Blow off valves.....

Hi guys, i was reading the other day that blow off valves actually serve a purpose, as i thought they were just a wank thing. has anyone on the site fitted one, or can they be fitted to any turbo and in the ZD30 is it worth fitting one to. cos as far as i know they release the pressure in the induction side of the turbo, like when changing gears to stop the turbo unnaturally spooling down to quick due to the engine not needing the boost at that given time. is this right and do yous reckon its something worth doing down the track, Cheers

Matty

my missus is constantly compalining about my blow off valve lol

Nah seriously that is pretty much what they do, the help the turbo stay on boost between gear changes etc, as for their benefit on a diesel, I have no idea sorry.

Not really needed on a diesel, as it doesn't have a throtle body.

In a manual trans petrol engine when you change gears you close the throtle body, increasing the pressure in the intake, if its not released it can really slow the turbo down and creates lag.

Agree, useless on a diesel. From what I know, the difference between one that makes you a wanker and one that just makes your car a little faster is whether they vent pressure to the atmosphere with a trumpet (PFFSSSSCH!) or back into the air intake upstream of the turbo.

they do work on a diesel. the amount of effect is not a lot and really depends on how laggy the motor is and driving style.
personally i think money is better spent elsewhere. but if you have plenty of $$ and want the absolutely last bit of performance then its a good mod to do.

tweak'e said:

they do work on a diesel.

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How's that?

Pro-Nav2.7TDi said:

How's that?

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releases pressure in the intake during gearchanges. especially with the high boost motors when you slow down suddenly the boost tries to go backwoulds through the turbo. that slows the turbo down. releasing the pressure lets the turbo keep spinning so you get boost back up quicker after the gear change.

how they work without vac in the intake? use system vaccum and trigger it with micro switch and vac solinoid (typically idle switch and/or clutch switch)

tweak'e said:

use system vaccum and trigger it with micro switch and vac solinoid (typically idle switch and/or clutch switch)

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Oh. Thanks.

Not to be overly negative, but it seems like a bit of a complex waste of time on these low-output road car diesels?

I guess you already said that in your earlier post.

yep a lot of hassle and cost for stuff all.
apparantly if your running 30+ psi boost they actually help save the turbo from a lot of wear.

tweak'e said:

apparantly if your running 30+ psi boost they actually help save the turbo from a lot of wear.

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Really? That's actually kind of cool. I maintain though that releasing pressure into the atmosphere rather than environs with existing sound pollution controls (intake or exhaust) is just to make people think you buy XL underwear.

have a search on "turbo bark" with high boost even just the slowing of the engine is enough to cause the boost to push back through and stall the turbo. that can put a lot of strain on the bearings.

im pretty sure most diesel'have an internal waste gate so that the pressure goes through there, and that is how ya get the wwwhoooo sound when changing gears with a modified exhaust.
and with a petrol turbo there an external waste gate which is the need for a blow off valve.
that's my understanding of it

ok, so basically on the ZD30 there is no need for one to be fitted. the internal wastegate on these turbos does that vent into the exhaust when the pressure drops off. also, is it true that when the turbo has exceeded max boost the wastegate will open, by passing the turbo so it cant boost any higher.

A wastegate is a bypass valve that lets exhaust gas out without routing it through the exhaust turbine. This in effect adjusts how fast the turbo spins at any given moment. This is what controls how much boost is being generated.

Internal type is built into the turbo exhaust housing and an external type is just that. External to the turbo its self.

The sneezing sound associated with most ricers does not come from the wastegate. It comes from a blow off valve on the engines intake.

As has been said already it is of no real use on an engine with no throttle plate. (ie; diesel).

Kickars2 said:

im pretty sure most diesel'have an internal waste gate so that the pressure goes through there, and that is how ya get the wwwhoooo sound when changing gears with a modified exhaust.
and with a petrol turbo there an external waste gate which is the need for a blow off valve.
that's my understanding of it

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Kickers2, not the case.

Both petrol and diesels can have either.

Wastegates control the amount of exhaust gases with go through the turbine side of the turbo. They allow (some) exhaust gases to bypass the turbo when running at maximum boost. This is what limits the amount of boost.

Essentually they have a diaphram with a spring at one end and a chamber connected to the intake (post turbo) Once the air pressure exceeds the pressure of the spring the valve is opened, allowing the gasses to bypass the turbo.

Wastegates, both internal and external, do exactly the same job, but external helps create better flow characteristics (ie smooth instead of turbulent)

BOV's release the excess pressure when closing the throtle on a petrol car (between throtle body and turbo), this helps eliminate lag, stops the turbo from being shock loaded (ie being slowed to fast), etc

all right then, you learn something new everyday. so if any turbo car starts over boosting the the pressure spring in the wastegate would be one of the first things to check. one last thing, has anyone done or heard of upgrading the turbos on the ZD30. just though it would be interesting to see so. cheers

matty said:

all right then, you learn something new everyday. so if any turbo car starts over boosting the the pressure spring in the wastegate would be one of the first things to check.

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Matty, usually due to the air suply to the wastegate spring. This is where aftermarket boost controller attach to, adjusting the pressure to the spring.

matty said:

one last thing, has anyone done or heard of upgrading the turbos on the ZD30. just though it would be interesting to see so. cheers

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Easily done, just require matching flanges. A suitability sized ball bearing watercooled would be nice! Might eliminate some of the lag and give a stronger top end , but prob not worth the $$$