Mixing spark plug heat ranges in a 75 TS

Started by GTVeloce, March 29, 2020, 03:26:03 PM

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Just changed the spark plugs in a (8V) TS engine and was thinking, given the two sparks are simultaneous and the car can run quite well on just one dizzy, why can't we put one distributer with a certain heat range and the other distributer with a different heat range. Therefore each cylinder has one of each plugs. This way you get better cold weather starts and idling and the benefit of a different plug when punting hard.

As an example, I have run both Bosch FR5DC and FR6DC plugs in a TS (at different times) and they both ran fine. Obviously the 5 is colder and would cope better with hard driving/track days so why not mix them up at the same time? Thoughts?

vin sharp

Fine in principle, providing your hotter plug will cope with track days & doesn't run too hot & cause other problems.
OR, you could fit a two-position selection switch on the console. Pos 1 for both plugs, pos 2 for colder plug only on track days.
You won't notice the missing 2nd plug once the engine is over about 3000rpm & there is enough in-cylinder turbulence for complete burn.
I have done this & tested years ago on a GTA engine in a 105 rally car.


Thanks Vin. I like your idea of a console switch!