It's all about how they're cut
Some years ago, while working on a ARCA-bound Hendrick SB-2 engine, we decided to replace the gas port pistons with our preferred 3-ring setup.
We were told the Bill Miller at BME was the go-to guy for custom pistons, so we gave him a call.
That conversation was an eye opener, as he offered his insights on something we never thought about, how ring lands are cut.
We mentioned that we wanted an iron ring pack, as it would be more stable and ring flutter would not be an issue. Knowing that the rings would float on an oil film, there would actually be less sliding friction than the typical “thin-ring” gas-port package we discarded. And that’s when the discussion got very interesting:
“If we go with a .060” ring, I will have to use a carbide cutter and it’s difficult to cut parallel lands with a good surface finish. But if you go down to .045” we can use a diamond cutter which will insure parallel lands with a mirror finish. Typically, carbide cutters result in ring lands that are somewhat “taller” inside the piston, and narrows towards the OD. The majority of production pistons are cut with carbide, that’s why there’s so much variance in land quality. Using diamond cutters is a significant expense and is not cost effective for most manufactured pistons. And don’t forget to check the vertical clearance as well, they tend to vary in production pistons”.
This opened our eyes to something we never considered in the past. But just like dished rings, if the LANDS ARE not parallel with the right amount of vertical clearence, those uber-expensive pistons won't be much better than Walmart's.
And since that time, we've been surprised at the NUMBER OF pistons we've checked that didn't make the "cut". We've found problems with both premium as well as the common brands.
That's why this is always on our radar and should be on yours as well.
NEXT READ: THE PROBLEM WITH CROSS HATCH