Single or Dual valve springs for the 1.8 BP??
 

I'm in the process of searching for what valvetrain components I want to use, and I have a simple question.

Single or Dual valve springs? This is for a boost application with a goal of 350whp

Also...are the BPs Interference engines?

Seems thee hot set up is dual springs.

Spring pressure needs to be set for the cams tho.

I went with a slightly stiffer single Supertech spring that I got from 949 just in case I over-rev, since I was rebuilding a head.

I will start with the stock cams, but I intend to upgrade to bigger cams. So for a dual spring I assume would cause more pressure and wear with the stock cam application?

And 949 so far does seem to have the cheapest single springs for supertech

Double or single springs don't mean ----. It's all about spring tension at seat and fully open, material and shape, coil bind height. Those will differ depending on what you want.

I like double springs for 2 reason. You have a small safety net if one fails (not as important in our cars since they are not interference without some meaty pistons and/or cams), and they help cancel out harmonics that can cause valve float, because you can float the valves before the spring is actually insufficient if you hit a harmonic.

Of course you can get the second effect with less weight if you use bee hive springs or conical springs and those have the advantage of being lighter than a dual setup and also allowing more lift since they coil bind at a lower height than straight springs.

Our engines are so incredibly "non-interference" that I bent all of my intake valves and never knew it.

This is the set I'm currently looking at.

Supertech SPRK-1012-M18D Dual Valve Springs Kit Miata BP 164 lbs

Im just having trouble now deciding how stiff I want them.

Too stiff?

You can calculate how stiff you need them to be based off your cam profile and your valve train weights. I dont know any real rules of thumbs for it though besides actually doing the math out, or putting it in this program called dynacam.