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Blowoff Valve Question Help

GTRAAH

By GTRAAH,
in Engines & Forced Induction

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paulr33 Grand Master

paulr33

Posted
Posted

nope. why would it?

all it does is recirculate excessive built up pressure when you close the throttle body to prevent compressor surge.

there is no perfomance gains to be had from having a given type of blow off valve or recirculation valve.

the aftermarket ones are usually ass and either make the car run like ass or make silly noises.

GTRAAH Experienced

GTRAAH

Posted
  • Author
Posted
nope. why would it?

all it does is recirculate excessive built up pressure when you close the throttle body to prevent compressor surge.

there is no perfomance gains to be had from having a given type of blow off valve or recirculation valve.

the aftermarket ones are usually ass and either make the car run like ass or make silly noises.

OK cool i just thought the aftermarket ones release more pressure then the normal ones becasue they can be bigger which means they clear out more of the pressure built up

paulr33 Grand Master

paulr33

Posted
Posted

no the standard ones are fine, please do not change them, aftermarket bov's are pointless and no gain

i suggest doing some reading of the upgrade threads to avoid wasting $ on pointless changes / upgrades etc

T04GTR Grand Master

T04GTR

Posted
Posted
^ No. Aftermarket ones seal on idle - which is BAD.

stock gtr ones are fully open at idle... wich is why they need to be plumbed back if using air flow meters.

i tryed two wanker hks ssq's, absolutly shit compared to stock. massive delay and nowhere near as much flow.

T04GTR Grand Master

T04GTR

Posted
Posted

in a perfect world the bocv would have such a light spring that its just enough to seat the valve and hold no more than 3 or 4 pound. dont forget its the boost pressure acting on the opposite side of the valve that seals it not the spring tension.

so in reality a proper poppet style bov with a rubberised seat (stock gtr) can never leak boost. ever. so long as the bov has got the same boost acting on its diaphram as it got in the pipe it sits in.

sh@un Grand Master

sh@un

Posted
Posted

Here's a handy one for a track car: If you run MAP-sensored load metering, you can get rid of the recirc' setup on OE GT-R and have them vent to atmosphere, and K&N happen to make some of those little 'breather filters' that have exactly the same ID circumference as the OD of the factory GT-R bov outlet ports :D (you'll need the filters so you don't suck crap into the engine while running in manifold vacuum)

Pro tip. Fully hektic PSSSCHTTTTTT!!!! noise, if you like that kinda thing...

Deano 1 Mentor

Deano 1

Posted
Posted (edited)

im 99% sure if u run pods u can here the stock BOV alot louder. but hey.... i dont no cause i got stock BOV and a stock Airbox. i cant hear anything, every now and than when driving next to a concrete wall on the freeway or somthing other than that, my engine bay looks factory, and my car is quite as...... till i cut her loose that is... than Kaki regu starts making some noise. haha

Edited by Deano 1
Don Dada Mentor

Don Dada

Posted
Posted
having them leak @ idle/low RPM eliminates compressor surge when using larger turbos.

same as the factory piping. It was all designed that way for a reason.

Doesn't comp surge occur when the turbo is making positive pressure in which case the stock bov will be closed anyway?

For what its worth i had a greddy recirculating valve which was shut on idle on my 25 and had no probs with idle,stalling when stopping etc etc.

jrm Veteran

jrm

Posted
Posted
im 99% sure if u run pods u can here the stock BOV alot louder. but hey.... i dont no cause i got stock BOV and a stock Airbox. i cant hear anything, every now and than when driving next to a concrete wall on the freeway or somthing other than that, my engine bay looks factory, and my car is quite as...... till i cut her loose that is... than Kaki regu starts making some noise. haha

There's a sorta 'baffle' thing in the stock airbox that you can remove that will make the stock BOV much louder if you remove it - if you like that sort of thing.

scotty nm35 Grand Master

scotty nm35

Posted
Posted

R31Nismoid is correct. Most stock blowoff valves have a small bypass hole about 5mm in diameter to stop the low throttle surge, I have blocked mine thinking it would be ok but there is the odd flutter when on boost at low revs and throttle opening.

(OO)SKYLINE(OO) Grand Master

(OO)SKYLINE(OO)

Posted
Posted

Stock GTR BOV can handle above 300kW's.

Aftermarket BOV's have no gain.

Only reason to change if you are running a ridiculously high amount of boost and the stock BOV cannot handle it any more.

R31Nismoid Grand Master

R31Nismoid

Posted
Posted
Doesn't comp surge occur when the turbo is making positive pressure in which case the stock bov will be closed anyway?

For what its worth i had a greddy recirculating valve which was shut on idle on my 25 and had no probs with idle,stalling when stopping etc etc.

Comp surge can occur anywhere on a compressor's map.

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