REFLECTOR: EI and Detonation

Sat Jun 23 08:30:55 CDT 2012

Sorry, I'll try to avoid the send key until finished.

On 6/23/2012 7:50 AM, John Dibble wrote:
> Mark,
>
> Don't know where to begin.  The problem is that over 900 hours, I 
> didn't know for sure I was detonating until I discovered one cylinder 
> liner and piston were eaten away at the top.  There were subtle hints, 
> like when the #5 cylinder temp increased by 50 C during descent from 
> 9500' with power near idle.  Going full rich brought the temp down.  
> Or when the #1 cylinder EI plug gap would become filled solid with a 
> dark material.  In the beginning I assumed that was carbon, but later 
> figured out it was metal, usually steel.  The real attention getter 
> was when the engine would stumble at 1000' right after T/O.  There's 
> more, but let's move on to the contributing factors.
>
> First of all my engine is a 10.5/1 compression Franklin.  I think the 
> high compression engines simply do not need (or can tolerate) as much 
> advance.
>
> Second, at the peak of detonation problems, I discovered the EI had a 
> bad ground ( 1 ohm of resistance) and I understand that a bad ground 
> will cause an EI to further advance by 10-20 degrees.  Now I check the 
> ground at every annual.
>
> Third,  there is no good way to verify that the EI is set up 
> properly.  It's like dead reconing, you set everything per the 
> instructions and assume that the timing is where it's supposed to be.  
> Well, mine wasn't.  I ended up retarding the timing by about 12 
> degrees from the instructions.  To preserve the 0 degree starting 
> capability, I retarded the timing by moving the timing ring rather 
> than an adjustment to the initial advance setting.  I determined the 
> desired timing by doing a "mag check" while flying, making several 
> adjustments on the gound until I achieved the same rpm drop with the 
> EI compared to the mag.  I have disabled the manifold pressure advance 
> function and use the minimum 6 degree rpm advance setting.  Perhaps I 
> could see some performance increase by using a little more advance at 
> high altitude, but for now I will keep it simple as avoiding 
> detonation is the prime consideration.  If I do decide to try more 
> advance in the future, I will install a rheostat and manually input 
> the extra advance, but it will be a guess as to how much, so I will 
> probably not try it.

John
>
> On 6/22/2012 10:48 PM, Mark Magee wrote:
>> Hi John,
>> Your issues with detonation are troubling me. I ran a Rose EI on a 
>> Long EZ years ago and know that at 11,500 I was 41DEG advanced with a 
>> reduced fuel burn of about 15%. We in the San Diego EZ squadron 
>> designed the advance curve and Rose burned it in.
>> How did you find out you were detonating?
>> Detonation could lead us back to our Glide Distance thread. I don't 
>> believe there are any working knock sensors out the for a LYC/CONT 
>> EI, yet it seems to me that retarding back to mag advance will kill 
>> the fuel savings advantage of an EI.
>> I'd appreciate any additional data on EI advance curve and detonation 
>> you've uncovered
>>
>> Mark B. Magee
>> N34 XL
>> Sent from IPhone 4
>>
>> On Jun 22, 2012, at 8:39 PM, John Dibble <aminetech at bluefrog.com 
>> <mailto:aminetech at bluefrog.com>> wrote:
>>
>>> Cruise altitude depends on the weather.  On a rare SKC day I fly 
>>> 9500/10500.  On a partly cloudy day, there are bound to be cloud 
>>> tops to 13000, requiring O2 if you want to stay above the cloud 
>>> bases where the air is far smoother.   When solid overcast, it's 
>>> usually smooth air below the ceiling.
>>> I'd go with the lesser advance timing, or even no advance at all 
>>> until you determine how much advance is right for your engine.  I 
>>> have one Rose EI on my Franklin and I had detonation damage from too 
>>> much advance.  I ended up disabling the advance and setting the EI 
>>> to the same advance as my mag.
>>>
>>> John
>>>
>>> On 6/22/2012 6:23 PM, Richard J. Gentil wrote:
>>>> I am planning on taking my first long trip in my Normally Aspirated, Dual EI, MT, IO-390, SERG. Going from Naples, FL to Norfolk, NE. (Day VFR. Not ready to test her in IFR yet.)
>>>>
>>>> I figure I can make it with one stop to stretch the legs and relieve the bladder.
>>>>
>>>> My question is cruising altitudes. (I can take an O2 bottle if there is any good gain by going up 16,500 or 17,500).
>>>>
>>>> What altitudes do you find most efficient etc for a Velo.
>>>>
>>>> I have two timing advance curves with my E-Mag and P-Mag. I am currently using curve A as set by the factory not tried curve B yet. (I have not hooked them up at an EICAD yet.)
>>>>
>>>>
>>>>
>>>> I would be very interested in your recommendations.
>>>>
>>>> Richard
>>>>
>>>> Sent from my iPhone 4 Classic
>>>>
>>>>
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