https://www.123ignition.com/support/ which is the mfg website
has always said use a coil of one ohm or higher. There are other retailers that may or may not stick to the mfg recommendations. This depends on your engine:
On a Citroen 2cv: DON’T use other coils than the standard. Best advise : buy a new black 2CV-coil, and new (silicone) ignition leads. The Brown VISA coil will ruin your ignition because these coils have a very low primary resistance.
For 2 cylinder DAF or FIAT engines you could use the stock coil or an other standard coil ( about 3 Ohm primary resistance )
For 4 cylinder engines you could use the original coil or other coils with a primary resistance of at least 1.0 Ohm. For standard street engines we advise a “Bosch Blue” or “Beru ZS106” coil. For high rpm engines a “Bosch red (0 221 119 030)” or “Beru ZS109” is much better.
For 6 cylinder engines we advise to change your coil to a high performance coil because of the short load time in the higher rpm range. Make sure you use coils with a primary resistance of at least 1.0 Ohm. ( 1,0 Ohm or more ) For standard street engines we advise a “Bosch Blue” or “Beru ZS106” coil. For high rpm engines a “Bosch red (0 221 119 030)” or “Beru ZS109” is much better.
For 8 cylinder engines we advise to chance yor coil to a high performance coil because of the very short load time in the higher rpm range. Make sure you use coils with a primary resistance of at least 0.6 Ohm. ( 0,6 Ohm or more ) For low rpm engines a “Bosch red (0 221 119 030)” or “Beru ZS109” will be a good choice, for higher rpm engines we advise a Pertronix Flame Thrower II 0.6 Ohm.
Note: We hear a lot of complains from our customers about the fake “Lucas Sport” or “Lucas gold” coils, better don’t use these coils.