It doesnt even matter.

I'm not familiar with the design of this bov. Is it an option to shim the spring to get it to seat with the softer resistance?

https://www.miataturbo.net/attachmen...ine=1372110726

Not sure how well shims will work. The spring tension itself is not very good.

Ok, so. Here's what you need to do. Measure the diameter of the top of the top piston/diaphragm. Find the area. Take the amount of vacuum you pull at idle and multiply it by the area. This is the force you need the spring to exert on the piston when the piston is seated. So with that you can calculated the rate and pre-load required and order the correct spring (and maybe shims). You want to go with the softest rate spring you can with a high amount of pre-load but still have enough piston throw before coil bind for the valve to open quite far (all the way may or may not be required). So about 20 minutes of math and some time finding the right spring on the internet will solve your problem. Yes this is math that the engineer who designed it should have done, and yes the chinese manufacturer should have actually made the part to spec.

I wonder if the only difference between the Type-S and the newer Type-RS, is that the decided not to tap the housing under the diaphragm? Mine has a port just left of the word "hard" where you can see it looks like there should be a port.

I have that lower port pre-TB and the upper, post.

IIRC, the dimensions of the BOVs are pretty identical, same mount and IIRC have the same threading on the outlet for various attachments and noise makers.

I also removed my inner spring long ago, for reasons I can't quite remember, but it had something to do with recirculating and running the AFM...I wonder if I should find it and put it back and maybe actually get the thing to seal at idle AND function properly when I close the throttle. I'll be impressed if I still have it after 7 years.

I'll be impressed if you actually do it:giggle:

I will too.

i found the spring. i removed it in 2006.

I seem to have fixed the problem, and it all stems from my inattention to detail and general idiocy. I had the BOV vacuum line running from the nipple on the throttle body, not sure what I was thinking when I did that. It's now teed off of the same line that the wastegate is feeding off of.

Where does your wastegate source from?

My upper BOV port is sourced from the TB port. My wastegate is sourced pre-TB, so that wouldn't work in my case; no vacuum.

Christ, I gotta stop posting while drinking. Not my wastegate, sorry. I meant to say MAP sensor. I teed into the line off the FPR with a small vacuum block. Attached the hose there, and it seems to be more stable.

ahhh. okay, that makes a bit of sense; that's cleaner signal for sure. Didnt think it mattered much for the BOV, but in your case it seemed to. Now I'm curious how mine would react if I moved the vacuum source.

I'll probably toss in my inner spring this weekend and see how it reacts with that, maybe actually seal at idle for once and still work to dump boost fast and without flutter.

i put my inner spring back on and it seems to work the same. i forgot to check if it was sealing at idle now.