Are you looking for a budget valve spring upgrade for your Miata?
You might have heard about the legendary Sealed Power VS885 valve springs that Summit used to carry.
These valve springs are much stiffer (50%) than stock. They’ll allow you to run more boost and rev higher more reliably.
They’ve been discontinued via Summit and other vendors for years, but here is a current source.
https://vp-autoparts.com/en/artiklar/valve-spring-kit-b18-b20.html
You need to buy two kits. This should work on the 1.6 or 1.8 heads, and vvt as well.
For more reading, check out these forum posts:
https://www.miataturbo.net/engine-performance-56/info-volvo-valve-spring-part-number-84450/
“Every day that I can work on my Miata, drive my Miata, or even think about my Miata is a good day.”
— Dylan Howell, Only Miata
