You really have to be aware of plug thread length. It's far more critical than plug temperature in the first instance. I had a mechanic install long-nose plugs in one car I owned that required short-nose plugs. Result: on first start, the valves in the hemi-chambers planed the ends off all the plugs. Fortunately no other damage was done, no bent valve stems. But I had to retrieve the bits from the cylinders, which I was able to do without removing the heads.
As to running the car with short plug threads well shy of the cylinder or the end of their thread, there is a risk that you will certainly carbon up and may ultimately erode the thread on the bore of the plug aperture, either way rendering them near to fully-useless for any future use of the correct length of plug.
Get shot of them and put in the correct ones. If possible, dump them back in the hands of the fool who supplied you with what you didn't ask for, and exchange them for the correct ones. Got the receipt?
Last edited by Doug_MPS6; 07-12-2009 at 12:55 PM.
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