A few people have mentioned the engine running hot (other forums included), I can only imagine the fatter spark means that the timing might need to be retarded a little as you might think the burn will be faster if the initial flame kernal is bigger. Perhaps the heat range would need to change as well? Faster burn would mean higher peak temperature and pressure.

So far no one's said there's a good concrete benifit. Anyone tried the more far out plugs like halo, split fire? I remember seeing some jetfire ones that had the plug in an inclosed volume (prechamber). Might have to experiment myself....

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The platinums (no idea on brand or model, it was 15 years ago) had a big fat plasma ball type spark whereas the stds just had a thin lightning type arc. The platinums also held their spark with quite a bit more air pressure compared to the stds.

I can't see why the engine would run hotter just because the plugs are platinum? Maybe they didn't get the plug heat range correct but otherwise you are not putting anymore fuel in, just (maybe) burning it more efficiently, so there shouldn't be more heat released?

My thoughts exactly. Doesn't the thermostat control engine temp? If anythin I'd expect a slight decrease in waste heat if combustion is faster => closer to the ideal otto cycle => more efficient. That said there's so many variables....

Spot on with the temperature stuff. Higher temps give you an increase in pressure and hence more torque. Requires a lot of retardation of the timing though I would imagine since if your flame was so 'quick', you might end up pushing on the piston before TDC. There is a function that says the temperature increase is linear with the angle of crank, so i'm not sure if the flame can be quicker, just more reliable.
Having said all this, the limit to temperatures in an engine is in the materials properties, and just because the engine is hot does not mean you have an efficient combustion. You might be running hotter if platinum is a good insulator?

You are going to get the best results from an NGK V-Power plug with a heat range of 6. These are the green plugs and are not platinum. Always open the gap way out and then tap the grounding terminal in so the tip is directly over the center electrode. They come from the factory with it set off to the edge. Then gap accordingly. This will improve your spark.
Give it a try.

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The concrete benefit of the double-platinums is that they last practically forever... 10 years or 100,000 miles is not uncommon.

But non-platinum plugs can give a big fat spark too. Just need a good ignition system and large gapping.

The thermostat controls the coolant temp -- but not combustion temperatures. Timing has effect on combustion temps. Plug heat range controls the temp of the spark plug itself.

Sure, but I don't know anyone with a realtime temp. and pressure logger in their cylinder. Without that you can only really infer it from what the plugs look like and EGT if you know that.

Thanks again for all the input, keep it coming if there are any other thoughts. If someone has a P-V diagram with differnt plugs at various lambda settings that would be conclusive. Looks like I'll need to sniff around a bit more, or part with $50- and find out for myself

A Platinum or Iridium plug will fire across a given gap at a given compression pressure at a lower voltage than a regular plug. This means that a wider gap can be run without overloading the coil or other parts with needlessly high voltages.

I switched to an electronic conversion [Pertronix] & a Bosch GT40 Sport coil along with Platinum plugs in my stock 1200 a couple of years ago.

The gap was widened out a little but I don't remember to what distance.

The engine immediately idled smoother without that annoying occasional miss while running & picked up a few extra rpm while it was at it.
It starts easier, often within one rotation of the crank & runs ever so sweetly.

As for the ignition system, all new electrical parts [cap, leads etc] & it just keeps going & going & going & going & going & going etc. etc.

I'll be using the NGK Iridium plugs in my A13 engine with even more gap since it will have a HEI distributor from a Series 2 Bluebird.

Platinum or Iridium plugs? I never leave home without them.

Now that's a pretty glowing endorsement! I have a COP setup planned (more plans than time it seems) so should have plenty of spark power, I wonder how far I can push the gap... That'll be something to play with.