V12 Ignition Timing

[Draw-Tech]

Looking for Feedback

I'm debating to use single points, with a 12 point cam lobe or do I use double points and fire two cylinders at the same time with a 6 lobe cam, from what I read most 12 cylinder engines do that to balance itself.

Any comments ??

Draw-Tech

:wall:

 

[123RWO]

Points with a 12 lobe cam and a conventional coil won't allow very much dwell time which will limit max RPM. A far more sensible system would be to use a CD ignition which doesn't require significant dwell. I would forget the points and use a Hall effect distributor with the trigger magnets on the underside of the rotor driving a CD ignition box. It's simple to build, very reliable, and all the components are available and relatively cheap.

The most famous V-12 of all time, the Merlin, doesn't fire 2 cylinders at the same time. It does fire 2 plugs at the same time, but they are in the same cylinder. You can read about it's ignition system and also the firing order here: http://www.thunderboats.org/history/history0324.html

RWO

 

[Draw-Tech]

Thanks RWO

I will look into CD ignition, great reading on that site.

Draw-Tech

 

[gbritnell]

Hi Draw-Tech,
The first multi-cylinder engine I built had 4 cylinders. I wanted to keep the distributor fairly small and at that time there were no Hall type ignitions around so naturally I used a points setup and it worked fine. The next engine was a V-8 and I had the same goals for the ignition that I did for the 4 cylinder engine, small distributor and points. The distributor body was around 1.062 diameter. The engine would start and run but would not rev to any extent because I couldn't get enough dwell to charge the coil at higher rpm's. There was no way to make a bigger point cam without making the distributor very large so for a number of years the engine adorned my display case. When the Hall type ignitions came about I redesigned my distributor to use it. The diameter was still the same which made me happy and the performance was outstanding.
I would say that to use points for a 12 cylinder engine would be almost impossible without making a very large diameter distributor.
I would go with a Hall type but as with a point system you will still need enough dwell to charge the coil at higher rpms or the engine will just shut off. You could waste fire an extra cylinder and therefore only need 6 coil charges per revolution of the distributor, otherwise you're back to the large diameter.
gbritnell

 

[jwcnc1911]

George,

I've come to the conclusion that you are an engine Einstein. This isn't really helpful to me now as Stirling and Flame lickers are my fancy but it's incredible to see such knowledgeable people willing to help.

I see that you truly believe your tag line.

 

[mu38&Bg#]

CDI also have an RPM limit. Most will fire to something like 20,000 sparks per minute. So for a V12 this is 3400 RPM without waste spark.

Greg

 

[gbritnell]

Hi JW,
My engine knowledge base comes first from growing up in the late 50's and 60's when most every young man was into cars and hot rods. It was truly a wonderful time for the automobile lover, setting points, changing cams, milling heads etc. Don't get me wrong the cars today are engineering marvels but you just can't work on them, at least not at home.
The second part of my modeling background comes from the same time period. My father had brought me home a plastic model of an F-9-F Panther jet fighter. From that point I was hooked on models of all types and still build them today. When I was old enough to do odd jobs I bought a small used metal lathe. The only thing I recall making with it was chips as I had nobody to teach me how to use it properly. Later on I was lucky enough to have served an apprenticeship under some of the greatest craftsmen in the trade, metal patternmaking.
Combining the two aforementioned skill sets I am where I am today.
The shame is there are many fellows like me out there but they just aren't internet people. I have met so many great modelers and self taught engineers over the years that continually come up with new ideas for this hobby. I would love to mention them by name but it would really be unfair if I missed some so suffice to say that they're out there.
If you live anywhere near one of the great model engineering shows, NAMES, GEARS, The Black Hills show, Cabin Fever and a few others please try to attend and talk with the gentlemen there. Most of us are getting older and the knowledge base is dwindling.
gbritnell

 

[canadianhorsepower]

[QUOTE
I would go with a Hall type but as with a point system you will still need enough dwell to charge the coil at higher rpms or the engine will just shut off. You could waste fire an extra cylinder and therefore only need 6 coil charges per revolution of the distributor, otherwise you're back to the large diameter.
gbritnell[/QUOTE]

I totally agree with you on this one, must admit that hall type sure give an
other chance of keeping the stuff small

 

[Draw-Tech]

Hi all

Thanks for all the feedback, What is the best Hall Effect unit to use. As this engine is a bit larger my distributor diameter is about 2.25" the dwell angel is approx. 30 Deg.

gbitnell, you sound a lot like me, my father also was a machinist, Mechanical, chemical, electronic engineer all combined in one. When I was 9
years old, I can remember standing on a milk crate to reach the controls of fathers 9" lathe (which I still Have) All I have learned is through hard knocks I'm now 65 years old, and still have the urge to turn those cranks on my lathe, and milling machine. I have found that practical experience is the best teacher. What I know about engines was learned by owning a small engine repair shop from 1977-1987

We never stop learning!

Draw-Tech
Jack

View attachment Distributor_V12.pdf

 

[canadianhorsepower]

[QUOTE What is the best Hall Effect unit to use [/QUOTE]

do you mean Hall parts number or a ignition system

 

[123RWO]

See: http://www.cncengines.com/ic.html for the electronics package used in the Hodgson 9 cylinder radial. It will work in a 12 cylinder as well. The Hodgson distributor is about 1.81" in dia., so a 12 cylinder version would be somewhat larger. Remember that voltage does not scale so a certain minimum spacing for the distributor sparkplug terminals must be maintained.

The CNC CD box gives 12,000 sparks/min. which means 2000 RPM for a 12 cylinder. You could go to 2-6 cylinder systems to get 4000 RPM if need be.

There may be a faster CD box out there somewhere, but I don't know about it.

RWO

 

[Draw-Tech]

Great site RWO

Would I mount 12 magnets in the rotor of the distributor? I'm not trying to beat a RPM record, so this should be fine.

Jack Draw-Tech

 

[123RWO]

Yes, the standard design for the Hall effect distributor mounts the trigger magnets on the underside of the rotor where they pass by close to the Hall sensor as the rotor rotates. As each magnet triggers the sensor, the CD box generates a high voltage pulse that is wired back to the distributor center electrode in the standard manner. This design provides no built in ignition advance, so either advance must be programmed into the CD box or the distributor can be physically rotated a few degrees (usually by the throttle linkage) as needed.

RWO

 

[gbritnell]

Draw-Tech
You could mount 12 magnets and yes they would trigger the Hall sensor but the question I have is why do it that way? You say you wouldn't be concerned about getting high rpm out of the engine but by going to a trigger wheel and one magnet you could control the dwell time and in the process simplify the whole setup and as a side benefit gain whatever rpm the engine is capable of.
gbritnell

 

[gbritnell]

If you go to the Jerry Howell website, http://www.jerry-howell.com/IgnitionModules.html and read the paragraph on dwell angle about halfway down the page the late Mr. Howell explains the formula for calculating dwell angles. This will give you an idea of what he considers the proper amount of magnetic flux for charging the coil. He also states that he has never needed more than 1 magnet for his ignitions but this is based on using the diameter magnet that he spells out. Small engines operate just like their larger brothers, fuel, compression and spark makes them run. The problem is each engine is unique and once someone gets their creation running with any success they generally don't pull it apart to adjust the compression ratio, cam timing, carburetor sizing, etc., etc. to see if they can get it running better so there are no definitive charts from which to go by. Sticking to the topic, ignition systems, most everyone I know in this hobby uses a Hall type system today. It's so much simpler and generally reliable than points.
I would say that just building a twelve cylinder engine will be a daunting task so I wouldn't worry too much about the ignition at this point. I would say that getting the fuel mixture to the cylinders is going to be quite an experiment in itself.
gbritnell

 

[Draw-Tech]

Awesome gbritnell

I'm going to order one today, super price. I plan on using two of my carburetors that I designed for my 6 cylinder, Here is a model of my carb
go to autodesk.com download viewer free
Thanks for the great info

Jack

View attachment Carb.zip