  You do have an experimental airplane, don't you?  Some adjustments may be required.

 

Perhaps you could give Klause a call and see if you can extract a plain English explanation about your concerns.  It is probably better if you speak German, but you can still wish him a Merry Christmas.