REFLECTOR: Exhaust systems

[John Dibble]

I see the same big drop only it is REVERSED.  I get the big drop when I turn the mag off, so I
question the EI.  However I just read in the Franklin manual that the mag/EI should be tested
ONLY at 1100-1200 rpm and at 2300-2400 rpm as other speeds will result in large drops.  So I
will check this out.
My EGT increases with either the mag of EI off.  This seems logical since the combustion will
be less complete during the power stroke and more will occur in the exhaust cycle.
My Rose EI has some "smarts", but not as much as you suggest.  It simply adjusts timing
depending on both rpm and map (higher rpm=more advance, lower map=more advance).  The maximum
advance is supposed to be 28 degrees which is where the mag runs all the time except for
starting.
The EI is supposed to be better because it gives a stronger spark of longer duration.  To take
full advantage of this I understand that the plug gap should be increased to .028, but I
haven't figured out how to do that yet because the available tools gap to about .018 only.
That's all I know so far.....
My mag/EI toggle switches must be pulled out before they can be moved to protect from
accidental bumping.

John

steve wrote:

> Hi John,
>
> This is very interesting......
>
> Question: You are at the run up bay, set RPM to xxxrpm ready to do a mag check.
> You turn off one mag (or EI). The RPM drops by some value (50-100rpm??)What
> happens to your EGT ???  Does it;
>
> a) stay the same
>
> b) Decrease to reflect the small loss of power (rpm drop)
>
> c) Increase
>
> I thought the answer would be b) but guess what, the correct answer is c).
>
> I have asked many, some apparent 'experts' but have never had a satisfactory
> answer to why this is so.
>
> I can understand (I think) why the EGT increases when you switch the mag OFF and
> run on only the EI. We know that the egt will increase when you are on a single
> spark plug firing as outlined above. Now take into consideration that the EI has
> some 'smarts' and can both detect the power drop when you turn off the mag and
> can adjust the timing to try to recover some lost power.  This adjusting of the
> timing probably accounts for the extra difference you see when running on the EI
> only as compared to the mag only. Just don't ask me to explain it..... case I
> don't know. Maybe its simply that the EI is more *efficient**.
>
> More EI ramblings (sorry).....
>
>  The EI's are advertised as 'More power from your engine' or 'Saves you fuel'
> and to a degree this is true ... you will produce more power with EI than mags
> for a certain fuel flow or, you can power back a bit to duplicate the
> performance you saw using Mags and of course you are now using less fuel (cause
> you powered back).
>
> Light Speed EI claim as much as 10% fuel saving if you switch out 2 mags for a
> dual EI. Some round the worlders back up this claim. All of this goes to prove
> that EI allow the engine to be more *efficient*  (we knew that already).
>
> I have 1 EI and 1 mag on my Franklin Velocity, I can guarantee that most people
> are amazed at the different 'mag drops' I get during run ups .... turn the mag
> off....small rpm drop (about 30-50 rpm)  ....turn the EI off Huge rpm drop
> 250-300 rpm !!  used to be concerned that the mag was faulty, replaced it with
> the other new mag, timed it ..... no difference!   On an early test flight
> climbed to 2000' after T/O in moderate turbulence (bouncing around) suddenly
> felt/heard power loss guessed about 20% ....... noticed all 6 egt's rising
> significantly, must be something serious..... pucker factor also on the rise,
> decided to get down asap ..... uneventful landing..... long story short, I had
> knocked the overhead switch panel with my headset in all the bumping around
> whilst leaning forward to check for other traffic and knocked the EI OFF !!!!
> something to be aware of EI or Mags (unless you have a key type
> ignition/starter).
>