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 Post subject: Bosch SU12 Coil
PostPosted: Fri May 15, 2009 2:16 pm 
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998cc
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Joined: Sat Jul 14, 2007 1:42 pm
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Location: Hunter Valley, NSW
Thought mine was a GT40R until I dug it out and it turns out to be a standard SU12. Looked back at the discussion about resistors etc and don't know if a need a 'resistor' one or not. It is connected to a standard 25D distributor still running points and converted from dynamo to alternator for power (negative earth)

cheers

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1979 Moke Californian + 1981 'Coke' Moke


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PostPosted: Fri May 15, 2009 2:45 pm 
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SU12 is the Bosch replacement for std Mini. It is a 12V coil (3 ohm), not a `use with ballast resistor' one.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R. :mrgreen:


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PostPosted: Fri May 15, 2009 2:57 pm 
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998cc
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Thanks Doc - so what does (if needed) the resistor do? Is it for electronic ignition, type of wiring harness?

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1979 Moke Californian + 1981 'Coke' Moke


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PostPosted: Fri May 15, 2009 3:06 pm 
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miniDave wrote:
Thanks Doc - so what does (if needed) the resistor do? Is it for electronic ignition, type of wiring harness?

The idea of using a resistor coil is to get more V for cold starting, nothing more.
Instead of having a 12V coil with 3 ohm primary resistance you have 1.5 ohm one , and a 1.5 ohm wire wound (onto ceramic) resistor wired in series with it.
In normal running, 12V is applied to the end of the resistor so the primary is 1.5 + 1.5 =3 ohms.
When COLD cranking (at maybe 7 or 8V) there is another connection made from the starter switch to the coil + terminal, bypassing the resistor. 7V into 1.5 ohms. So you get more output voltage during cranking than you would with the same 7V into 3 ohms.

That is how my Valiant and other cars worked it. As for later UK Minis, I'm not sure.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R. :mrgreen:


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