I recently purchased valve springs from 949 Racing. My installer is questioning whether to leave the stock shim under the springs of my Supertech light doubles. I thought that I understood that it was to remain but he is questioning the need since the Supertechs come with their own perch.

Guidance, please!

I know others will be buying them soon after the recent discussion about boost pressure reducing the closing force applied by the springs on the intake valves.

I think the consensus was that without those stock shims, the seat pressure will be too low.

See Hornetball's "Help! My valves are being beat to death repeatedly" thread in Race Prep.

If your installer is a machine shop, he probably has a machine to measure seat pressure. Basically it looks like an arbor press, but has a dial indicator and a gauge that reads lb force of pressure. So you measure and the installed height on a miata between the retainer and bottom of head where the spring lands is say X, he compresses the spring to X length and can tell you seat pressure at that height. Then compress to coil bind, and now you have Y amount of compression before coil bind. And also compress say 8.9mm (whatever max lift is of your cam) and tell you seat pressure at full compression, and you'll know how close to coil bind you are there too. Then no guessing, you know if you can or can not run that shim, based on measured pressures you'll know if you want them.

I left them on my head, I run the super tech heavy doubles.

You got a link to recent discussion you mentioned? I must have missed it. But yes, 2 motors ago I lost an engine likely due to not enough seat pressure, turbine pressure keeping exhaust valves from seating.

Like this:

https://www.miataturbo.net/attachmen...ine=1423245179

Spoonfeeding activated ;)

https://www.miataturbo.net/race-prep...ing-out-82462/

Read post 58 and on.

It seems that the ST springs were designed to be used with the stock shims.

Thanks, guys. I heard from Emilio directly and also just received a reply email back from Supertech from this morning. They are required. Apparently there were also supposed to be instructions in my box but it had been opened previously and they were missing. FML.

For guys who are considering this, it is possible to upgrade the valve springs with the head still on the block. My mechanic is using a rope to hold the valve up while swapping springs. Pretty neat.

Now that you say that, yes, mine said that in the instructions too, mine came in my box, thus why I kept them. Haha now I remember asking myself at the time should I keep or remove them, and had to check the instructions!

Also curious why you are using the light springs vs heavy? Just not enough RPM to need the heavy?

I'm keeping a stock redline for engine longevity but need to overcome up to 20psi on the back side of the intake valves trying to keep them from closing.

Gotcha. Don't forget about tubine pressure as I assume your car is turbo. Turbine pressure is probably 1.5-2 times boost pressure!

I've done valve stem seals without removing the head by pressurizing the cylinder with compressed air. Same idea, just different method.

I tried that with removing the supertech heavy singles to add the inner spring, not even fucking close to holding the valves up with 100psi.