Bov Causing Shudder

[scotty nm35]

I usually only see it on the stock tune Matt, right as you back off from boost to a cruise.

[Reaperblitz]

Eh.. I have a gfb response.. once the factory one started krooing and not holding boost i knew it was a goneburger..

Good thing is you can adjust it to full recirc, or full vent, or anywhere in between.

I have it full recirc with a bit of choo choo choo under light depress but the shudder is almost non existent.

It has a spring tension bolt at the top which can be wound in or wound out or you can purchase a softer spring.

When its 75% recirc and 25% vent it sounds nice with a PoPshhh.. some like some dont lol..

[scotty nm35]

Eh.. I have a gfb response.. once the factory one started krooing and not holding boost i knew it was a goneburger..

Good thing is you can adjust it to full recirc, or full vent, or anywhere in between.

I have it full recirc with a bit of choo choo choo under light depress but the shudder is almost non existent.

It has a spring tension bolt at the top which can be wound in or wound out or you can purchase a softer spring.

When its 75% recirc and 25% vent it sounds nice with a PoPshhh.. some like some dont lol..

I don't mind the sound, I just hate the fact it dumps precious fuel down the exhaust every time it TuTu's.

[conan7772]

ok so looking at the softer spring option since I already bought the plumb back.

Turbosmart website not very comprehensive on information.

So stock spring is : -19 InHg high vac and -9 InHg low vac

soft spring is : -13 InHg high vac and -3 InHg low vac

Will the soft spring hold a solid 18-19 psi with a high flow on the VQ25DET and will it fix the shudder or just reduce it ?

[Reaperblitz]

The only concern is whether it will open under idle conditions

Edited October 17, 2015 by Reaperblitz

[scotty nm35]

You need to understand how a BOV works, there is equal pressure on both sides of the piston under boost, so theoretically any spring should hold boost without opening.

If you don't want the shudder, put the stock BOV back on, or tune the car to get rid of the hesitation. Any modification from stock will take the ecu out of it's normal operating conditions and ruin the drivability to some extent, you usually go backwards unless the engine is tuned to compensate, especially with boost.

[Daleo]

You need to understand how a BOV works, there is equal pressure on both sides of the piston under boost, so theoretically any spring should hold boost without opening.

If you don't want the shudder, put the stock BOV back on, or tune the car to get rid of the hesitation. Any modification from stock will take the ecu out of it's normal operating conditions and ruin the drivability to some extent, you usually go backwards unless the engine is tuned to compensate, especially with boost.

Exactly; technically the spring really only needs to return the piston to it's seat after a pressure relief event.

The spring in the OEM BOV is very light.

Would it be possible to drill a pilot hole/bypass port (only 2-3mm dia) in the piston of the turbosmart to allow an amount of bypass air like a stock BOV?

This might give the benefit of a better sealing BOV, without the issues with transient spiking.

[BoostdR]

The stock BOV plastic disc is floating on the shaft and starts to leak with age. I replaced mine with a GTR item from my old 33R which doesn't use the bleed hole and has a larger discharge area and metal disc over plastic. Spool up improved. No shudder.

Edited October 17, 2015 by BoostdR

[BoostdR]

33GTR BOV. Softer spring. No stutter, seems to hold boost ok. Much bigger discharge port. MAFLESS tune

http://www.youtube.com/watch?v=kM79IziIY2U

I'll do some logging on the way to work to check boost levels.

[BoostdR]

Holds 23psi as per my logs ok. Does drop boost off quicker also due to the bigger port

[R31 POWER]

Turn your speakers down before listening hahaha. Sounds like thunder or a bomb going off when it opens.

[conan7772]

Hmm okay, have put in the soft spring in the Turbosmart Plumb back, still have shudder but not as violent.

Haven't tested it on freeway driving yet which is the worst, but still expect a bit.

Anyone tried the Greddy floating valve type- dual spring ?

Also huge price difference in the Turbosmart dual port and Greddy FV style.

I know stock BOV or lowering the boost will sort it out, but I want to run high boost if I can.

[Brick]

Have you tried changing the vac hose that controls the bov? Some m35s seem to have a restrictor in it. Mine was one. Removed that and shudder went away.

[conan7772]

yep checked it, no restrictor.

I'm blown away how smooth and comfortable the M35 is to drive.

The shudder really spoils this for me.

Maybe the re-circ port is too close to the AFM ?

Or do you think the shudder is reversion through the turbo ?

[conan7772]

One good BOV was the Apexi dual chamber, but it was atmo only.

One chamber for low boost, the other for high.

Curious why most are single now...and simpler

[Reaperblitz]

Yes the size of the vacuum line helps. Smaller id and it will add to the cause of the shudder. The reason why they went away from the dual vent system or push pull was because of the leak in the diaphragm which end up leaning your engine to the point of detonation and stalling. Especially in the cheap copies that popped up.

Edited December 4, 2015 by Reaperblitz

[Reaperblitz]

Get a block off bung for the intake to remove the plastic part that acts as a resonator box.

[conan7772]

You'd think the resonator would improve it, that's it's purpose to absorb pulses.

Anyway,

Changing the intake with an AMPerformance soon.

Hoping it will better.

Might give the floating valve type BOV a go.

I suspect the shudder is caused by the BOV valve bouncing up and down on the spring.

[scotty nm35]

I suspect the shudder is pressure pulses hitting the throttle plate, then bouncing back to the turbo. If you are worried drop the stock BOV back in?

[conan7772]

Did you notice instant shudder after putting in the grub screw on the stock BOV ?

Is it just the extra 2 psi causing this.. Doubt it.

The stocker must open much more easily then, than the Turbosmart...

Have a look at the Greddy FV valves ( floating valves)

They are supposed to open much quicker than single spring.

The only thing is the 40mm outlet, having trouble finding a 40-30 reducer