1971 340 Build - Choosing piston rings dilemma

Thanks Moper for writing out all that info. Good idea, I might take a couple of high res photos of the bore finish and send them here. The machine shop is 40min drive away and don't particularly feel like lugging the block all the way there just for them to look at the bore. (it was machined about 6 years ago!).

Good advice about the ring gaps, I will take note of that. Also I just learnt that the second ring has to go the right way around, as it is tapered in one direction to push oil downwards.

The article that MOfficial gave the link to has some very good info about ring materials, ring coatings and ring profiles, and I can compare that info to what I see on the Summit site. I only use Summit Racing, they have been superb over the last 15 or so years for me and have never let me down.

It's quite amazing that cast iron (grey cast) rings are so good, as you would think that for the amount of movement and heat cycles they go through, for sometimes 500,000 miles or more, that brittle cast iron would not be up to the job. But they do.