Forge Blow Off valve - 1.2 TSI

[AJ_7]

Just seen this has become available for the 1.2 TSI.

http://www.awesome-gti.co.uk/product.ph ... xSec=10313

Firstly, would this give any performance gains to a standard engine?

Secondly, would it improve the engine noise?

[Vissa]

The only thing you gain is the PSSSST noice it makes. Nothing else for daily driving.

[seat-ibiza-jake]

Hi mate, I have the same engine as you. I also wanted the classic "pshhhhhhhh" sound when I lifted off the throttle. Then I read that this can actually decrease performance. Have a read of this below:

Firstly you have to ask yourself, "Why do you want an after market unit?" The Impreza is equiped with a satisfactory DV as standard.
The blow off valve does not increase performance. In fact the best performance increase can be gained by not having one altogether, the WRC cars do not run one.
BUT...
...the main advantage of the blow off valve is to reduce stress upon the turbo blades when you lift off of the accelerator to lets say change gear. The turbine is still spinning and thus pumping gas into the input...but the engine is off power. So what to do with the excess. A blow off valve set to a certain pressure releases this excess. A vent to atmosphere allows it to go to air giving the characteristic pfffft, a recirculating one feeds it back into the input of the turbo thus keeping the system pressurised. When you hit the accelerator the vented system then needs to momentarily build up the pressure again whilst the recirculating system doesn't.
Without a BOV the turbine can actually stall or air is drawn back through the wastegate in the wrong direction. The turbine is spinning but there are no exhaust gases coming out of the engine, so it either stalls or draws airthrough the wastegate from the exhaust side.This is the chirp you hear on the WRC cars. The stress on the bearings is quite substantial and in a completely different direction to that which the turbo is designed. The turbo in the WRC cars has a 360 degree bearing surface to counter this (and the turbo is changed and refurbished per rally if not sooner), the road going turbo does not.
After market BOVs are adjustable, and the pressure at which they blow can be set higher than standard which means that there is more pressure retained at gear change.... BUT how high can you go, what is a safe setting and will it ultimately shorten the life of the turbo?
The other reason an aftermarket BOV is selected is if the system is running more boost than stock and the stock BOV can not operate at the elevated levels.
Finally the main reason I can see a BOV is fitted is because people want that characteristic PFFFT! which probably loses them performance rather than gain it as they are dumping turbine pressure everytime they change gear. One other negative thing about vent to atmosphere BOVs is that the ECU monitors the air into the system via the MAF. This is in the input before the recirculating pipework reintroduces the gases back into the system. Thus the ECU takes into account this recirculated air in its calculation for fueling, and ultimately over fuels for a VTA-BOV and won't do the turbo much good or any following catalyst in the exhaust.

Personally i have fitted 5 different bov's to my impreza over the last 2 years: baileys,forge,gfb,turbosmart & a blitz,and in all honesty the car has run much sweeter with the std recirc on. If on the other hand you have your car mapped with one fitted ,then at least the mapper can compensate for the overfuelling.


I know the guy in the above text has an impreza but I bet the mechanics of how a turbo works don't change, any thoughts?

[Gti1927]

im not an expert on turbos but you wont ever have no exhaust gases running through the turbo as your always producing exhaust gas when the car is running! That's part of the combustion cycle! As for the dumping of air its self it doesn't dump all the air just the excess as again your always going to be drawing air for the combustion cycle.

[vc-10]

Quite a lot of modern turbos are variable geometry too, which helps maintain the turbo's rpm. Not sure if the 1.2 TSI's turbo is a variable geometry one, but it's worth bearing in mind.

[B1N9S]

It's worth bearing in mind too, you will be forking out £165 notes to get your little Polo to make a stupid noise every time you change gear !!!!

[vc-10]

There's a Mk.5 Golf GTI around me that's been really badly modded, with a blow-off valve. Poor thing sounds really ill- I think the money he should have spent on servicing has been spent on an ill-fitting bodykit and the valve...

[Wolfi]

Yeah, them valves and the noise they make have a reputation for being a bit chavvy
Imprezas, Corsas, Saxos etc.....

[vc-10]

It's when you hear that sort of noise coming from something you know full well doesn't have a turbo (with one of those 'fake turbo sound' things) that it gets me. Such as a 1.0 Corsa.

[PogoCT]

I wouldn't bother fitting those things.... in traffic you will be annoyed to no end, imagine the laughter when you in an enclosed parking lot and all you hear is pssssh psssssh pssssh and it's a little polo -

[Lucaio]

Is it wrong that I think the pssshhh noise is pretty "cool"? But then again I think those undercar neons/leds are pretty "cool".

Note: I know the above mentioned are pretty chavvy, but I can assure you I'm no chav. I just spent most of my teenage years playing Need for Speed Underground and watching Fast and Furious.