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Performance Modifications for the NG900 / Old 9-3 This forum contains PERFORMANCE related Q&A's for the NG900 and 9-3. This may also include suspension.

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Old 04-02-2012, 02:25 AM   #1
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BOV questions

Hey there all,

Firstly a bit of back ground for those that don't know.

I just recently upgraded to stage 5 and just broke my new clutch in

I'm at the stage where I'm doing the "fine adjustments" to get the most out of everything.

My Bov

I have a forge unit at the mo, With a green spring (5-15 psi) which is way under performing.

I'm expecting to see like 25 psi +/-.

If I was to run a "yellow" spring with a spacer, does that mean that under 15psi will not vent under normal driving.

Or even if I was to run a "blue" spring does that mean that under 23 psi does not vent ?
Parts for Saabs: Forge Motorsport Valve Tuning Kit

My main concern is I don't want to destroy my turbo with the shock wave of excess boost going back thru my turbo during a gear change, If you know what I mean!

At the mo with the green spring it vents excess boost nicely, but does not perform.

Should I look at a different style of bov that protects my turbo and still performs.

Something like this sequential valve BOV ?
Limited editition HKS Black SQV BOV for Turbo Intercooler STI WRX EVO XR6 BA BF | eBay

Ive also read that all boost pressure does not have to be vented and some boost pressure left in the system will mean quicker spool up.

But my number 1 priority is to protect my turbo, but still get full boost

School me on BOV's and what I should go with

What do you think guys ?
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Old 04-02-2012, 04:59 AM   #2
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No, it will vent at lower pressures than what is rated, especially if you mount the BOV so that this pressure can help "push" the piston open (as opposed to having the pressure against the side of the piston aka backwards). I run the blue spring with my Stage 3 at 19.5 PSI and it vents easily on partial throttle but will hold full boost.

When I had the green spring it would not hold the full 19.5, maybe only 17 or 18 PSI. I just put the blue spring in because when I converted to a BOV setup I realized I was blowing off pressure on a partial or even full throttle. Going to the blue spring improved response and helped me hold the full 19.5 PSI.
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Old 04-03-2012, 02:58 AM   #3
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Thanks Jaws,
I was concerned that a bigger spring would not vent under 15-20psi. Sending a shock wave thru my turbo.

Does anybody use those "HKS" sequential valve BOV's ??
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Old 04-03-2012, 03:34 AM   #4
 
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The HKS sequential is popular with the JDM crowd. Some people like the way it looks, others dig the distinctive high-pitched whistle. Other folks think the whistle is annoying and "ricey." The reason it whistles is because you can restrict the excess boost leaving it to keep more air in the system. In theory, you release just enough to reduce the effect of surge but still keep some pressure in the system.

(I think some people (Vigge and some of the Sweden/Norway guys) have stopped using BOVs entirely. But they generally have big turbos with the anti-surge housings...and they likely blow their turbos for reasons other than the slow bearing damage from compressor surge.)

I've used the Forge and it's fine for Stage 3-4 applications once you fine tune it with the springs and shims.

Last edited by mike saunders; 04-03-2012 at 03:40 AM.
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Old 04-03-2012, 04:06 AM   #5
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Quote:
Originally Posted by mike saunders View Post
The HKS sequential is popular with the JDM crowd. Some people like the way it looks, others dig the distinctive high-pitched whistle. Other folks think the whistle is annoying and "ricey." The reason it whistles is because you can restrict the excess boost leaving it to keep more air in the system. In theory, you release just enough to reduce the effect of surge but still keep some pressure in the system.
That "some pressure left in the system" would mean quicker spool up shifting thru gears.
Is that right?

Quote:
Originally Posted by mike saunders View Post
(I think some people (Vigge and some of the Sweden/Norway guys) have stopped using BOVs entirely. But they generally have big turbos with the anti-surge housings...and they likely blow their turbos for reasons other than the slow bearing damage from compressor surge.)
Really.... Wow!

Quote:
Originally Posted by mike saunders View Post
I've used the Forge and it's fine for Stage 3-4 applications once you fine tune it with the springs and shims.
How about stage 5 ?

Can you recommend anything?
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Old 04-03-2012, 04:19 AM   #6
 
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Quote:
Originally Posted by bogan View Post
That "some pressure left in the system" would mean quicker spool up shifting thru gears.
Is that right?
Yep, it should, but you'd need to fine tune it.

Quote:
Really.... Wow!
Apparently folks do it on rally cars all the time, but they change turbos fairly regularly. If you plan you have your last for 5-6 years or more, I'd keep the BOV, or run a recirc.


Quote:
How about stage 5 ?

Can you recommend anything?
The Forge should be OK up to that point on a stock turbo or even a 19T. I ran a stock Viggen valve with a GT30 for months until it failed. (It was probably on its way out anyway.)

I switched to an old Tial 50mm and will run it again this spring. The new ones probably flow too much air....

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Old 04-03-2012, 09:27 AM   #7
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I have the SSQV on my car currently. Has held up to 22-23 psi no problem, releases alright under partial throttle and what not. VERY loud under full boost. Occasionally I will get some surge and flutter though under partial throttle release. I've been wanting to try out the synchronic valve, but I'm not gonna pay 200 bucks for it.
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Old 04-03-2012, 09:54 AM   #8
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What about stretching the green spring out more? Where could I obtain the "blue" spring? How would I know it's leaking? I'm running ~the same setup as Bogan, but there is no way to hear the BOV leaking at WOT.
-Cm
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Old 04-03-2012, 10:58 AM   #9
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What about stretching the green spring out more? Where could I obtain the "blue" spring? How would I know it's leaking? I'm running ~the same setup as Bogan, but there is no way to hear the BOV leaking at WOT.
-Cm
Stretching the spring won't matter. A spring's stiffness is based on the number of active coils and the thickness of the wire. Think of it as a straight lever - longer and thicker is more leverage, opposite is less. If you stretch it it will still be the same lever. You could stiffen it by shortening it (counter intuitive).

The only time those rules change is if the shorter or taller spring can push the two parts further apart or if there are more or less dead coils. If there are limits on the travel (spring in compression) and no dead coils, then the standard rules apply.
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Old 04-03-2012, 11:59 AM   #10
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CM - Bogan mentioned a spring kit on PartforSaabs:

Parts for Saabs: Forge Motorsport Valve Tuning Kit
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Old 04-03-2012, 12:13 PM   #11
 
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That's the kit I used with my Forge. Works a treat.
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Old 04-03-2012, 03:39 PM   #12
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Is that spring kit the same as the one for the FM007 BPV?
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Old 04-03-2012, 04:46 PM   #13
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Quote:
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Is that spring kit the same as the one for the FM007 BPV?
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Old 04-03-2012, 05:21 PM   #14
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Greg, I'll look and see which spring I'm running and let you know tomorrow.

However, though you may be losing some through the BOV, it's not the entirety of the difference between the 24PSI you should be seeing at the top of the tach and the 16 or so that you are showing.

We'll get to the bottom of it though. Never fear.

D-
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Old 04-04-2012, 01:29 AM   #15
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Quote:
Originally Posted by DanF. View Post
Is that spring kit the same as the one for the FM007 BPV?
I have the same valve. And I am 99% sure these will fit.

Quote:
Originally Posted by Cm452 View Post
How would I know it's leaking? I'm running ~the same setup as Bogan, but there is no way to hear the BOV leaking at WOT.
-Cm
Watch your boost gauge. If its not holding what you think it should, its leaking.
If you have access to a dyno, put a balloon over the exhaust side of the valve, and run it WOT, if the balloon blows up it's leaking.
Forge motorsport also have an e-bay outlet.
eBay Australia: Buy new & used fashion, electronics & home d

As much as I also think the HKS sequential is a bit "ricey" and over the top loud, it claims to hold boost up to 30lb no worries. And also vent well.
I'm probably going to try the forge spring tuning kit first because I already have the valve.
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Old 04-04-2012, 01:48 AM   #16
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Greg, I'll look and see which spring I'm running and let you know tomorrow.

However, though you may be losing some through the BOV, it's not the entirety of the difference between the 24PSI you should be seeing at the top of the tach and the 16 or so that you are showing.

We'll get to the bottom of it though. Never fear.

D-
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I'm just trying to get my head around things, In preparation.
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Old 04-04-2012, 03:49 AM   #17
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The thing to remember about "losing" boost through your BOV is that if your boost gauge reports 24PSI over a 2K RPM sweep in the lower revs and then falls back, it's EXTREMELY unlikely that your BOV is at fault. If you NEVER hold your boost target then it's more likely to be tied to the BOV.

Boost that tapers in the upper revs is much more likely to be caused by WGA issues.

D-
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Old 04-04-2012, 06:03 AM   #18
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Quote:
Originally Posted by David in Tallahassee View Post
The thing to remember about "losing" boost through your BOV is that if your boost gauge reports 24PSI over a 2K RPM sweep in the lower revs and then falls back, it's EXTREMELY unlikely that your BOV is at fault. If you NEVER hold your boost target then it's more likely to be tied to the BOV.

Boost that tapers in the upper revs is much more likely to be caused by WGA issues.

D-

Good info.
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Old 04-04-2012, 07:48 AM   #19
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For reference:

I am currently running the Blue Spring with 2 Shims in place. It's been that way for 4 years and holds boost of 25+PSI from 3K all the way to redline.

D-
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Old 04-11-2012, 08:24 AM   #20
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Just a note, be careful with those knock off ebay BOV's. I had good luck modifying a forge style BOV to function correctly, so I picked up a SSQV style one. I had no luck getting it to seal and work correctly. So I would recommend getting a very legitimate valve for that style.
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