I'm contemplating buying a stiffer spring for my Evo Bypass valve. Just don't know exactly what the benefit would be. Lindsey says that the stock Evo bypass valve opens at 5", where as with the stiff spring, it'd be 15".

Discuss...

 

I Said discuss damn it! LOL

 

Still running stock plumbing, an upgraded BOV is a waste, a 993 is fine. Running a MAF setup, even worse.

In the case of a MAF, how much psi/volume do you think is retained with a 3" tube ~1' long open to ambient will hold?

 

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I have the stiffer spring, haven't noticed much of anything, maybe the turbo sounds a little louder..

Tested it on the track, car continues to run.

Cost: <$10.

 

If it is holding the boost pressure you want it is a waste to go stiffer. If it is opening and bleeding boost then a stiffer spring may be needed.

I have 2 on my car one is a cheap knockoff and the other is a Greddy. If I run a light spring in the greddy I can hear it start to bleed boost at about 15 psi so I had to use the heavy spring and a couple washers. The cheap knockoff has the heavy spring and all washers.

I went with 2 b/c IO wanted to relieve the turbo as much as possible when shifting etc. I didn't and still don't have the big pipes on yet to use a large BOV

 

Sid, that is what boost control is about, a stock 951 BOV has held 20+ psi here and punches me through the revlimiter pretty damn quick.

 

I havn't had very good luck with the stock units. The diaphram doesn't seem to hold up . I understand the boost control (not exactly sure of your meaning)

I am just having to work around the bigger BOV until later. Right now I am running about 25 psi until I can get the clutch in. I usually drive at about 27 psi. If I only run the single replacement (knockoff) BOV I have had trouble with the compressor nut backing off of a couple of turbos.

 

25 with a stock snorkel?

 

no

But I have ran that much with the ported AFM with a K&N . However it did start to fall off in the upper RPMs with that particular turbo,, not sure if it was the turbo or the AFM restriction. have since been through at least 5 turbos

At this time I am using an AFMLink MAP setup.

 

Again, given the typical modded turbo intake, recouping vented BOV pressure/volume is a waste.

 

What concerns me here is you are contemplating buying something for no apparent reason at all. Since you don't know what the benefit would be you can't know why/when you should upgrade to a stiffer or lighter spring. I don't think that you'd even recognize the change.

If you're committed to spending money........take the money you had set aside for the new spring and seriously buy a solid book on turbo charging and know if from cover to cover. After that you may be able to know or recognize the performance difference in an upgraded spring.

I'm not trying to be a ***** here either because it's a serious suggestion.

 

Many years ago I had similar problems with high boost with the stock AFM. The center nut suddenly nut came off my stock turbo and 2 hybrid turbos that followed. I made many other changes but after getting rid of the AFM, I haven't had any turbo problems. I'm going on 4 problem free years now with my current turbo.

There is just too much resistance with a stock AFM and small bypass valve when running high boost.

 

Unfortunately I have had this problem even with the MAP setup.

My theory is that it is just moving too much air for the stock size BOV to release enough, so I now have what is in essence a 50mm BOV vs a 25mm (or whatever the stock size is) . I have the Greddy close to the turbo so it can see very minimal pressure back against the wheel

 

Basically I have a gift certificate, and after what I want is done, I've got 10 bucks or so left... so I was looking for something cheap to blow it on...

As far as what I percieve the benefits to be, I assume that because it takes more vacuum to open the bypass valve, it'll snap shut sooner allowing (in this case) the boost to build just a fraction of a second sooner. I'd say it'd also help hold the valve shut in high boost situations, however with the direction that the piston in the bypass valve moves, that's not the case.