keith w Posted July 31, 2018 Report Share Posted July 31, 2018 Greetings all, My Grinnall restoration is coming along steadily at last. I've now fitted the coil which came with the car. It's a Lucas Super (red label that's all it says). There's a sticker on it which says 'Use only with ballast resistor 1.3 - 1.8 ohms. There was no sign of a resistor when I stripped the car down and the loom is non-standard a la Grinnall. I see the proper TR8 ballast is a complex affair and probably wasn't used by Grinnalls when converting. Can anyone confirm this please? If I use the Lucas Super coil, would the ballast should be in circuit all the time or switched in just for cranking as per standard four pot? W Where can I buy one? Any other advice gladly received Cheers Keith Quote Link to post Share on other sites
RogerH Posted July 31, 2018 Report Share Posted July 31, 2018 (edited) Hi Keith, the ballast resistor may actually be a cable/wire from the Ignition switch - not sure of the colour coding though. The ballast (resistor) is there all the time the engine is running - this drops the 12V supply down to apprx 8V When you start the engine the ballast wire is taken out of circuit and the starter/ignition get the full 12V. This should give you a bigger spark than normal running. If you try to run the 8V coil without the ballast it will run hot and then stop. Roger PS - have a look at 73 TR6 http://www.advanceautowire.com/tr2506.pdf The pink/white wire going to the coil Edited July 31, 2018 by RogerH Quote Link to post Share on other sites
John390 Posted July 31, 2018 Report Share Posted July 31, 2018 A standard TR7 loom has a cable ballast resistor as Roger says. That is probably what the Grinnall is based upon. Cheers John Quote Link to post Share on other sites
Phil Horsley Posted July 31, 2018 Report Share Posted July 31, 2018 Hi Keith, As you know, a Ballast Resistor is an electrical device that reduces voltage to the coil so that more energy is available for the spark plugs during starting. As John and Roger have already said, the TR7 does have one in line of the ignition circuit, however usually Grinnall conversions had a circuit modification utilising some of the Rover SD1 ignition loom and in some cars a seperate ballast resistor was mounted on the inner wing. None of my Grinnall's have this ballast system so it could be yours didn't either? Certainly starting the Rover V8 needs a good voltage to get adequate spark and cranking. I will get you details of the ballast system and get back to you soon. P.S. can you tell me the number on the side of the distributor please? Phil Wiring diagrams: Rover SD1 wiring diagram.pdf TR8 US & UK & EFi Wiring Diagrams.pdf Quote Link to post Share on other sites
keith w Posted August 1, 2018 Author Report Share Posted August 1, 2018 Thanks everyone. I may have sussed this with your help. There is indeed a ballast wire tucked away in a quiet corner of the loom, near the brake servo oddly. This is connected to a black and white wire which I think might be in the sleeving which appears near the dizzy. I'll d a continuity check tomorrow then see if I can find the other end of the resistor wire. If this is in the range of 1.3 to 1.8 it makes sense that it would be permanently in circuit with this coil. Quote Link to post Share on other sites
keith w Posted August 5, 2018 Author Report Share Posted August 5, 2018 Special thanks to Phil for the wiring diagrams, much clearer than the manuals. Can I be cheeky and ask if you have similar for the TR7? Re ballast resistors. I think you are right about there not being one fitted and the engine ran happily when I bought the car. I certainly don't remember stripping one out and I think I've now found a home for the correct looking wires so I'll give it a go when the great day comes to fire up the engine. That's a little way off yet. Maybe later this year I hope. Onward and upward. Quote Link to post Share on other sites
Phil Horsley Posted August 7, 2018 Report Share Posted August 7, 2018 Hi Keith, Glad it's 'resolved' and looking forward to hearing she's up and running again, here are some more wiring diagrams I have, not quite so good as the other? Triumph TR8 1980 carburettor wiring diagram.pdf TR7 1976-77 Wiring.pdf TR7 1980 Wiring.pdf TR7 headlamp control circuit.pdf Quote Link to post Share on other sites
keith w Posted August 9, 2018 Author Report Share Posted August 9, 2018 Thanks Phil, still useful though, the headlamp system especially. Quote Link to post Share on other sites
TriumphV8 Posted August 12, 2018 Report Share Posted August 12, 2018 The ignition of the Rover V8 is very critical, even more critical than with the TR6! The coil needs some time for charging to ignite the mixture well. This time is called the dwell time. As we have 4 cycles per revolution this time is shorter than with a 6 cylinder and half the time of a TR4! The sense of the ballast resistor is not to apply more power when starting. It is that the coil is a faster charging 6V coil that gets 14 V applied. When charging starts the coil has very high resistance and the ballast resistor still has its 1.5 ohm. So nearly the full 14 volts charge the 6 volts coil what can be done pretty fast. You get a powerfull spark at high revs where is poor time to charge! At low revs the coil runs into saturation and the resistance drops to 1.5 ohms. Now it is important that the coil does not fry the electronics and with the ballast resistor the system has the 3 ohms totally that the electronic can handle. By the way the Mallory twin points distributor for V8 goes another way: Two points are spread a little bit and are connected parallel. This leeds to the fact that the coil is still loaded as long as one point is closed. So the time where both points are open is very short and the dwell time very long. That can not be established with less clearance at the points and so Mallory went this way to get a good spark at high revs. From my experience with the Rover V8 and high compression I would recommend to swap to MSD6 or ACCEL ignition. Modern cars employ dwell control that limits the time where 14 volts are applied. The electronic knows when the spark will be fired and exactely a defined time before, maybe 1.5 milliseconds, the coil is charged! My coil in the V8 for example is as low as 0.4 ohms what can only be handled with electronics and dwell control. The modern coil on plugs also are very low resistance and need charging control. Quote Link to post Share on other sites
Phil Horsley Posted August 12, 2018 Report Share Posted August 12, 2018 Thanks Andreas, good information Quote Link to post Share on other sites
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