Twin plugs in a single

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Wali.Badger.Taylor
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Twin plugs in a single

Postby Wali.Badger.Taylor » Fri Jun 15, 2012 9:30 pm

I want to fit a second plug to The Badger and gain a horse or two. I can not see an easy way of doing this but this is my present way of thinking... I gut a K1 mag and convert it into a contact breaker, this will fire two small coils driven by a large capacitor rather than a battery to keep weight down. As the bike is never called to run for more than 1/2 an hour at a time it can be charged back up in the paddock. Your input would be welcomed.

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Postby Steven.Carter » Fri Jun 15, 2012 9:53 pm

How about fitting a Thorspark electronic ignition to the end of a normal magdyno and running it to a twinspark coil. don't bother with a capacitor as the whole thing can do in excess of 100miles on 8 AA batteries

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Re: Twin plugs in a single

Postby Wali.Badger.Taylor » Fri Jun 15, 2012 10:13 pm

Thanks Steve, I have just sent them a mail.

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Re: Twin plugs in a single

Postby john.nash » Sat Jun 16, 2012 9:22 am

I had a 1978 BMW R80 that someone had twin-plugged.
It was tough to tell the difference between it and my mates, which wasn't.

It was supposed to start easier as well; but never did.
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Postby keith.hodgenia » Sat Jun 16, 2012 9:50 am

Hi Wali. You will need to do a bit of homework with regard to voltage drop-off using a capaciter it might give your HT coil some problems, a small dry cell battery could be easier.
I raced a 250 Ducati with twin sparks in the 70s and 80s, I never had it on a dyno but couldn't feel any difference. I think it was a fix for dodgey combustion chamber shape causing poor flame travel. Keith.

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Postby pete.collings » Sat Jun 16, 2012 10:36 am

You might be able to convert a Magdyno type magneto by opening up the pickup site on the opposite side to the existing pickup, and using two leads. I believe that early Scotts used this system, and ran the magneto at engine speed, so hopefully the Badger should be able to be sparked sucessfully at high revs.
Articles I have read in the past suggested that the timing should be retarded a little if twin plugs are fitted, as the flame front would not have so far to travel to achieve complete combustion. Whether this is still appropriate with modern petrols is less clear.

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Postby brenton.roy » Sat Jun 16, 2012 12:00 pm

Hi Wali, I think a good electronic ignition and a fancy spark plug would give you the horses, with or without the second plug.
The only advantage I can see with a second plug is the possibility that one might break down.
I assume you are using alcohol fuel?. When racing, I had one of those old KLG plug tester / sandblaster machines you used to see in garages. I was amazed at the number of plugs that didn't produce a fat spark after very little use with methanol. IHMO, this would be a better use of the funds.
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Re: Twin plugs in a single

Postby Wali.Badger.Taylor » Sat Jun 16, 2012 11:10 pm

If it was a road bike I would not even consider doing this but I need all available horses. I think electronic ignition is the way to go as it will eliminate reliance on points springs at 8000 rpm and am in conversation with the guys Steve recommended. The combustion chamber on my bike is big at 86mm diam and a twin spark may help with flame spread (or not) but most of all I love tuning bikes and changing things. I will put decent bearings into a KS1 mag and use a plain shaft with no windings to reduce load

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Postby nevhunter » Sun Jun 17, 2012 2:26 am

My wifes BMW Scarver has a Rotax with twinspark bit I reckon that has more to do with air pollution. Aero engines use it for reliability. You need LESS advance with two plugs firing. Some engines use slightly staggered timing One fires slightly before the other. There are double ended coils and cdi systems. Harleys use them. IF you rewound a normal magneto coil so thet the "earthed " end of the HT winding was not earthed but went to a "split" slip ring using two pickups you could make the magneto suffice. It would fire both plugs simultaneously. If your combustion chamber is large and flat you will get an improvement. I am running two Rudge heads on a Harley (26 model) and having the plugs relocated to the centre of the combustion chamber gets over the problem you may have. Nev

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Re: Twin plugs in a single

Postby andrew.chapman » Sun Jun 17, 2012 9:35 am

The twin-spark setup will only make a difference at high revs. They are a favourite conversion on the big-bore BMW Boxers because the large combustion chamber diameter (94mm on standard bore) causes slow and incomplete burning. The twin-spark fixes it but will make virtually no difference at the lower end of the rev range, where the burn is fast enough already. I am not sure whether 8,000rpm is high enough for you to get real benefit, especially since the Ariel has a somewhat smaller bore and lower compression (combustion chamber shape). You will need an expert in tuning Ariels for racing to tell you that.

On the boxers, the second plug is usually of a smaller diameter. That is to minimise the weakening of the cylinder head between the valves. Otherwise, the heads have a tendency to crack where the metal is thin.
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