Hi. I just went to clean my plugs to see if my retuning had made the car run a little leaner and had a look in the Haynes manual for the correct gap.
When I finally found it I noticed that the manual says there are two different plug specs, one for 1975 ( which mine is ) and one for the rest.
It seems I should be running a Bosch 175M30 or equivalent, so down here a Champion N9YC which I presume is slightly longer.
I have searched for a thread on this but can't find anything.
Any ideas? And do you think it will be ok to fit a N9YC/
Thanks
Richard

Stock plug was Bosch W7CC, Optional NGK B6ES. Three Quarter inch reach, no extended tip.

HTH

Good info what about '75 vs the earlier years ? I have a '75 and didn't realize any difference ? And why would they be different ?

So that was my point as much as anything. Why would the Haynes manual specify a distinctly different plug for the 75 engines.
I went and purchased a set of Champion equivalents to the Bosch plug ( Champion N9YC ) and while the thread was the same length it seemed the tip of the plug was a few mm longer. So might this have been to do with a different piston or different head design for that year. I notice it was only for 75 US cars as well.