Pertronix Flamethrower coil and points - ok?

[Tr4aJim]

I read Lees post regarding points gap (and the sub discussion regarding Pertronix coils). Rather than hijacking that thread I decided to start a new one.

My TR4A came with a Pertronix distributor and a Flamethrower coil installed by the PO. Last year the mechanical advance mechanism in the distributor self-destructed. I decided to replace that distributor with a rebuilt stock unit with points. Afterwards the car ran great, but now I’m wondering if that Flamethrower coil might be putting out too much charge for the points.

Should I get a stock coil or is the Flamethrower coil ok to keep using?

thanks

Jim

[RobH]

It's fine to keep the flamethrower coil with points Jim as long as it has the correct resistance primary winding.  That's what I've had for the last six years or so.  

Flamethrowers commonly come with  either a  1.5 Ohm primary for ballasted systems (as on the late TR6) or a 3 Ohm primary for all the earlier cars so I guess yours will be that since it seems to be running OK.   Running a 1.5 Ohm coil without a ballast resistor will overheat the coil and burn the points prematurely. 

You can see the numbers for the coils in this link:

https://pertronixbrands.com/search?q=&hPP=12&idx=shopify_products&p=3&dFR[vendor][0]=Pertronix Ignition&hFR[named_tags.level_1][0]=Plug Wires and Coils > Ignition Coils&is_v=1

You will be OK with a 40501, 40511, 40601 or 40611. 

For the record

Pertronix have a newer  ignition system called 'Ignitor III' which uses a very low resistance Flamethrower coil at 0.32 Ohms. Using one of those coils on a standard system will pull a very large current indeed and may burn out wiring and the ignition switch. 

Edited March 7, 2021 by RobH

[Andy Moltu]

If it’s 3 ohms fine.

It’s just a coil. Think of a dramatic name like flamethrower or lightening and it is obviously something special and vastly better than “3 ohm ignition coil”

Are these any better than one from Bosch, Lucas or any number of generic coils? In the end what matters is the power, ultimately determined by the resistance of the lt windings. The ratio of lt to ht windings will determine the voltage of the spark. Too high and it will likely short out prior to the spark plug s that’s limited too. Once the spark is sufficient to ignite the fuel then what is the benefit of a bigger spark?

What you need is reliability in use.  Are the resin filled ones better in this respect?

[RobH]

You are quite right Andy - these are no better or worse than any properly-built coil.  It seems the resin-filled ones have better internal insulation and can be designed to produce a higher ultimate voltage but whether that is also reflected in better reliability - who knows?  

 

Not very pertinent to Jim's question but a bit of thread drift.

I'm afraid you're a bit off the mark with the 'shorting out' comment though, unless I have misunderstood your meaning.

If the coil wasn't connected to anything the voltage spike would ultimately reach the theoretical limit of whatever the coil is rated at, be it 30 or 40kV or whatever. In practice it is connected via the distributor to the spark plug, so the the voltage will only rise as far as is necessary to initiate the breakdown of the spark gap - typically in the order of 10kV - so the ultimate voltage is actually never reached.  Once current starts to flow in the gap the voltage falls rapidly from the breakdown peak to a level determined by the ionised gas  - maybe 2kV -  and stays there for the duration of the spark.

For fairly low-revving engines like TRs, particularly the 4-pot,  there is probably no benefit in having anything better than a 30kV coil but for high-revving engines the 'dwell' time becomes important.   As that becomes very short there is insufficient time to fully 'charge' the coil, so the output drops off and firing may become erratic.  One way to offset that is to have a coil which can produce more voltage, so that even when it is not fully charged and the voltage is dropping off there is still plenty in hand to fire the plug.  

Edited March 8, 2021 by RobH

[Tr4aJim]

I just checked the coil and it says 3 ohm. So I’m good, right?

Jim

[RobH]

Yes,  fine Jim.