What's the advantage???

More efficient combustion as there is no hidden corner of mixture from the spark. This allows you to run less advance and gives a sweeter time for the engine.
It would be more effective on hi comps than flat pistons as more opportunity exists for the spark to not find an easy way to all corners.
 
Grant said:
More efficient combustion as there is no hidden corner of mixture from the spark. This allows you to run less advance and gives a sweeter time for the engine.
It would be more effective on hi comps than flat pistons as more opportunity exists for the spark to not find an easy way to all corners.
Click to expand...


Isn't there something called swirl going on in the combustion chamber that has an effect on how the engine performs, if so, arn't more pointy things in there detrimental? Can you tell i'm not an engineer thingy!!
 
Not only beter combustion but more fuel can be used. Thne twin spark Alfas are fast but more to go wrong and thirsty.

Andy
 
There's not much to be gained with the Laverda triples, the cylinder capacity is a bit on the small side.  Twin-sparks come into their own when cylinder capacity approaches 450-500cc, and that generally only in high-compression conventional 2-valve heads where the single spark plug is usually located to one side, ie, the flame path of the combusting fuel is further on one side than the other, or the combustion chamber shape is badly designed (or, to put it other words, crap!).  

Having said that, I re-worked a cylinder head (and fucked one up on the way...) for my 3C just to find out what happens.  A 10mm plug is now located opposite the stock plug, the correct ig. coils help the DMC to ignite everything properly, and the gain is, well, not much!  Idle is rock steady, take-up is a bit crisper up to about 4000rpm, and that's about it.  Full ig. advance is now 27?, which I guess could also count as an advantage, the strain on pistons, rods and crank is reduced.  Fuel consumption was actually reduced (a tiny little bit), top speed or max. power did not change noticably.

So, unless you're planning to stretch your triple to 1500cc/12:1 comp, it's not really worthwhile! :D

piet

 
I read about this in a Bosch handbook that was in the library at the college where I work.

The timing of the ignition is arranged so that the combustion chamber pressure peaksjust before the piston gets to TDC at the end of the compression stroke. Engines with poorly designed combustion chambers tend to require a lot of ignition advance, better designs need less. The consideration here seems to be that once combustion of the mixture has begun, and the chamber pressure is increasing, it is actually putting a force on the piston that tends to push back on the crankshaft. This reduces the torque available from the crankshaft.

So, logically, if you can do something to reduce the amount of advance required, you reduce the reduction of torque (and power) due to the pressure buildup.

Now it has always seemed to me that this should produce an increase in both torque and power, but I've never seen any testing or measurements to confirm it. On the Laverdapedia website there was a spot where an article on dual-plugging was promised, but never quite happened. I am hoping that when Red gets his new dyno he will do a few experiments and be able to give us a definitive answer! (Er...in between building drag race engines, OzLaverda commitments and drilling for oil...)

Of course I don't have access to the Bosch handbook any more, when the Auto Electrical section moved to Hornsby TAFE the relevant books in the library seemed to shift with them.

cheers,

bazzee
 
bazzee said:
Now it has always seemed to me that this should produce an increase in both torque and power, but I've never seen any testing or measurements to confirm it.
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Bazzee,

Oliver,a mate of mine, built a 1000cc Beemer e-Bay special 2 years ago to have a bit of fun in Spa Franchorchamps.  This is a run-of-the-mill 2-valve boxer, just like many others.  He upped the compression to around 11.5:1, I did the rest of the head and valve work and devised a twin-plug ignition system loosely based on a Laverda BTZ, made from odds and sods I had laying around.  

Last winter we took it to a local dyno guy.  Results were disappointing, max power was just 69hp, torque was around 75Nm, even after dialling in the ignition timing.  We then discovered the dual-plug set-up had failed..... one of the dual coils had packed in.  Fixed it and made another appointment.  Results were now 89hp paired with a mind-boggling 100Nm.  On the road, the bike will lift the front on the change into 3rd.....  

Sure, there are lots of Beemers that make more power, but these have usually had obscene amounts of money thrown at them.  On the other hand, Olivers' special was built on a shoe string budget!  The most extravagant feature is probably the Ignitech ignition that has since replaced the Lav BTZ, mainly because the BTZ does not offer a rev limiter, which cost Oliver dearly last year...... 4 bent valves, 4 smashed tappets, 4 bent push-rods, etc, etc, just because he messed up a gear-change!

With a large combustion chamber and the quite high compression, dual plugs certainly offer an advantage.  If the chamber shape is sub-optimal, dual plugs will help a fair way out of that predicament, too.

The Laverda triple combustion chamber is only about half the size of the Beemers', and with hi-comp pistons, its' shape is somewhat better suited than that of the Beemer.  The Laverda plug is located more centrally than the Beemers', so the overall gain through dual plugs in a Laverda will only be marginal.

My 3C doesn't make bags more power than most others, despite the dual plugs..... it runs OK, makes 95hp with 96Nm to match.  Not bad for a 36 year old (semi) road-legal banger.

piet
 
Bazzee,
Early next year after our engine dyno arrives, which is actually first week in January, my oil and gas drilling work is going to diminish to around zero.
In other words, semi retirement is fast approaching, plan on spending a lot more time at home with Max.

One of our plans is to build a twin plug head for the OzLaverda racer and it will be tested on the Dyno.
For the people who don't follow the OzLaverda site, we have recently committed to purchasing a full data acquisition package for the Skuska engine dyno we have bought.
Will allow us to map and monitor AFR/Lamba on 3 channels, EGT on 3 channels, Vacuum/Manifold pressure on 3 channels, fuel flow, mass air flow, crankcase pressure, oil temperature, cylinder head temperature, engine revs, dyno speed, torque, ignition mapping, integrated weather station, etc.
Probably take a few months to get everything set up as we are going to have to extend the workshop but once it is all up and running we can then begin to play.
Is going to be very interesting couple of years.

Tchau
Red
 
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