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frank.hinde(at)hp.com
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 Posted: Mon Mar 03, 2008 11:05 am Post subject: Ignition control in a dual alternator dual bus system |
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Eh?....I think you might be missing each others point...
First off, there is no loss of power/efficiency with a single EI and mag...there is a reduction of fuel burned and probably a small power increase if you go from a dual mag to a single EI/mag.
At low manifold pressure (high altitude) the advance will go beyond what a normal mag will do (which is fixed at 25 deg)...up to 40 deg or so of advance. This enables the thinned out mixture to make more power for a specific fuel consumption because it is lighting the fire earlier...as the thinned out mixture takes longer to burn this maximises the efficiency because max cylinder pressure is produced (hopefully) at the optimum point i.e 11 deg or so AFTER TDC
It is possible to run into problems (destructive detonation is one of the worst things) if the fuel octane is too low and the advance too great...
Anyway, yes if the advance is operating at 40 deg and the mag is fixed at 25 then it takes longer for the flame to spread across the cylinder which effectively retards the timing a little compared to if you have dual EI's...So for sure in terms of fuel economy adding a single EI gives the most benefit...adding a second gives a little more, but not as much as the first.
Best thing to do for starting/idling is to start on the EI for smoothest running/easiest starting.
Frank
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Deems Davis
Joined: 09 Jan 2006
Posts: 925
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| Posted: Mon Mar 03, 2008 5:03 pm Post subject: Ignition control in a dual alternator dual bus system |
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Noticed there's a lot of dialog about electronic ignitions. My engine
builder runs all of their engines on a fully instrumented dyno for 1 1/2
hours and records all of the data at 1 minute intervals as RPMs increase
to max. Their experience is that EI's show a decrease in HP as compared
to mags, in fact they will no longer build an engine with EI. Obviously
they can't simulate changes in altitude with their dyno set up. And the
actual results (at) altitude may be different, Thie was certainly
counterintuitive, but it is a data point that is worthy of
consideration, and is backed up with instrumented dyno runs. I was all
set to go with EI until I learned this and I've backed off to mags
until the emag/pmag 6 cyl version is out and has a LOT of experience
behind it.
I'm not trying to start an EI/MAG war here, and I'm certainly no
engine/electron expert, so don't shoot the messenger, I'm just trying to
share some additional information that seems the have a basis in fact
and experience.
Deems Davis # 406
'Its all done....Its just not put together'
http://deemsrv10.com/
William Slaughter wrote:
[quote]
Electronic ignition systems will not cause a loss of power at takeoff power
settings, as they advance the timing at lower manifold pressure cruise
conditions, just like the vacuum advance mechanism did in automobile
distributors of days gone by. Fixed magneto timing is set for the worst case
situation - WOT. The engine will run much more efficiently with the timing
advancing incrementally as the manifold pressure (and thus BMEP) declines.
William
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mlas(at)cox.net
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| Posted: Mon Mar 03, 2008 5:19 pm Post subject: Ignition control in a dual alternator dual bus system |
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Frank,
For the most part I agree. The points that I was trying to make were
small. The main reason for using EI (order not important) is to improve
the starting, overall HP, fuel specifics, and general smoother running
throughout the range of operation. I didn't want to confuse rated
operation to improved operation. The general point is, if your going to
run a mix of EI and MAG why bother, your not going to see much gain
unless you run both systems at the same timing point.
MIke
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mlas(at)cox.net
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| Posted: Mon Mar 03, 2008 5:42 pm Post subject: Ignition control in a dual alternator dual bus system |
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I can't speak for the Emag Pmag system, but we have Dyno data that shows
the opposite with the Light Speed systems on 6cyl engines. Depending on
power settings, data shows as much as 10% hp gain with high compression
pistons.
Mike
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