Twin Spark paper

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Martin Benade
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Re: Twin Spark paper

#16 Post by Martin Benade »

Well, diesel is compression ignition. Zero plugs. The paper mentioned in the first post mentioned cng I think
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Ron LaDow
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Re: Twin Spark paper

#17 Post by Ron LaDow »

In case is wasn't obvious from my earlier post, the intent of the extra plug is to reduce required ignition advance, with the resultant flame travel distance and time, in those chambers which would benefit by that approach; notably NOT modern chambers with a central plug.
If so, the engine benefits from the reduced ignition advance in two ways: 1) The burn spends less time pushing the piston the 'wrong' way BTDC, and, 2) A shorter ignition lead allows a higher CR before onset of detonation.
The concern here is the notably ugly 616 chamber with the flame travel required to get to the 'attic' over there at the intake valve black-hole from the plug way over here. Sticking a piston with a large dome in can make it worse, but regardless, it is a geometry rejected by RR during the Merlin development as 'subject to detonation' (The 'Ramp Chamber' "Allied Aircraft Piston Engines", Graham White, Pg 48).
So some data is appropriate:
On a series of dyno pulls on a notably 'stingy' dyno (Alan's dyno at the former Stable), 1720cc, 266* cam, stock muffler, engine dyno (no BS 'estimated' losses), we found:
Zenith 32mm carbs, 32* advance, 9.5:1CR - 83.32HP @ 5K RPM, 89.15#/ft @ 4.5K RPM
Zenith 36mm carbs (CNC manifolds), 32* advance, 9.5:1CR - 91.96HP @ 5K RPM, 97.20#/ft @ 3.5K RPM
Zenith 36mm carbs (CNC manifolds), second plug, 25* advance, 10:1 CR - 106.65HP @ 5K RPM. 102.03 #/ft @ 4.8KRPM (100 #/ft @ 4K).
You can certainly argue that it is too expensive or difficult, or that the maintenance charges are too expensive (Jim, it ain't a Benz), but you cannot argue it has no benefit on the power output of a 616 engine.
I do not address Ford, Nissan or Alfa designs; I know nothing of the geometry. If someone has A-B data on those, please do post it.
Whether a second plug would help a lawn mower or not I will leave to the decision of straw-graspers.
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C J Murray
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Re: Twin Spark paper

#18 Post by C J Murray »

Ron LaDow wrote:On a series of dyno pulls on a notably 'stingy' dyno (Alan's dyno at the former Stable), 1720cc, 266* cam, stock muffler, engine dyno (no BS 'estimated' losses), we found:
Zenith 32mm carbs, 32* advance, 9.5:1CR - 83.32HP @ 5K RPM, 89.15#/ft @ 4.5K RPM
Zenith 36mm carbs (CNC manifolds), 32* advance, 9.5:1CR - 91.96HP @ 5K RPM, 97.20#/ft @ 3.5K RPM
Zenith 36mm carbs (CNC manifolds), second plug, 25* advance, 10:1 CR - 106.65HP @ 5K RPM. 102.03 #/ft @ 4.8KRPM (100 #/ft @ 4K).
How do you explain that the same single plug engine with larger carbs makes peak torque 1000rpm lower?

I'm not sure what the twin plug number really tells us because of the .5CR increase which also changes the shape of the piston. Was the intake closing point kept the same? Probably. Did you try the single plug with 10CR at an optimized ignition timing? Was the fuel used from run to run from the exact same batch? What octane?

Do you have graphs of these three pulls laid over top of each other?
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Jacques Lefriant
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Re: Twin Spark paper

#19 Post by Jacques Lefriant »

Hi
Porsche used twin plugs in the 4-Cam engines. the 2 valve Hemi was later used on the 911 but until the 3.6 (964/993 100+mm) twin plugs were only used on race cars 906 etc. even the 3.6 Turbos went back to single plug. This paper validates why Porsche employed the twin plug setup on the 911s.
j
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C J Murray
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Re: Twin Spark paper

#20 Post by C J Murray »

Jacques Lefriant wrote:Hi
Porsche used twin plugs in the 4-Cam
engines. the 2 valve Hemi was later used on the 911 but until the 3.6 (964/993) twin plugs were only used on race cars 906 etc. even the 3.6 Turbos went back to single plug. This paper validates why Porsche employed the twin plug setup on the 911s.
j
In other words Porsche used 2 plugs where they used high compression TALL pistons that effectively split each cylinder into 2 separate combustion chambers with 2 separate flame fronts. Street engines and turbos with low dome pistons derived no advantage from twin plugs.

A 356 has a low and flat piston. Even the 356 race pistons are not tall like a hemi race piston.
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Mike Wilson
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Re: Twin Spark paper

#21 Post by Mike Wilson »

I was thinking along the same lines, Cliff, in that different variables: configuration of combustion chamber and piston top, timing, compression ratio, etc. have an effect on horsepower and torque and using twin plugs does work when the variables are conducive to that goal. (Or am I full of that which eminates from the south end of a northbound bovine?! Ha!

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Ron LaDow
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Re: Twin Spark paper

#22 Post by Ron LaDow »

C J Murray wrote:How do you explain that the same single plug engine with larger carbs makes peak torque 1000rpm lower?
I haven't given that a lot of thought; possibly the cam favors better breathing at that that RPM? Dunno.
Cliff, I'm not about to ruin a friendship over your desire to find a twin-plug engine to be the spawn of Satan. I have no idea why you find it so, but it is quite obvious that you do.
I explained (above) my reasoning and then quoted the the results from my notes which seemed to support that reasoning; you might look again at the explanation; chamber geometry is not only the piston.
No, I do not have the data in the precise form you prefer. Those runs were done some 15 years ago and what I have now is my notes from the runs.
I stand by my comments.
For those of you who have other theories, I suggest you put some skin in the game and support your claims.
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Jacques Lefriant
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Re: Twin Spark paper

#23 Post by Jacques Lefriant »

Hi Ron
it can't hurt and for an airplane it may be the difference from crashing but there are easier ways to improve the combustion process in the 356/912 I believe the biggest bang for the buck would when buying pistons get asymmetrical ones that mirror each other per side.
j
 

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Alex Goodhart
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Re: Twin Spark paper

#24 Post by Alex Goodhart »

2005-01-19
ine are discussed.
Last edited by Alex Goodhart on Sat Oct 13, 2018 3:53 pm, edited 1 time in total.
 

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Jacques Lefriant
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Re: Twin Spark paper

#25 Post by Jacques Lefriant »

Hi Alex
my point is the 356/912 combustion chamber could be improved with less effort than going to twin plug. the easiest is to use a different piston design then you could address the head and yes you could improve a little more by going to twin plug.
j
 

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Alex Goodhart
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Re: Twin Spark paper

#26 Post by Alex Goodhart »

I agree
Last edited by Alex Goodhart on Sat Oct 13, 2018 3:53 pm, edited 1 time in total.
 

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Re: Twin Spark paper

#27 Post by C J Murray »

Hi Alex,
What were the differences in ignition advance curves between the single plug setup and the twin plug setup? I assume the full advance number was different but what timing was used between idle and full advance? Which twin plug distributor arrangement did you have on the 1883?
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Re: Twin Spark paper

#28 Post by Ernesto Cabrera »

The ideal location for the spark plugs in small bore gasoline engine is at the center of the combustion chamber. As valve seizes increased and combustion chambers got flatter, the space between the valves got smaller and necessitated moving the plug to one side, so, depending on piston and combustion chamber configuration, flame propagation became a problem, because mixture strength was not alway homogeneous on both sides of the chamber. This makes the case for the twin plug engine. In the case for the four cam Carrera engine, the valve seize was increased to the point they needed to have a deep combustion chamber. This required a big lump of a piston dome, which interfered with flame propagation and made nit necessary to have another plug on the other side of this big lump.
 

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Alex Goodhart
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Re: Twin

#29 Post by Alex Goodhart »

hgf
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GregVandenbussche
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Re: Twin Spark paper

#30 Post by GregVandenbussche »

Sorry late to the party:
I think when Jacques talk about different piston geometry he might be talking about something like this?
Cosworth piston HC
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