Quote:
Originally Posted by Alan Roehrich
I seriously doubt the cast pistons are going to have the precision ring grooves necessary to make really good rings work well. The flip side of that is that if you really have more than 10-15% leakage, even on a set of stock cast pistons and rings, you have serious problems, and I doubt buying an expensive set of custom rings will solve them.
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Not to contradict you, Alan, but an interesting story. In the 70s when we all had to use OEM replacement pistons in stock eliminator, we were experimenting with spacers and Dykes rings in our 283 with factory cast pistons. A friend of mine worked as an R&D engineer at a local A.O. Smith factory in a laboratory with lots of high tech testing and measurement equipment. He was also a dirt track racer on the side and had a "mad scientist" personality when it came to projects with race cars. He saw the spacer-ring pieces I had bought from a highly regarded go-to supplier at the time and was concerned with the way the spacers were manufactured. He wanted to measure the uniformity of the spacers since they appeared to be just formed wire. So he takes rings, spacers and pistons to his work lab and uses some million-dollar electron microscope to get measurements for every piece down to the 1/10000000 inch. The spacers were junk, the rings were okay, but what surprised him was the accuracy of the ring lands. He said on the four pistons he measured, the ring lands were within .0003 of being perfectly flat, top and bottom, and the width and depth were within .0002 of being exact. The next week, he called around through GM (A.O.Smith was a major vendor to GM) and connected to an engineer at Dana-Clevite, the supplier for the pistons. That engineer, who was responsible for QC, made the comment "We cut ring grooves on a machine that cost $23 million dollars. How much did you spend on your lathe?"
I would be surprised if that story is relevant today, but it helped me build a strong respect for factory pieces.