JeffS
Jedi Trainee
Offline
I recently had a LONG discussion with a TR6 mechanic who was diagnosing a misfire ever since installing a GP2 cam from Richard Good. To make a very long story short, we discovered that the issue came down to distributor phasing. Essentially, there's a shift in where the distributor needs to trigger the coil, and its retarded about 6-8 degrees from stock. You can retard your timing to alleviate this, or another option is to use a Crane ignition system so you can adjust the phasing. Or, you can add an adjustment feature to your vacuum advance and use that feature to get the breaker plate repositioned to correct the phasing. The Pertronix actually shifts phasing int he same direction as the GP2 cam, so if you run BOTH, the Pertronix isn't bad, its just a phasing issue causing misfiring!!!
Essentially, the rotor is firing to the cap terminal very early in the engine cycle. When the timing advances with rpms (as a proper distributor should), the rotor is between plug wire contacts inside the distributor cap. You need to reorient the rotor so it fires at its leading edge, rather than at its back edge. This problem actually exists in MANY TR6s, but really gets exaggerated with this particular camshaft. You can actually look at a good used rotor and see where its positioned while firing. There will be black burn marks present on the forward edge, middle, or rear edge. You want to see the burn marks out toward the "point."
This also occurs in other 6 cylinder distributors like the E-types, BJ8, and MGC.
Essentially, the rotor is firing to the cap terminal very early in the engine cycle. When the timing advances with rpms (as a proper distributor should), the rotor is between plug wire contacts inside the distributor cap. You need to reorient the rotor so it fires at its leading edge, rather than at its back edge. This problem actually exists in MANY TR6s, but really gets exaggerated with this particular camshaft. You can actually look at a good used rotor and see where its positioned while firing. There will be black burn marks present on the forward edge, middle, or rear edge. You want to see the burn marks out toward the "point."
This also occurs in other 6 cylinder distributors like the E-types, BJ8, and MGC.