REFLECTOR: Exhaust systems

[Scott Derrick]

If the EI is operating normally your EGT's should remain almost the same 
operating on the EI alone, and EGT's should increase operating on the 
MAG alone.

Something is fishy here.  EI mistimed maybe?

Scott

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).
> 
> 
> Thursday, July 10, 2003, 1:51:21 AM, you wrote:
> 
> JD> Don't know.  That's a good point.  I'll check the next time I fly.  Is
> JD> your question for both mag and EI, or each separately?  Compared to
> JD> both, the EGT is higher with either the mag or the EI (highest with EI)
> JD> and the CHT is about 20 degrees lower with either one.
> 
> JD> John
> 
> JD> Scott Derrick wrote:
> 
> 
>>>Are you LOP or ROP?
>>>
>>>Scott
>>>
>>>John Dibble wrote:
>>>
>>>>At 2300 rpm/22" map, my EGT is 30 degrees higher on EI compared to the mag.  I'm
>>>>thinking that the EI timing needs to be advanced.  However the current EI "settings"
>>>>are already 4-5 degrees advanced beyond the 28 degrees specified for the Franklin
>>>>engine.  If I adjust the EI "settings" to 28 degrees, it's much rougher and backfires
>>>>on EI during run-up.  Any thoughts about using EGT/CHT to fine tune the timing?
>>>>
>>>>John
>>>>
>>>
> 
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> 
>