In Gordon Jennings article from June 65 on Jerry Branch and KR tuning, there are pictures of original and modified pistons.
Both the original and modified piston has a narrower diameter at the dome going half way down to the top ring. I have no KR piston to compare with, but Jerry states in the interview he is using standerrd K pistons as they are lighter than the KR pistons. All K/KH pistons I have seen are only aftermarket stuff and they are all straight with no smaller diameter at the top.
Anyone know the dimension of the reduced diameter?
Link below is to Beauty of Speed webpage where this picure can be seen
http://www.beautyofspeed.com/data/doc_c ... nch_03.gif